diff --git a/agent/context/context.go b/agent/context/context.go
index dd071a2c..eda88171 100644
--- a/agent/context/context.go
+++ b/agent/context/context.go
@@ -87,6 +87,17 @@ func (ctx *Context) Release() {
 	ctx = nil
 }
 
+// Send sends data to the context's writer
+// This is used by the output module to send messages to the client
+func (ctx *Context) Send(data []byte) error {
+	if ctx.Writer == nil {
+		return nil // No writer, silently ignore
+	}
+
+	_, err := ctx.Writer.Write(data)
+	return err
+}
+
 // Map the context to a map
 func (ctx *Context) Map() map[string]interface{} {
 	data := map[string]interface{}{}
diff --git a/agent/llm/handlers/stream.go b/agent/llm/handlers/stream.go
index 5e1be574..39189fb6 100644
--- a/agent/llm/handlers/stream.go
+++ b/agent/llm/handlers/stream.go
@@ -2,62 +2,215 @@ package handlers
 
 import (
 	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output"
+	"github.com/yaoapp/yao/agent/output/message"
 )
 
 // DefaultStreamHandler creates a default stream handler that sends messages via context
 // This handler is used when no custom handler is provided
 func DefaultStreamHandler(ctx *context.Context) context.StreamFunc {
+	// Create stream state manager
+	state := &streamState{
+		ctx:       ctx,
+		inGroup:   false,
+		currentID: "",
+	}
+
 	return func(chunkType context.StreamChunkType, data []byte) int {
-		// TODO: Implement default stream handling
-		// - Parse streaming chunk data based on chunkType
-		// - Extract content from chunk
-		// - Send message via ctx (SSE, WebSocket, etc.)
-		// - Handle different chunk types (text, thinking, tool_calls, etc.)
-		// - Return 0 to continue streaming, non-zero to stop
-
+		// Handle different chunk types
 		switch chunkType {
-		case context.ChunkText:
-			// Handle text content
-		case context.ChunkThinking:
-			// Handle reasoning/thinking content
-		case context.ChunkToolCall:
-			// Handle tool calls
-		case context.ChunkMetadata:
-			// Handle metadata (usage, finish_reason)
-		case context.ChunkError:
-			// Handle error
-			return 1 // Stop on error
-		}
+		case context.ChunkStreamStart:
+			return state.handleStreamStart(data)
 
-		return 0 // Continue streaming
+		case context.ChunkGroupStart:
+			return state.handleGroupStart(data)
+
+		case context.ChunkText:
+			return state.handleText(data)
+
+		case context.ChunkThinking:
+			return state.handleThinking(data)
+
+		case context.ChunkToolCall:
+			return state.handleToolCall(data)
+
+		case context.ChunkMetadata:
+			return state.handleMetadata(data)
+
+		case context.ChunkError:
+			return state.handleError(data)
+
+		case context.ChunkGroupEnd:
+			return state.handleGroupEnd(data)
+
+		case context.ChunkStreamEnd:
+			return state.handleStreamEnd(data)
+
+		default:
+			// Unknown chunk type, continue
+			return 0
+		}
 	}
 }
 
-// SendStreamChunk sends a stream chunk via context
-// Used internally by DefaultStreamHandler
-func SendStreamChunk(ctx *context.Context, chunkType context.StreamChunkType, data []byte) error {
-	// TODO: Implement sending stream chunk
-	// - Format chunk for transport (SSE, WebSocket)
-	// - Send via ctx's connection
-	// - Handle errors and retries
-	return nil
+// streamState manages the state of the streaming process
+type streamState struct {
+	ctx       *context.Context
+	inGroup   bool
+	currentID string
+	buffer    []byte
 }
 
-// FormatSSE formats streaming data as Server-Sent Events format
-func FormatSSE(chunkType context.StreamChunkType, data []byte) string {
-	// TODO: Implement SSE formatting
-	// - Format as "data: {...}\n\n"
-	// - Include chunk type in the message
-	// - Handle special cases (done, error)
-	// - Ensure proper JSON encoding
-	return ""
+// handleStreamStart handles stream start event
+func (s *streamState) handleStreamStart(data []byte) int {
+	// Send loading message to indicate stream has started
+	msg := output.NewLoadingMessage("Connecting...")
+	output.Send(s.ctx, msg)
+	return 0 // Continue
 }
 
-// FormatWebSocket formats streaming data as WebSocket message
-func FormatWebSocket(chunkType context.StreamChunkType, data []byte) []byte {
-	// TODO: Implement WebSocket formatting
-	// - Format as JSON message with chunk type
-	// - Add message type/metadata
-	// - Handle binary vs text frames
-	return nil
+// handleGroupStart handles group start event
+func (s *streamState) handleGroupStart(data []byte) int {
+	s.inGroup = true
+	s.currentID = generateMessageID()
+	s.buffer = []byte{}
+	return 0 // Continue
+}
+
+// handleText handles text content chunks
+func (s *streamState) handleText(data []byte) int {
+	if len(data) == 0 {
+		return 0
+	}
+
+	// Ensure we have a message ID
+	if s.currentID == "" {
+		s.currentID = generateMessageID()
+	}
+
+	// Append to buffer
+	s.buffer = append(s.buffer, data...)
+
+	// Send delta message
+	msg := &message.Message{
+		ID:    s.currentID,
+		Type:  message.TypeText,
+		Delta: true,
+		Props: map[string]interface{}{
+			"content": string(data),
+		},
+	}
+
+	if err := output.Send(s.ctx, msg); err != nil {
+		// Log error but continue streaming
+		return 0
+	}
+
+	return 0 // Continue
+}
+
+// handleThinking handles thinking/reasoning chunks
+func (s *streamState) handleThinking(data []byte) int {
+	if len(data) == 0 {
+		return 0
+	}
+
+	// Ensure we have a message ID
+	if s.currentID == "" {
+		s.currentID = generateMessageID()
+	}
+
+	// Append to buffer
+	s.buffer = append(s.buffer, data...)
+
+	// Send delta message
+	msg := &message.Message{
+		ID:    s.currentID,
+		Type:  message.TypeThinking,
+		Delta: true,
+		Props: map[string]interface{}{
+			"content": string(data),
+		},
+	}
+
+	if err := output.Send(s.ctx, msg); err != nil {
+		return 0
+	}
+
+	return 0 // Continue
+}
+
+// handleToolCall handles tool call chunks
+func (s *streamState) handleToolCall(data []byte) int {
+	// Tool calls are usually complete JSON objects
+	// Parse and send as tool_call message
+	msg := &message.Message{
+		ID:    generateMessageID(),
+		Type:  message.TypeToolCall,
+		Delta: true,
+		Props: map[string]interface{}{
+			// TODO: Parse tool call data
+			"raw": string(data),
+		},
+	}
+
+	output.Send(s.ctx, msg)
+	return 0 // Continue
+}
+
+// handleMetadata handles metadata chunks (usage, finish_reason, etc.)
+func (s *streamState) handleMetadata(data []byte) int {
+	// Metadata is usually not displayed to users
+	// Could be logged or stored for analytics
+	return 0 // Continue
+}
+
+// handleError handles error chunks
+func (s *streamState) handleError(data []byte) int {
+	// Send error message
+	msg := output.NewErrorMessage(string(data), "stream_error")
+	output.Send(s.ctx, msg)
+
+	return 1 // Stop streaming on error
+}
+
+// handleGroupEnd handles group end event
+func (s *streamState) handleGroupEnd(data []byte) int {
+	if !s.inGroup {
+		return 0
+	}
+
+	// Send done message with complete content
+	if s.currentID != "" && len(s.buffer) > 0 {
+		msg := &message.Message{
+			ID:   s.currentID,
+			Type: message.TypeText, // Default to text
+			Done: true,
+			Props: map[string]interface{}{
+				"content": string(s.buffer),
+			},
+		}
+		output.Send(s.ctx, msg)
+	}
+
+	// Reset state
+	s.inGroup = false
+	s.currentID = ""
+	s.buffer = []byte{}
+
+	return 0 // Continue
+}
+
+// handleStreamEnd handles stream end event
+func (s *streamState) handleStreamEnd(data []byte) int {
+	// Flush any remaining data
+	output.Flush(s.ctx)
+	return 0 // Continue (stream will end naturally)
+}
+
+// generateMessageID generates a unique message ID
+func generateMessageID() string {
+	// TODO: Implement proper ID generation
+	// For now, use a simple approach
+	return output.GenerateID()
 }
diff --git a/agent/output/BUILTIN_TYPES.md b/agent/output/BUILTIN_TYPES.md
new file mode 100644
index 00000000..c0d04ce1
--- /dev/null
+++ b/agent/output/BUILTIN_TYPES.md
@@ -0,0 +1,526 @@
+# Built-in Message Types
+
+Built-in message types are standardized types that all adapters must support. These types have predefined Props structures to ensure consistency across different output formats.
+
+## Type Constants
+
+Defined in `types.go`:
+
+```go
+const (
+    TypeText     = "text"      // Plain text or Markdown content
+    TypeThinking = "thinking"  // Reasoning/thinking process
+    TypeLoading  = "loading"   // Loading/processing indicator
+    TypeToolCall = "tool_call" // LLM tool/function call
+    TypeError    = "error"     // Error message
+    TypeImage    = "image"     // Image content
+    TypeAudio    = "audio"     // Audio content
+    TypeVideo    = "video"     // Video content
+    TypeAction   = "action"    // System action (silent in standard clients)
+)
+```
+
+## Standard Props Structures
+
+### 1. Text (`text`)
+
+**Purpose:** Plain text or Markdown content
+
+**Props Structure:**
+
+```go
+type TextProps struct {
+    Content string `json:"content"` // Text content (supports Markdown)
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "text",
+  "props": {
+    "content": "Hello **world**!"
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewTextMessage("Hello **world**!")
+```
+
+---
+
+### 2. Thinking (`thinking`)
+
+**Purpose:** Reasoning or thinking process (used by o1 models, DeepSeek R1, etc.)
+
+**Props Structure:**
+
+```go
+type ThinkingProps struct {
+    Content string `json:"content"` // Reasoning/thinking content
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "thinking",
+  "props": {
+    "content": "Let me analyze this step by step..."
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewThinkingMessage("Let me analyze this step by step...")
+```
+
+---
+
+### 3. Loading (`loading`)
+
+**Purpose:** Loading or processing indicator (preprocessing, knowledge base search, data fetching, etc.)
+
+**Props Structure:**
+
+```go
+type LoadingProps struct {
+    Message string `json:"message"` // Loading message
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "loading",
+  "props": {
+    "message": "Searching knowledge base..."
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewLoadingMessage("Searching knowledge base...")
+```
+
+**Use Cases:**
+
+- Knowledge base search: `"Searching knowledge base..."`
+- Data preprocessing: `"Processing uploaded file..."`
+- External API calls: `"Fetching data from API..."`
+- Database queries: `"Querying database..."`
+
+**Example in Hook:**
+
+```go
+// In Create hook, show preprocessing steps
+func Create(ctx *context.Context, messages []context.Message) (*context.HookCreateResponse, error) {
+    // Send loading message for knowledge base search
+    output.Send(ctx, output.NewLoadingMessage("Searching knowledge base..."))
+
+    // Do the actual search
+    results := searchKnowledgeBase(messages)
+
+    // Send another loading message for processing
+    output.Send(ctx, output.NewLoadingMessage("Processing results..."))
+
+    // Process and return
+    return &context.HookCreateResponse{
+        Messages: buildMessages(results),
+    }, nil
+}
+```
+
+**Result in OpenAI Client:**
+
+- Shows as thinking/reasoning process
+- User sees "Searching knowledge base..." and "Processing results..."
+- Provides transparency into what's happening
+
+---
+
+### 4. Tool Call (`tool_call`)
+
+**Purpose:** LLM tool or function call
+
+**Props Structure:**
+
+```go
+type ToolCallProps struct {
+    ID        string `json:"id"`                  // Tool call ID
+    Name      string `json:"name"`                // Function/tool name
+    Arguments string `json:"arguments,omitempty"` // JSON string of arguments
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "tool_call",
+  "props": {
+    "id": "call_abc123",
+    "name": "get_weather",
+    "arguments": "{\"location\": \"San Francisco\"}"
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewToolCallMessage(
+    "call_abc123",
+    "get_weather",
+    "{\"location\": \"San Francisco\"}",
+)
+```
+
+---
+
+### 5. Error (`error`)
+
+**Purpose:** Error message
+
+**Props Structure:**
+
+```go
+type ErrorProps struct {
+    Message string `json:"message"`           // Error message
+    Code    string `json:"code,omitempty"`    // Error code
+    Details string `json:"details,omitempty"` // Additional error details
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "error",
+  "props": {
+    "message": "Connection timeout",
+    "code": "TIMEOUT",
+    "details": "Failed to connect to database after 30s"
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewErrorMessage("Connection timeout", "TIMEOUT")
+```
+
+---
+
+### 6. Action (`action`)
+
+**Purpose:** System-level action/command (not displayed to user, only processed by client)
+
+**Props Structure:**
+
+```go
+type ActionProps struct {
+    Name    string                 `json:"name"`              // Action name
+    Payload map[string]interface{} `json:"payload,omitempty"` // Action parameters
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "action",
+  "props": {
+    "name": "open_panel",
+    "payload": {
+      "panel_id": "user_profile",
+      "user_id": "123"
+    }
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewActionMessage("open_panel", map[string]interface{}{
+    "panel_id": "user_profile",
+    "user_id": "123",
+})
+```
+
+**Use Cases:**
+
+- Open sidebar/panel: `"open_panel"`
+- Navigate to page: `"navigate"`
+- Trigger UI update: `"refresh_view"`
+- Close modal: `"close_modal"`
+- Scroll to element: `"scroll_to"`
+
+**Important Notes:**
+
+- **Silent in OpenAI clients**: Action messages are NOT sent to standard chat clients
+- **CUI clients only**: Only CUI clients process action messages
+- **System-level**: Used for controlling the UI/application, not chat content
+
+**Example in Hook:**
+
+```go
+// Send action to open a panel with user details
+output.Send(ctx, output.NewActionMessage("open_panel", map[string]interface{}{
+    "panel_id": "user_details",
+    "user_id":  user.ID,
+}))
+
+// Send text message (visible to user)
+output.Send(ctx, output.NewTextMessage("I've opened the user details panel for you."))
+```
+
+**Result:**
+
+- **CUI client**: Panel opens, text message displays
+- **OpenAI client**: Only text message displays (action is silent)
+
+---
+
+### 7. Image (`image`)
+
+**Purpose:** Image content
+
+**Props Structure:**
+
+```go
+type ImageProps struct {
+    URL    string  // Required: Image URL or base64 data
+    Alt    string  // Alternative text
+    Width  int     // Image width in pixels
+    Height int     // Image height in pixels
+    Detail string  // OpenAI detail level: "auto", "low", "high"
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "image",
+  "props": {
+    "url": "https://example.com/avatar.jpg",
+    "alt": "User avatar",
+    "width": 200,
+    "height": 200
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewImageMessage("https://example.com/avatar.jpg", "User avatar")
+```
+
+**Adapter Behavior:**
+
+- **CUI**: Renders image directly with `<img>` tag
+- **OpenAI**: Converts to Markdown `![alt](url)` - **displays inline** in Markdown-supporting clients
+
+---
+
+### 8. Audio (`audio`)
+
+**Purpose:** Audio content
+
+**Props Structure:**
+
+```go
+type AudioProps struct {
+    URL        string   // Required: Audio URL or base64 data
+    Format     string   // Audio format: "mp3", "wav", "ogg"
+    Duration   float64  // Duration in seconds
+    Transcript string   // Audio transcript text
+    Autoplay   bool     // Whether to autoplay
+    Controls   bool     // Whether to show controls
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "audio",
+  "props": {
+    "url": "https://example.com/audio.mp3",
+    "format": "mp3",
+    "duration": 120.5,
+    "transcript": "This is the audio content...",
+    "controls": true
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewAudioMessage("https://example.com/audio.mp3", "mp3")
+```
+
+**Adapter Behavior:**
+
+- **CUI**: Renders audio player with controls
+- **OpenAI**: Converts to link `🔊 [Play Audio](url)` - can't display inline
+
+---
+
+### 9. Video (`video`)
+
+**Purpose:** Video content
+
+**Props Structure:**
+
+```go
+type VideoProps struct {
+    URL       string   // Required: Video URL
+    Format    string   // Video format: "mp4", "webm"
+    Duration  float64  // Duration in seconds
+    Thumbnail string   // Thumbnail/poster image URL
+    Width     int      // Video width in pixels
+    Height    int      // Video height in pixels
+    Autoplay  bool     // Whether to autoplay
+    Controls  bool     // Whether to show controls
+    Loop      bool     // Whether to loop
+}
+```
+
+**Example:**
+
+```json
+{
+  "type": "video",
+  "props": {
+    "url": "https://example.com/video.mp4",
+    "format": "mp4",
+    "thumbnail": "https://example.com/poster.jpg",
+    "width": 640,
+    "height": 360,
+    "controls": true
+  }
+}
+```
+
+**Helper:**
+
+```go
+msg := output.NewVideoMessage("https://example.com/video.mp4")
+```
+
+**Adapter Behavior:**
+
+- **CUI**: Renders video player with controls
+- **OpenAI**: Converts to link `🎬 [Watch Video](url)` - can't display inline
+
+---
+
+## Adapter Requirements
+
+All adapters (CUI, OpenAI, etc.) **must** support these built-in types with their standard Props structures.
+
+### CUI Adapter
+
+CUI adapter passes built-in types through without transformation:
+
+```json
+{
+  "type": "text",
+  "props": {
+    "content": "Hello world"
+  }
+}
+```
+
+### OpenAI Adapter
+
+OpenAI adapter converts built-in types to OpenAI format:
+
+| Type        | OpenAI Format             | Field                         | Note                                      |
+| ----------- | ------------------------- | ----------------------------- | ----------------------------------------- |
+| `text`      | `delta.content`           | `props.content`               |                                           |
+| `thinking`  | `delta.reasoning_content` | `props.content`               | Reasoning content (o1 models)             |
+| `loading`   | `delta.reasoning_content` | `props.message`               | Shows as thinking in OpenAI clients       |
+| `tool_call` | `delta.tool_calls`        | `props.{id, name, arguments}` |                                           |
+| `error`     | `error`                   | `props.{message, code}`       |                                           |
+| `image`     | `delta.content`           | `props.{url, alt}`            | Markdown: `![alt](url)` - displays inline |
+| `audio`     | `delta.content`           | `props.url`                   | Markdown link (can't display inline)      |
+| `video`     | `delta.content`           | `props.url`                   | Markdown link (can't display inline)      |
+| `action`    | (not sent)                | -                             | Silent - system actions only              |
+
+---
+
+## Custom Types
+
+Any type **not** in the built-in list is considered a custom type. Adapters may handle custom types differently:
+
+- **CUI:** Pass through as-is
+- **OpenAI:** Convert to Markdown link
+
+Example custom type:
+
+```json
+{
+  "type": "image",
+  "props": {
+    "url": "https://example.com/image.jpg",
+    "alt": "Description"
+  }
+}
+```
+
+---
+
+## Checking Built-in Types
+
+```go
+// Check if a type is built-in
+if output.IsBuiltinType(msg.Type) {
+    // Handle as standard type
+} else {
+    // Handle as custom type
+}
+```
+
+---
+
+## Guidelines for New Built-in Types
+
+When adding new built-in types:
+
+1. ✅ Add constant to `types.go`
+2. ✅ Define Props structure
+3. ✅ Add helper function in `builtin.go`
+4. ✅ Update all adapters to support it
+5. ✅ Document in this file
+6. ✅ Add tests
+
+**Only add built-in types for:**
+
+- Universal concepts (text, errors, etc.)
+- LLM-specific features (thinking, tool_calls)
+- Types that need cross-adapter consistency
+
+**Do NOT add built-in types for:**
+
+- UI components (buttons, forms, etc.)
+- Rich media (images, videos, etc.)
+- Application-specific widgets
+
+These should remain custom types.
diff --git a/agent/output/README.md b/agent/output/README.md
new file mode 100644
index 00000000..95c976d0
--- /dev/null
+++ b/agent/output/README.md
@@ -0,0 +1,445 @@
+# Output Module
+
+The output module provides a unified API for sending messages to different client types (CUI, OpenAI-compatible, etc.) with support for streaming and rich media content.
+
+## Architecture
+
+```
+agent/output/
+├── message/              # Core types and interfaces (no dependencies)
+│   ├── types.go         # Message, MessageGroup, Props structures
+│   └── interfaces.go    # Writer, Adapter, Factory interfaces
+├── adapters/            # Client-specific adapters
+│   ├── cui/             # CUI adapter (native DSL)
+│   │   ├── adapter.go
+│   │   └── writer.go
+│   └── openai/          # OpenAI adapter (converts to OpenAI format)
+│       ├── adapter.go
+│       ├── converter.go
+│       ├── writer.go
+│       ├── types.go
+│       └── factory.go
+├── output.go            # Main API (Send, GetWriter, etc.)
+├── builtin.go           # Helper functions for built-in types
+└── BUILTIN_TYPES.md     # Documentation for built-in types
+```
+
+## DSL Structure
+
+### Message Structure
+
+The universal message DSL is a JSON structure that supports streaming, rich media, and incremental updates:
+
+```go
+type Message struct {
+    // Core fields
+    Type  string                 `json:"type"`            // Message type (e.g., "text", "image", "action")
+    Props map[string]interface{} `json:"props,omitempty"` // Type-specific properties
+
+    // Streaming control
+    ID    string `json:"id,omitempty"`    // Unique message ID (for merging in streaming)
+    Delta bool   `json:"delta,omitempty"` // Whether this is an incremental update
+    Done  bool   `json:"done,omitempty"`  // Whether the message is complete
+
+    // Delta update control (for incremental props updates)
+    DeltaPath   string `json:"delta_path,omitempty"`   // Which field to update (e.g., "content", "items.0.name")
+    DeltaAction string `json:"delta_action,omitempty"` // How to update ("append", "replace", "merge", "set")
+
+    // Type correction (for streaming type inference)
+    TypeChange bool `json:"type_change,omitempty"` // Marks this as a type correction message
+
+    // Message grouping (for semantically related messages)
+    GroupID    string `json:"group_id,omitempty"`    // Parent message group ID
+    GroupStart bool   `json:"group_start,omitempty"` // Marks the start of a group
+    GroupEnd   bool   `json:"group_end,omitempty"`   // Marks the end of a group
+
+    // Metadata
+    Metadata *Metadata `json:"metadata,omitempty"` // Timestamp, sequence, trace ID
+}
+```
+
+### Field Descriptions
+
+#### Core Fields
+
+- **`Type`** (required): Determines how the message should be rendered
+
+  - Built-in types: `text`, `thinking`, `loading`, `tool_call`, `error`, `image`, `audio`, `video`, `action`
+  - Custom types: Any string (frontend must have corresponding component)
+
+- **`Props`** (optional): Type-specific properties passed to the rendering component
+  - For `text`: `{"content": "Hello"}`
+  - For `image`: `{"url": "...", "alt": "..."}`
+  - For custom types: Any JSON-serializable data
+
+#### Streaming Control
+
+- **`ID`** (optional): Unique identifier for message tracking
+
+  - Used to merge multiple delta updates into a single message
+  - Auto-generated if not provided
+  - Example: `"msg_1234567890_9876543210"`
+
+- **`Delta`** (optional): Marks this as an incremental update
+
+  - `true`: Append/update to existing message with same ID
+  - `false`: Complete message (default)
+  - Used for streaming LLM responses
+
+- **`Done`** (optional): Marks message as complete
+  - `true`: No more updates will come for this message ID
+  - `false`: More updates may follow
+  - Typically sent as final message in a delta sequence
+
+#### Delta Update Control
+
+For complex, structured messages that need field-level updates:
+
+- **`DeltaPath`** (optional): JSON path to the field being updated
+
+  - Simple: `"content"` (updates `props.content`)
+  - Nested: `"user.name"` (updates `props.user.name`)
+  - Array: `"items.0.title"` (updates `props.items[0].title`)
+
+- **`DeltaAction`** (optional): How to apply the delta update
+  - `"append"`: Concatenate to existing string/array
+  - `"replace"`: Replace entire value
+  - `"merge"`: Merge objects (shallow merge)
+  - `"set"`: Set new field (if doesn't exist)
+
+#### Type Correction
+
+- **`TypeChange`** (optional): Indicates message type was corrected
+  - Used when initial type inference was wrong
+  - Frontend should re-render with new type
+  - Example: Initially sent as `text`, corrected to `thinking`
+
+#### Message Grouping
+
+For grouping semantically related messages (e.g., image + caption):
+
+- **`GroupID`** (optional): Identifier for the message group
+- **`GroupStart`** (optional): Marks the beginning of a group
+- **`GroupEnd`** (optional): Marks the end of a group
+
+#### Metadata
+
+- **`Metadata`** (optional): Additional message metadata
+  ```go
+  type Metadata struct {
+      Timestamp int64  // Unix nanoseconds
+      Sequence  int    // Message sequence number
+      TraceID   string // For debugging/logging
+  }
+  ```
+
+### Message Examples
+
+#### Simple Text Message
+
+```json
+{
+  "type": "text",
+  "props": {
+    "content": "Hello, world!"
+  }
+}
+```
+
+#### Streaming Text (Delta Updates)
+
+```json
+// First chunk
+{
+  "id": "msg_123",
+  "type": "text",
+  "delta": true,
+  "props": {
+    "content": "Hello"
+  }
+}
+
+// Second chunk (appends)
+{
+  "id": "msg_123",
+  "type": "text",
+  "delta": true,
+  "props": {
+    "content": ", world"
+  }
+}
+
+// Final chunk (marks done)
+{
+  "id": "msg_123",
+  "type": "text",
+  "delta": true,
+  "done": true,
+  "props": {
+    "content": "!"
+  }
+}
+```
+
+#### Complex Type with Nested Updates
+
+```json
+// Initial message
+{
+  "id": "msg_456",
+  "type": "table",
+  "props": {
+    "columns": ["Name", "Age"],
+    "rows": []
+  }
+}
+
+// Add first row
+{
+  "id": "msg_456",
+  "type": "table",
+  "delta": true,
+  "delta_path": "rows",
+  "delta_action": "append",
+  "props": {
+    "rows": [{"name": "Alice", "age": 30}]
+  }
+}
+
+// Add second row
+{
+  "id": "msg_456",
+  "type": "table",
+  "delta": true,
+  "delta_path": "rows",
+  "delta_action": "append",
+  "props": {
+    "rows": [{"name": "Bob", "age": 25}]
+  }
+}
+```
+
+#### Type Correction
+
+```json
+// Initial guess (text)
+{
+  "id": "msg_789",
+  "type": "text",
+  "delta": true,
+  "props": {
+    "content": "Let me think..."
+  }
+}
+
+// Correction (actually thinking)
+{
+  "id": "msg_789",
+  "type": "thinking",
+  "type_change": true,
+  "props": {
+    "content": "Let me think..."
+  }
+}
+```
+
+#### Message Group
+
+```json
+// Group start
+{
+  "group_id": "grp_001",
+  "group_start": true
+}
+
+// Image in group
+{
+  "type": "image",
+  "group_id": "grp_001",
+  "props": {
+    "url": "https://example.com/photo.jpg",
+    "alt": "Beautiful sunset"
+  }
+}
+
+// Caption in group
+{
+  "type": "text",
+  "group_id": "grp_001",
+  "props": {
+    "content": "Captured at Golden Gate Bridge"
+  }
+}
+
+// Group end
+{
+  "group_id": "grp_001",
+  "group_end": true
+}
+```
+
+## Key Design Decisions
+
+### 1. Separate `message` Package
+
+To avoid circular dependencies, all core types and interfaces are defined in the `message` sub-package:
+
+- `message.Message` - Universal message DSL
+- `message.Writer` - Interface for writing messages
+- `message.Adapter` - Interface for format conversion
+
+This allows:
+
+- `handlers` → `output` → `message` ✅
+- `output/adapters` → `message` ✅
+- No circular dependencies!
+
+### 2. Adapter Pattern
+
+Different clients require different formats:
+
+**CUI Clients:**
+
+```json
+{
+  "type": "text",
+  "props": { "content": "Hello" }
+}
+```
+
+**OpenAI Clients:**
+
+```json
+{
+  "choices": [
+    {
+      "delta": { "content": "Hello" }
+    }
+  ]
+}
+```
+
+Adapters handle the transformation automatically based on `ctx.Accept`.
+
+### 3. Built-in Types
+
+9 standardized message types with defined Props structures:
+
+| Type        | Purpose            | CUI     | OpenAI                    |
+| ----------- | ------------------ | ------- | ------------------------- |
+| `text`      | Text content       | Direct  | `delta.content`           |
+| `thinking`  | LLM reasoning      | Direct  | `delta.reasoning_content` |
+| `loading`   | Progress indicator | Direct  | `delta.reasoning_content` |
+| `tool_call` | Function calls     | Direct  | `delta.tool_calls`        |
+| `error`     | Error messages     | Direct  | `error`                   |
+| `image`     | Images             | Render  | `![](url)` markdown       |
+| `audio`     | Audio              | Player  | Link                      |
+| `video`     | Video              | Player  | Link                      |
+| `action`    | System commands    | Execute | Silent                    |
+
+## Usage
+
+### Basic Usage
+
+```go
+import (
+    "github.com/yaoapp/yao/agent/output"
+    "github.com/yaoapp/yao/agent/output/message"
+)
+
+// Send a text message
+msg := output.NewTextMessage("Hello world")
+output.Send(ctx, msg)
+
+// Send a loading indicator
+loading := output.NewLoadingMessage("Searching knowledge base...")
+output.Send(ctx, loading)
+
+// Send an image
+img := output.NewImageMessage("https://example.com/image.jpg", "Description")
+output.Send(ctx, img)
+
+// Send an error
+err := output.NewErrorMessage("Connection failed", "TIMEOUT")
+output.Send(ctx, err)
+```
+
+### Streaming Messages
+
+```go
+// Send delta (incremental) updates
+msg := &message.Message{
+    ID:    "msg_123",
+    Type:  message.TypeText,
+    Delta: true,  // Incremental update
+    Props: map[string]interface{}{
+        "content": "Hello",
+    },
+}
+output.Send(ctx, msg)
+
+// Mark as complete
+msg.Delta = false
+msg.Done = true
+msg.Props["content"] = "Hello world!"  // Full content
+output.Send(ctx, msg)
+```
+
+### Custom Writers
+
+```go
+// Register a custom writer factory
+factory := &MyCustomFactory{}
+output.SetWriterFactory(factory)
+
+// Now all calls to output.Send will use your custom writer
+```
+
+## Integration with Handlers
+
+The `handlers` package uses the output module for streaming:
+
+```go
+func DefaultStreamHandler(ctx *context.Context) context.StreamFunc {
+    return func(chunkType context.StreamChunkType, data []byte) int {
+        switch chunkType {
+        case context.ChunkText:
+            msg := output.NewTextMessage(string(data))
+            output.Send(ctx, msg)
+        case context.ChunkThinking:
+            msg := output.NewThinkingMessage(string(data))
+            output.Send(ctx, msg)
+        // ... handle other types
+        }
+        return 0 // Continue
+    }
+}
+```
+
+## Context-based Routing
+
+The output module automatically selects the right writer based on `ctx.Accept`:
+
+| `ctx.Accept`  | Writer | Format                |
+| ------------- | ------ | --------------------- |
+| `standard`    | OpenAI | OpenAI-compatible SSE |
+| `cui-web`     | CUI    | Universal DSL JSON    |
+| `cui-native`  | CUI    | Universal DSL JSON    |
+| `cui-desktop` | CUI    | Universal DSL JSON    |
+
+## Writer Caching
+
+Writers are cached per context to avoid recreating them:
+
+```go
+// Get or create writer (cached)
+writer := output.GetWriter(ctx)
+
+// Clear cache when done
+output.Close(ctx)  // Also closes the writer
+```
+
+## See Also
+
+- [BUILTIN_TYPES.md](./BUILTIN_TYPES.md) - Complete documentation of built-in message types
+- [adapters/openai/README.md](./adapters/openai/README.md) - OpenAI adapter documentation
diff --git a/agent/output/adapters/cui/adapter.go b/agent/output/adapters/cui/adapter.go
new file mode 100644
index 00000000..fbcb16b5
--- /dev/null
+++ b/agent/output/adapters/cui/adapter.go
@@ -0,0 +1,26 @@
+package cui
+
+import "github.com/yaoapp/yao/agent/output/message"
+
+// Adapter implements the message.Adapter interface for CUI clients.
+// It performs no conversion and outputs messages as-is, as CUI clients
+// are designed to directly consume the universal DSL.
+type Adapter struct{}
+
+// NewAdapter creates a new CUI adapter.
+func NewAdapter() *Adapter {
+	return &Adapter{}
+}
+
+// Adapt converts a universal Message to one or more client-specific chunks.
+// For CUI, it simply returns the original message as a single chunk.
+func (a *Adapter) Adapt(msg *message.Message) ([]interface{}, error) {
+	// CUI clients consume the universal DSL directly, so no conversion is needed.
+	return []interface{}{msg}, nil
+}
+
+// SupportsType checks if the adapter explicitly supports a given message type.
+// CUI adapter supports all types as it renders them directly.
+func (a *Adapter) SupportsType(msgType string) bool {
+	return true
+}
diff --git a/agent/output/adapters/cui/factory.go b/agent/output/adapters/cui/factory.go
new file mode 100644
index 00000000..1bac40fc
--- /dev/null
+++ b/agent/output/adapters/cui/factory.go
@@ -0,0 +1,25 @@
+package cui
+
+import (
+	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// Factory is the factory for creating CUI writers and adapters
+type Factory struct{}
+
+// NewFactory creates a new CUI factory
+func NewFactory() *Factory {
+	return &Factory{}
+}
+
+// CreateWriter creates a CUI writer
+func (f *Factory) CreateWriter(ctx *context.Context) (message.Writer, error) {
+	return NewWriter(ctx)
+}
+
+// CreateAdapter creates a CUI adapter
+func (f *Factory) CreateAdapter(ctx *context.Context) (message.Adapter, error) {
+	return NewAdapter(), nil
+}
+
diff --git a/agent/output/adapters/cui/writer.go b/agent/output/adapters/cui/writer.go
new file mode 100644
index 00000000..b14fb742
--- /dev/null
+++ b/agent/output/adapters/cui/writer.go
@@ -0,0 +1,79 @@
+package cui
+
+import (
+	"encoding/json"
+
+	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// Writer implements the message.Writer interface for CUI clients
+type Writer struct {
+	ctx     *context.Context
+	adapter *Adapter
+}
+
+// NewWriter creates a new CUI writer
+func NewWriter(ctx *context.Context) (*Writer, error) {
+	return &Writer{
+		ctx:     ctx,
+		adapter: NewAdapter(),
+	}, nil
+}
+
+// Write writes a single message to the output stream
+func (w *Writer) Write(msg *message.Message) error {
+	// CUI adapter passes messages through as-is
+	chunks, err := w.adapter.Adapt(msg)
+	if err != nil {
+		return err
+	}
+
+	// Send each chunk
+	for _, chunk := range chunks {
+		if err := w.sendChunk(chunk); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// WriteGroup writes a message group to the output stream
+func (w *Writer) WriteGroup(group *message.MessageGroup) error {
+	// For CUI, we send a group start message, all messages, then a group end message
+	// The group structure itself is also sent for clients that want it
+
+	// Send the group
+	if err := w.sendChunk(group); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Flush flushes any buffered data to the output stream
+func (w *Writer) Flush() error {
+	// For SSE, we don't need explicit flushing
+	// The underlying connection handles it
+	return nil
+}
+
+// Close closes the writer and cleans up resources
+func (w *Writer) Close() error {
+	// Nothing to clean up for CUI writer
+	return nil
+}
+
+// sendChunk sends a chunk to the output stream
+func (w *Writer) sendChunk(chunk interface{}) error {
+	// Convert chunk to JSON
+	data, err := json.Marshal(chunk)
+	if err != nil {
+		return err
+	}
+
+	// Send via context's writer
+	// The context knows how to send data based on the connection type (SSE, WebSocket, etc.)
+	return w.ctx.Send(data)
+}
diff --git a/agent/output/adapters/openai/README.md b/agent/output/adapters/openai/README.md
new file mode 100644
index 00000000..c90b0bfa
--- /dev/null
+++ b/agent/output/adapters/openai/README.md
@@ -0,0 +1,240 @@
+# OpenAI Adapter
+
+OpenAI adapter converts universal DSL messages to OpenAI-compatible format.
+
+## Conversion Rules
+
+### Built-in Types (Standard)
+
+These types are defined in `output.types.go` and have standardized Props structures that all adapters must support:
+
+| Message Type | Constant              | Props Structure | OpenAI Format             | Description                           |
+| ------------ | --------------------- | --------------- | ------------------------- | ------------------------------------- |
+| `text`       | `output.TypeText`     | `TextProps`     | `delta.content`           | Plain text or Markdown                |
+| `thinking`   | `output.TypeThinking` | `ThinkingProps` | `delta.reasoning_content` | Reasoning process (o1 models)         |
+| `loading`    | `output.TypeLoading`  | `LoadingProps`  | `delta.reasoning_content` | Loading indicator (shows as thinking) |
+| `tool_call`  | `output.TypeToolCall` | `ToolCallProps` | `delta.tool_calls`        | Tool/function calls                   |
+| `error`      | `output.TypeError`    | `ErrorProps`    | `error`                   | Error messages                        |
+| `action`     | `output.TypeAction`   | `ActionProps`   | (not sent)                | System actions (silent)               |
+
+### Custom Types
+
+All other message types (not in the built-in list) are converted to Markdown links:
+
+| Format                 | Example                         |
+| ---------------------- | ------------------------------- |
+| `delta.content` (link) | `"🖼️ [View Image](https://...)` |
+
+## Usage
+
+### Basic Usage
+
+```go
+import (
+    "github.com/yaoapp/yao/agent/output/adapters/openai"
+)
+
+// Create adapter with default config
+adapter := openai.NewAdapter()
+
+// Convert message
+chunks, err := adapter.Adapt(msg)
+```
+
+### With Custom Configuration
+
+```go
+// Create adapter with options
+adapter := openai.NewAdapter(
+    openai.WithBaseURL("https://api.example.com"),
+    openai.WithModel("gpt-4"),
+    openai.WithLinkTemplate("image", "🖼️ [View Image](%s)"),
+    openai.WithLinkTransformer(myOTPTransformer),
+)
+```
+
+### With Link Transformer (OTP)
+
+```go
+// Define OTP transformer
+func otpTransformer(url string, msgType string, msgID string) (string, error) {
+    // Generate OTP token
+    otp := generateOTP(msgID, 3600) // 1 hour expiry
+
+    // Create short link with OTP
+    shortURL := fmt.Sprintf("https://api.example.com/s/%s?t=%s", msgID, otp)
+
+    return shortURL, nil
+}
+
+// Use transformer
+adapter := openai.NewAdapter(
+    openai.WithLinkTransformer(otpTransformer),
+)
+```
+
+### Custom Converter
+
+```go
+// Register custom converter for a specific type
+adapter := openai.NewAdapter(
+    openai.WithConverter("my_widget", func(msg *output.Message, config *openai.AdapterConfig) ([]interface{}, error) {
+        // Custom conversion logic
+        return []interface{}{
+            // OpenAI format chunk
+        }, nil
+    }),
+)
+```
+
+## Examples
+
+### Text Message (Built-in Type)
+
+**Input (DSL):**
+
+```json
+{
+  "type": "text",
+  "props": {
+    "content": "Hello world"
+  }
+}
+```
+
+Or using helper:
+
+```go
+msg := output.NewTextMessage("Hello world")
+```
+
+**Output (OpenAI):**
+
+```json
+{
+  "id": "M1",
+  "object": "chat.completion.chunk",
+  "model": "yao-agent",
+  "choices": [
+    {
+      "delta": {
+        "content": "Hello world"
+      }
+    }
+  ]
+}
+```
+
+### Image Message
+
+**Input (DSL):**
+
+```json
+{
+  "id": "M2",
+  "type": "image",
+  "props": {
+    "url": "https://example.com/avatar.jpg"
+  }
+}
+```
+
+**Output (OpenAI):**
+
+```json
+{
+  "id": "M2",
+  "object": "chat.completion.chunk",
+  "model": "yao-agent",
+  "choices": [
+    {
+      "delta": {
+        "content": "🖼️ [View Image](https://api.example.com/s/M2?t=abc123)"
+      }
+    }
+  ]
+}
+```
+
+### Button Message
+
+**Input (DSL):**
+
+```json
+{
+  "id": "M3",
+  "type": "button",
+  "props": {
+    "text": "Approve",
+    "action": "workflow.approve"
+  }
+}
+```
+
+**Output (OpenAI):**
+
+```json
+{
+  "id": "M3",
+  "object": "chat.completion.chunk",
+  "model": "yao-agent",
+  "choices": [
+    {
+      "delta": {
+        "content": "🔘 [Approve](https://api.example.com/s/M3?t=abc123)"
+      }
+    }
+  ]
+}
+```
+
+## Link Templates
+
+Default templates:
+
+```go
+"image":  "🖼️ [View Image](%s)"
+"audio":  "🔊 [Play Audio](%s)"
+"video":  "🎬 [Watch Video](%s)"
+"file":   "📎 [Download File](%s)"
+"page":   "📄 [Open Page](%s)"
+"table":  "📊 [View Table](%s)"
+"chart":  "📈 [View Chart](%s)"
+"list":   "📋 [View List](%s)"
+"form":   "📝 [Fill Form](%s)"
+"button": "🔘 [%s](%s)" // Special: button text + link
+```
+
+Customize templates:
+
+```go
+adapter := openai.NewAdapter(
+    openai.WithLinkTemplate("image", "📷 Image: %s"),
+    openai.WithLinkTemplate("video", "🎥 Watch: %s"),
+)
+```
+
+## Link Transformer (TODO)
+
+The link transformer is currently left empty for future implementation of OTP/short link functionality.
+
+**Planned features:**
+
+- Generate one-time password (OTP) for secure access
+- Create short URLs for better readability
+- Set expiration time for links
+- Track link access for analytics
+
+**Example implementation:**
+
+```go
+func otpTransformer(url string, msgType string, msgID string) (string, error) {
+    // TODO: Implement OTP generation
+    // 1. Generate OTP token with expiry
+    // 2. Store mapping: token -> (url, msgType, msgID, expiry)
+    // 3. Create short URL with token
+    // 4. Return short URL
+
+    return url, nil // Currently pass-through
+}
+```
diff --git a/agent/output/adapters/openai/adapter.go b/agent/output/adapters/openai/adapter.go
new file mode 100644
index 00000000..3e434f34
--- /dev/null
+++ b/agent/output/adapters/openai/adapter.go
@@ -0,0 +1,91 @@
+package openai
+
+import "github.com/yaoapp/yao/agent/output/message"
+
+// Adapter is the OpenAI adapter that converts messages to OpenAI format
+type Adapter struct {
+	config   *AdapterConfig
+	registry *ConverterRegistry
+}
+
+// NewAdapter creates a new OpenAI adapter with default configuration
+func NewAdapter(options ...Option) *Adapter {
+	adapter := &Adapter{
+		config:   DefaultAdapterConfig(),
+		registry: NewConverterRegistry(),
+	}
+
+	// Apply options
+	for _, opt := range options {
+		opt(adapter)
+	}
+
+	return adapter
+}
+
+// Option is a function that configures the adapter
+type Option func(*Adapter)
+
+// WithBaseURL sets the base URL for generating view links
+func WithBaseURL(baseURL string) Option {
+	return func(a *Adapter) {
+		a.config.BaseURL = baseURL
+	}
+}
+
+// WithLinkTemplate sets a custom link template for a message type
+func WithLinkTemplate(msgType string, template string) Option {
+	return func(a *Adapter) {
+		a.config.LinkTemplates[msgType] = template
+	}
+}
+
+// WithLinkTransformer sets the link transformer function
+func WithLinkTransformer(transformer LinkTransformer) Option {
+	return func(a *Adapter) {
+		a.config.LinkTransformer = transformer
+	}
+}
+
+// WithModel sets the model name for OpenAI responses
+func WithModel(model string) Option {
+	return func(a *Adapter) {
+		a.config.Model = model
+	}
+}
+
+// WithConverter registers a custom converter for a message type
+func WithConverter(msgType string, converter ConverterFunc) Option {
+	return func(a *Adapter) {
+		a.registry.Register(msgType, converter)
+	}
+}
+
+// Adapt converts a universal Message to OpenAI-compatible format
+func (a *Adapter) Adapt(msg *message.Message) ([]interface{}, error) {
+	// Get converter for this message type
+	converter, exists := a.registry.GetConverter(msg.Type)
+	if !exists {
+		// Use default converter for unknown types (convert to link)
+		converter = convertToLink
+	}
+
+	// Convert the message
+	return converter(msg, a.config)
+}
+
+// SupportsType checks if the adapter explicitly supports a given message type
+func (a *Adapter) SupportsType(msgType string) bool {
+	_, exists := a.registry.GetConverter(msgType)
+	return exists
+}
+
+// GetConfig returns the adapter configuration
+func (a *Adapter) GetConfig() *AdapterConfig {
+	return a.config
+}
+
+// GetRegistry returns the converter registry
+func (a *Adapter) GetRegistry() *ConverterRegistry {
+	return a.registry
+}
diff --git a/agent/output/adapters/openai/converter.go b/agent/output/adapters/openai/converter.go
new file mode 100644
index 00000000..16d4cd5d
--- /dev/null
+++ b/agent/output/adapters/openai/converter.go
@@ -0,0 +1,260 @@
+package openai
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// ConverterRegistry manages message type converters
+type ConverterRegistry struct {
+	converters map[string]ConverterFunc
+}
+
+// NewConverterRegistry creates a new converter registry with default converters
+func NewConverterRegistry() *ConverterRegistry {
+	return &ConverterRegistry{
+		converters: map[string]ConverterFunc{
+			message.TypeText:     convertText,
+			message.TypeThinking: convertThinking,
+			message.TypeLoading:  convertLoading,
+			message.TypeToolCall: convertToolCall,
+			message.TypeError:    convertError,
+			message.TypeImage:    convertImage,
+			message.TypeAudio:    convertToLink,
+			message.TypeVideo:    convertToLink,
+			message.TypeAction:   convertAction,
+		},
+	}
+}
+
+// Register registers a custom converter for a message type
+func (r *ConverterRegistry) Register(msgType string, converter ConverterFunc) {
+	r.converters[msgType] = converter
+}
+
+// GetConverter retrieves a converter for a given message type.
+func (r *ConverterRegistry) GetConverter(msgType string) (ConverterFunc, bool) {
+	converter, exists := r.converters[msgType]
+	return converter, exists
+}
+
+// Convert converts a message using registered converters
+// If no converter is found, converts to link format
+func (r *ConverterRegistry) Convert(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	// Check for registered converter
+	if converter, exists := r.converters[msg.Type]; exists {
+		return converter(msg, config)
+	}
+
+	// Fallback: convert to link format
+	return convertToLink(msg, config)
+}
+
+// convertText converts text messages to OpenAI format
+func convertText(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	content := getStringProp(msg.Props, "content", "")
+
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"content": content,
+		}),
+	}, nil
+}
+
+// convertThinking converts thinking messages to OpenAI reasoning format (o1 series)
+func convertThinking(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	content := getStringProp(msg.Props, "content", "")
+
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"reasoning_content": content,
+		}),
+	}, nil
+}
+
+// convertLoading converts loading messages to OpenAI reasoning format
+// This makes loading messages visible in standard OpenAI clients as thinking process
+func convertLoading(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	message := getStringProp(msg.Props, "message", "Processing...")
+
+	// Convert loading to reasoning_content so it shows in OpenAI clients
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"reasoning_content": message,
+		}),
+	}, nil
+}
+
+// convertToolCall converts tool_call messages to OpenAI format
+func convertToolCall(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	// Tool call format varies, pass through the props
+	toolCalls := []map[string]interface{}{}
+
+	// If props contain tool call data, use it
+	if id, ok := msg.Props["id"].(string); ok {
+		toolCall := map[string]interface{}{
+			"id":   id,
+			"type": "function",
+		}
+
+		if function, ok := msg.Props["function"].(map[string]interface{}); ok {
+			toolCall["function"] = function
+		}
+
+		toolCalls = append(toolCalls, toolCall)
+	}
+
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"tool_calls": toolCalls,
+		}),
+	}, nil
+}
+
+// convertError converts error messages to OpenAI error format
+func convertError(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	message := getStringProp(msg.Props, "message", "An error occurred")
+	code := getStringProp(msg.Props, "code", "server_error")
+
+	return []interface{}{
+		map[string]interface{}{
+			"error": map[string]interface{}{
+				"message": message,
+				"type":    code,
+				"code":    code,
+			},
+		},
+	}, nil
+}
+
+// convertAction converts action messages to nothing (silent in OpenAI clients)
+// Action messages are system-level commands (open panel, navigate, etc.)
+// and should not be sent to standard chat clients
+func convertAction(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	// Return empty slice - no output for action messages in OpenAI format
+	return []interface{}{}, nil
+}
+
+// convertImage converts image messages to Markdown image format
+// Uses ![alt](url) which displays inline in Markdown-supporting clients
+func convertImage(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	// Get URL
+	url, ok := msg.Props["url"].(string)
+	if !ok || url == "" {
+		return nil, fmt.Errorf("image message missing url")
+	}
+
+	// Transform URL if transformer is provided
+	if config.LinkTransformer != nil {
+		transformedURL, err := config.LinkTransformer(url, msg.Type, msg.ID)
+		if err != nil {
+			return nil, err
+		}
+		url = transformedURL
+	}
+
+	// Get alt text (default to "Image")
+	alt := getStringProp(msg.Props, "alt", "Image")
+
+	// Format as Markdown image: ![alt](url)
+	template := getLinkTemplate(msg.Type, config)
+	text := fmt.Sprintf(template, alt, url)
+
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"content": text,
+		}),
+	}, nil
+}
+
+// convertToLink converts any message type to a Markdown link format
+func convertToLink(msg *message.Message, config *AdapterConfig) ([]interface{}, error) {
+	// Generate link
+	link, err := generateViewLink(msg, config)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get template
+	template := getLinkTemplate(msg.Type, config)
+
+	// Format text
+	var text string
+	if msg.Type == "button" {
+		// Button is special: needs button text
+		buttonText := getStringProp(msg.Props, "text", "Button")
+		text = fmt.Sprintf(template, buttonText, link)
+	} else {
+		text = fmt.Sprintf(template, link)
+	}
+
+	return []interface{}{
+		createOpenAIChunk(msg.ID, config.Model, map[string]interface{}{
+			"content": text,
+		}),
+	}, nil
+}
+
+// generateViewLink generates a view link for a message
+func generateViewLink(msg *message.Message, config *AdapterConfig) (string, error) {
+	// If Props contains a URL, use it
+	if url, ok := msg.Props["url"].(string); ok {
+		// Transform URL if transformer is provided
+		if config.LinkTransformer != nil {
+			return config.LinkTransformer(url, msg.Type, msg.ID)
+		}
+		return url, nil
+	}
+
+	// Generate view link: {baseURL}/agent/view/{type}/{id}
+	baseURL := config.BaseURL
+	if baseURL == "" {
+		baseURL = "" // TODO: Get from environment or context
+	}
+
+	viewURL := fmt.Sprintf("%s/agent/view/%s/%s", baseURL, msg.Type, msg.ID)
+
+	// Transform URL if transformer is provided
+	if config.LinkTransformer != nil {
+		return config.LinkTransformer(viewURL, msg.Type, msg.ID)
+	}
+
+	return viewURL, nil
+}
+
+// getLinkTemplate gets the link template for a message type
+func getLinkTemplate(msgType string, config *AdapterConfig) string {
+	if template, exists := config.LinkTemplates[msgType]; exists {
+		return template
+	}
+
+	// Default fallback template
+	return "📎 [View %s](" + msgType + ")"
+}
+
+// createOpenAIChunk creates an OpenAI chat completion chunk
+func createOpenAIChunk(id string, model string, delta map[string]interface{}) map[string]interface{} {
+	return map[string]interface{}{
+		"id":      id,
+		"object":  "chat.completion.chunk",
+		"created": time.Now().Unix(),
+		"model":   model,
+		"choices": []map[string]interface{}{
+			{
+				"index":         0,
+				"delta":         delta,
+				"finish_reason": nil,
+			},
+		},
+	}
+}
+
+// getStringProp safely gets a string property from props
+func getStringProp(props map[string]interface{}, key string, defaultValue string) string {
+	if val, ok := props[key].(string); ok {
+		return val
+	}
+	return defaultValue
+}
diff --git a/agent/output/adapters/openai/factory.go b/agent/output/adapters/openai/factory.go
new file mode 100644
index 00000000..eecb720e
--- /dev/null
+++ b/agent/output/adapters/openai/factory.go
@@ -0,0 +1,28 @@
+package openai
+
+import (
+	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// Factory is the factory for creating OpenAI writers and adapters
+type Factory struct {
+	options []Option
+}
+
+// NewFactory creates a new OpenAI factory with options
+func NewFactory(options ...Option) *Factory {
+	return &Factory{
+		options: options,
+	}
+}
+
+// CreateWriter creates an OpenAI writer
+func (f *Factory) CreateWriter(ctx *context.Context) (message.Writer, error) {
+	return NewWriter(ctx)
+}
+
+// CreateAdapter creates an OpenAI adapter
+func (f *Factory) CreateAdapter(ctx *context.Context) (message.Adapter, error) {
+	return NewAdapter(f.options...), nil
+}
diff --git a/agent/output/adapters/openai/types.go b/agent/output/adapters/openai/types.go
new file mode 100644
index 00000000..68df9429
--- /dev/null
+++ b/agent/output/adapters/openai/types.go
@@ -0,0 +1,62 @@
+package openai
+
+import "github.com/yaoapp/yao/agent/output/message"
+
+// ConverterFunc converts a message to OpenAI format chunks
+type ConverterFunc func(msg *message.Message, config *AdapterConfig) ([]interface{}, error)
+
+// LinkTransformer transforms a URL to a secure link (with OTP, short URL, etc.)
+// Returns the transformed link or error
+type LinkTransformer func(url string, msgType string, msgID string) (string, error)
+
+// AdapterConfig holds the configuration for OpenAI adapter
+type AdapterConfig struct {
+	// BaseURL is the base URL for generating view links
+	// Example: "https://api.example.com"
+	BaseURL string
+
+	// LinkTemplates defines the Markdown template for each message type
+	// %s will be replaced with the link
+	// Example: "🖼️ [View Image](%s)"
+	LinkTemplates map[string]string
+
+	// LinkTransformer transforms URLs to secure links with OTP
+	// If nil, URLs are used as-is
+	LinkTransformer LinkTransformer
+
+	// Model name to include in OpenAI responses
+	Model string
+}
+
+// DefaultLinkTemplates provides default Markdown templates for non-text message types
+var DefaultLinkTemplates = map[string]string{
+	"image":  "![%s](%s)",                 // Markdown image: ![alt](url) - displays inline
+	"audio":  "🔊 [Play Audio](%s)",      // Link (audio can't display inline in Markdown)
+	"video":  "🎬 [Watch Video](%s)",     // Link (video can't display inline in Markdown)
+	"file":   "📎 [Download File](%s)",
+	"page":   "📄 [Open Page](%s)",
+	"table":  "📊 [View Table](%s)",
+	"chart":  "📈 [View Chart](%s)",
+	"list":   "📋 [View List](%s)",
+	"form":   "📝 [Fill Form](%s)",
+	"button": "🔘 [%s](%s)", // Special: button needs two params (text, link)
+}
+
+// DefaultAdapterConfig returns a default adapter configuration
+func DefaultAdapterConfig() *AdapterConfig {
+	return &AdapterConfig{
+		BaseURL:         "", // Will be set from environment or context
+		LinkTemplates:   copyLinkTemplates(DefaultLinkTemplates),
+		LinkTransformer: nil, // No transformation by default
+		Model:           "yao-agent",
+	}
+}
+
+// copyLinkTemplates creates a copy of link templates
+func copyLinkTemplates(templates map[string]string) map[string]string {
+	copy := make(map[string]string, len(templates))
+	for k, v := range templates {
+		copy[k] = v
+	}
+	return copy
+}
diff --git a/agent/output/adapters/openai/writer.go b/agent/output/adapters/openai/writer.go
new file mode 100644
index 00000000..c570c027
--- /dev/null
+++ b/agent/output/adapters/openai/writer.go
@@ -0,0 +1,92 @@
+package openai
+
+import (
+	"encoding/json"
+
+	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// Writer implements the message.Writer interface for OpenAI-compatible clients
+type Writer struct {
+	ctx     *context.Context
+	adapter *Adapter
+}
+
+// NewWriter creates a new OpenAI writer
+func NewWriter(ctx *context.Context) (*Writer, error) {
+	// Create adapter with default config
+	adapter := NewAdapter()
+
+	return &Writer{
+		ctx:     ctx,
+		adapter: adapter,
+	}, nil
+}
+
+// Write writes a single message to the output stream
+func (w *Writer) Write(msg *message.Message) error {
+	// Convert message to OpenAI format using adapter
+	chunks, err := w.adapter.Adapt(msg)
+	if err != nil {
+		return err
+	}
+
+	// Send each chunk
+	for _, chunk := range chunks {
+		if err := w.sendChunk(chunk); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// WriteGroup writes a message group to the output stream
+func (w *Writer) WriteGroup(group *message.MessageGroup) error {
+	// For OpenAI, we don't send group markers
+	// Just send each message individually
+	for _, msg := range group.Messages {
+		if err := w.Write(msg); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Flush flushes any buffered data to the output stream
+func (w *Writer) Flush() error {
+	// For SSE, we don't need explicit flushing
+	// The underlying connection handles it
+	return nil
+}
+
+// Close closes the writer and cleans up resources
+func (w *Writer) Close() error {
+	// Send final [DONE] message for OpenAI compatibility
+	return w.sendDone()
+}
+
+// sendChunk sends a chunk to the output stream in SSE format
+func (w *Writer) sendChunk(chunk interface{}) error {
+	// Convert chunk to JSON
+	data, err := json.Marshal(chunk)
+	if err != nil {
+		return err
+	}
+
+	// Format as SSE: "data: {json}\n\n"
+	sseData := append([]byte("data: "), data...)
+	sseData = append(sseData, []byte("\n\n")...)
+
+	// Send via context's writer
+	return w.ctx.Send(sseData)
+}
+
+// sendDone sends the final [DONE] message
+func (w *Writer) sendDone() error {
+	// OpenAI SSE format uses "data: [DONE]\n\n" to signal completion
+	doneData := []byte("data: [DONE]\n\n")
+	return w.ctx.Send(doneData)
+}
diff --git a/agent/output/builtin.go b/agent/output/builtin.go
new file mode 100644
index 00000000..0932e0b1
--- /dev/null
+++ b/agent/output/builtin.go
@@ -0,0 +1,129 @@
+package output
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+// Helper functions for creating built-in message types
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+// NewTextMessage creates a text message
+func NewTextMessage(content string) *message.Message {
+	return &message.Message{
+		Type: message.TypeText,
+		Props: map[string]interface{}{
+			"content": content,
+		},
+	}
+}
+
+// NewThinkingMessage creates a thinking message
+func NewThinkingMessage(content string) *message.Message {
+	return &message.Message{
+		Type: message.TypeThinking,
+		Props: map[string]interface{}{
+			"content": content,
+		},
+	}
+}
+
+// NewLoadingMessage creates a loading message
+func NewLoadingMessage(msg string) *message.Message {
+	return &message.Message{
+		Type: message.TypeLoading,
+		Props: map[string]interface{}{
+			"message": msg,
+		},
+	}
+}
+
+// NewToolCallMessage creates a tool call message
+func NewToolCallMessage(id, name, arguments string) *message.Message {
+	return &message.Message{
+		Type: message.TypeToolCall,
+		Props: map[string]interface{}{
+			"id":        id,
+			"name":      name,
+			"arguments": arguments,
+		},
+	}
+}
+
+// NewErrorMessage creates an error message
+func NewErrorMessage(msg, code string) *message.Message {
+	return &message.Message{
+		Type: message.TypeError,
+		Props: map[string]interface{}{
+			"message": msg,
+			"code":    code,
+		},
+	}
+}
+
+// NewActionMessage creates an action message
+func NewActionMessage(name string, payload map[string]interface{}) *message.Message {
+	return &message.Message{
+		Type: message.TypeAction,
+		Props: map[string]interface{}{
+			"name":    name,
+			"payload": payload,
+		},
+	}
+}
+
+// NewImageMessage creates an image message
+func NewImageMessage(url string, alt string) *message.Message {
+	return &message.Message{
+		Type: message.TypeImage,
+		Props: map[string]interface{}{
+			"url": url,
+			"alt": alt,
+		},
+	}
+}
+
+// NewAudioMessage creates an audio message
+func NewAudioMessage(url string, format string) *message.Message {
+	return &message.Message{
+		Type: message.TypeAudio,
+		Props: map[string]interface{}{
+			"url":    url,
+			"format": format,
+		},
+	}
+}
+
+// NewVideoMessage creates a video message
+func NewVideoMessage(url string) *message.Message {
+	return &message.Message{
+		Type: message.TypeVideo,
+		Props: map[string]interface{}{
+			"url": url,
+		},
+	}
+}
+
+// IsBuiltinType checks if a message type is a built-in type
+func IsBuiltinType(msgType string) bool {
+	switch msgType {
+	case message.TypeText, message.TypeThinking, message.TypeLoading, message.TypeToolCall, message.TypeError, message.TypeImage, message.TypeAudio, message.TypeVideo, message.TypeAction:
+		return true
+	default:
+		return false
+	}
+}
+
+// GenerateID generates a unique message ID
+func GenerateID() string {
+	// Generate a random ID with timestamp prefix for uniqueness
+	timestamp := time.Now().UnixNano()
+	random := rand.Int63()
+	return fmt.Sprintf("msg_%d_%d", timestamp, random)
+}
diff --git a/agent/output/message/interfaces.go b/agent/output/message/interfaces.go
new file mode 100644
index 00000000..9ea46745
--- /dev/null
+++ b/agent/output/message/interfaces.go
@@ -0,0 +1,56 @@
+package message
+
+import "github.com/yaoapp/yao/agent/context"
+
+// Writer is the interface for writing output messages
+// Different writers handle different output formats (SSE, WebSocket, Standard, etc.)
+type Writer interface {
+	// Write writes a single message
+	Write(msg *Message) error
+
+	// WriteGroup writes a group of messages
+	WriteGroup(group *MessageGroup) error
+
+	// Flush flushes any buffered data
+	Flush() error
+
+	// Close closes the writer and releases resources
+	Close() error
+}
+
+// Adapter is the interface for adapting messages to different formats
+// Adapters transform messages from the universal DSL to specific client formats
+type Adapter interface {
+	// Adapt transforms a message to the target format
+	// Returns a slice of output chunks (some messages may be split into multiple chunks)
+	Adapt(msg *Message) ([]interface{}, error)
+
+	// SupportsType checks if this adapter supports a specific message type
+	SupportsType(msgType string) bool
+}
+
+// WriterFactory creates writers based on context
+type WriterFactory interface {
+	// NewWriter creates a writer for the given context
+	NewWriter(ctx *context.Context, adapter Adapter) (Writer, error)
+}
+
+// AdapterFactory creates adapters based on context
+type AdapterFactory interface {
+	// NewAdapter creates an adapter for the given context
+	NewAdapter(ctx *context.Context) (Adapter, error)
+}
+
+// StreamHandler handles streaming message processing
+// It bridges between LLM streaming chunks and output messages
+type StreamHandler interface {
+	// Handle processes a streaming chunk from LLM
+	Handle(chunkType context.StreamChunkType, data []byte) error
+
+	// Flush flushes any pending messages
+	Flush() error
+
+	// Close closes the handler
+	Close() error
+}
+
diff --git a/agent/output/message/types.go b/agent/output/message/types.go
new file mode 100644
index 00000000..6593b607
--- /dev/null
+++ b/agent/output/message/types.go
@@ -0,0 +1,158 @@
+package message
+
+// Message represents a universal message structure (DSL)
+// All messages are expressed through Type + Props, without predefining specific types
+type Message struct {
+	// Core fields
+	Type  string                 `json:"type"`            // Message type (frontend decides how to render)
+	Props map[string]interface{} `json:"props,omitempty"` // Message properties (passed to frontend component)
+
+	// Streaming control
+	ID    string `json:"id,omitempty"`    // Message ID (used for merging messages in streaming scenarios)
+	Delta bool   `json:"delta,omitempty"` // Whether this is an incremental update
+	Done  bool   `json:"done,omitempty"`  // Whether the message is complete
+
+	// Delta update control
+	DeltaPath   string `json:"delta_path,omitempty"`   // Update path (e.g., "content", "data", "items.0.name")
+	DeltaAction string `json:"delta_action,omitempty"` // Update action (append, replace, merge, set)
+
+	// Type correction (for streaming scenarios)
+	TypeChange bool `json:"type_change,omitempty"` // Marks this as a type correction message
+
+	// Message group
+	GroupID    string `json:"group_id,omitempty"`    // Parent message group ID
+	GroupStart bool   `json:"group_start,omitempty"` // Marks the start of a message group
+	GroupEnd   bool   `json:"group_end,omitempty"`   // Marks the end of a message group
+
+	// Metadata
+	Metadata *Metadata `json:"metadata,omitempty"` // Additional metadata
+}
+
+// Metadata represents message metadata
+type Metadata struct {
+	Timestamp int64  `json:"timestamp,omitempty"` // Timestamp in nanoseconds
+	Sequence  int    `json:"sequence,omitempty"`  // Sequence number (for ordering)
+	TraceID   string `json:"trace_id,omitempty"`  // Trace ID (for debugging)
+}
+
+// MessageGroup represents a semantically complete group of messages
+type MessageGroup struct {
+	ID       string     `json:"id"`                 // Message group ID
+	Messages []*Message `json:"messages"`           // List of messages
+	Metadata *Metadata  `json:"metadata,omitempty"` // Metadata
+}
+
+// Built-in message types that all adapters must support
+// These types have standardized Props structures
+const (
+	// Content types
+	TypeText     = "text"      // Plain text or Markdown content
+	TypeThinking = "thinking"  // Reasoning/thinking process (e.g., o1 models)
+	TypeLoading  = "loading"   // Loading/processing indicator (preprocessing, knowledge base search, etc.)
+	TypeToolCall = "tool_call" // LLM tool/function call
+	TypeError    = "error"     // Error message
+
+	// Media types (with OpenAI support)
+	TypeImage = "image" // Image content
+	TypeAudio = "audio" // Audio content
+	TypeVideo = "video" // Video content
+
+	// System types (not visible in standard chat clients)
+	TypeAction = "action" // System action (open panel, navigate, etc.) - silent in OpenAI clients
+)
+
+// Standard Props structures for built-in types
+
+// TextProps defines the standard structure for text messages
+// Type: "text"
+// Props: {"content": string}
+type TextProps struct {
+	Content string `json:"content"` // Text content (supports Markdown)
+}
+
+// ThinkingProps defines the standard structure for thinking messages
+// Type: "thinking"
+// Props: {"content": string}
+type ThinkingProps struct {
+	Content string `json:"content"` // Reasoning/thinking content
+}
+
+// LoadingProps defines the standard structure for loading messages
+// Type: "loading"
+// Props: {"message": string}
+type LoadingProps struct {
+	Message string `json:"message"` // Loading message (e.g., "Searching knowledge base...")
+}
+
+// ToolCallProps defines the standard structure for tool_call messages
+// Type: "tool_call"
+// Props: {"id": string, "name": string, "arguments": string}
+type ToolCallProps struct {
+	ID        string `json:"id"`                  // Tool call ID
+	Name      string `json:"name"`                // Function/tool name
+	Arguments string `json:"arguments,omitempty"` // JSON string of arguments
+}
+
+// ErrorProps defines the standard structure for error messages
+// Type: "error"
+// Props: {"message": string, "code": string}
+type ErrorProps struct {
+	Message string `json:"message"`           // Error message
+	Code    string `json:"code,omitempty"`    // Error code
+	Details string `json:"details,omitempty"` // Additional error details
+}
+
+// ActionProps defines the standard structure for action messages
+// Type: "action"
+// Props: {"name": string, "payload": map}
+type ActionProps struct {
+	Name    string                 `json:"name"`              // Action name (e.g., "open_panel", "navigate")
+	Payload map[string]interface{} `json:"payload,omitempty"` // Action payload/parameters
+}
+
+// ImageProps defines the standard structure for image messages
+// Type: "image"
+// Props: {"url": string, "alt": string, "width": int, "height": int, "detail": string}
+type ImageProps struct {
+	URL    string `json:"url"`              // Required: Image URL or base64 encoded data
+	Alt    string `json:"alt,omitempty"`    // Alternative text
+	Width  int    `json:"width,omitempty"`  // Image width in pixels
+	Height int    `json:"height,omitempty"` // Image height in pixels
+	Detail string `json:"detail,omitempty"` // OpenAI detail level: "auto", "low", "high"
+}
+
+// AudioProps defines the standard structure for audio messages
+// Type: "audio"
+// Props: {"url": string, "format": string, "duration": float64, "transcript": string, "autoplay": bool}
+type AudioProps struct {
+	URL        string  `json:"url"`                  // Required: Audio URL or base64 encoded data
+	Format     string  `json:"format,omitempty"`     // Audio format: "mp3", "wav", "ogg", etc.
+	Duration   float64 `json:"duration,omitempty"`   // Duration in seconds
+	Transcript string  `json:"transcript,omitempty"` // Audio transcript text
+	Autoplay   bool    `json:"autoplay,omitempty"`   // Whether to autoplay
+	Controls   bool    `json:"controls,omitempty"`   // Whether to show controls (default: true)
+}
+
+// VideoProps defines the standard structure for video messages
+// Type: "video"
+// Props: {"url": string, "format": string, "duration": float64, "thumbnail": string, "width": int, "height": int, "autoplay": bool}
+type VideoProps struct {
+	URL       string  `json:"url"`                 // Required: Video URL
+	Format    string  `json:"format,omitempty"`    // Video format: "mp4", "webm", etc.
+	Duration  float64 `json:"duration,omitempty"`  // Duration in seconds
+	Thumbnail string  `json:"thumbnail,omitempty"` // Thumbnail/poster image URL
+	Width     int     `json:"width,omitempty"`     // Video width in pixels
+	Height    int     `json:"height,omitempty"`    // Video height in pixels
+	Autoplay  bool    `json:"autoplay,omitempty"`  // Whether to autoplay
+	Controls  bool    `json:"controls,omitempty"`  // Whether to show controls (default: true)
+	Loop      bool    `json:"loop,omitempty"`      // Whether to loop
+}
+
+// Delta action constants for incremental updates
+const (
+	DeltaAppend  = "append"  // Append (for arrays, strings)
+	DeltaReplace = "replace" // Replace (for any value)
+	DeltaMerge   = "merge"   // Merge (for objects)
+	DeltaSet     = "set"     // Set (for new fields)
+)
+
diff --git a/agent/output/output.go b/agent/output/output.go
index ad89311b..65aa99f0 100644
--- a/agent/output/output.go
+++ b/agent/output/output.go
@@ -1 +1,149 @@
 package output
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/yaoapp/yao/agent/context"
+	"github.com/yaoapp/yao/agent/output/adapters/cui"
+	"github.com/yaoapp/yao/agent/output/adapters/openai"
+	"github.com/yaoapp/yao/agent/output/message"
+)
+
+var (
+	writerCache   = make(map[*context.Context]message.Writer)
+	writerMutex   sync.RWMutex
+	globalFactory message.WriterFactory
+)
+
+// Send sends a single message using the appropriate writer for the context
+func Send(ctx *context.Context, msg *message.Message) error {
+	writer, err := GetWriter(ctx)
+	if err != nil {
+		return err
+	}
+	return writer.Write(msg)
+}
+
+// SendGroup sends a message group using the appropriate writer for the context
+func SendGroup(ctx *context.Context, group *message.MessageGroup) error {
+	writer, err := GetWriter(ctx)
+	if err != nil {
+		return err
+	}
+	return writer.WriteGroup(group)
+}
+
+// GetWriter gets or creates a writer for the given context
+// Writers are cached per context to avoid recreating them
+func GetWriter(ctx *context.Context) (message.Writer, error) {
+	// Try to get cached writer
+	writerMutex.RLock()
+	writer, exists := writerCache[ctx]
+	writerMutex.RUnlock()
+
+	if exists {
+		return writer, nil
+	}
+
+	// Create new writer
+	writerMutex.Lock()
+	defer writerMutex.Unlock()
+
+	// Double-check after acquiring write lock
+	if writer, exists := writerCache[ctx]; exists {
+		return writer, nil
+	}
+
+	// Create writer based on context.Accept
+	writer, err := createWriter(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	// Cache the writer
+	writerCache[ctx] = writer
+
+	return writer, nil
+}
+
+// createWriter creates a writer based on context.Accept
+func createWriter(ctx *context.Context) (message.Writer, error) {
+	// If global factory is set, use it
+	if globalFactory != nil {
+		return globalFactory.NewWriter(ctx, nil)
+	}
+
+	// Default: create based on Accept type
+	switch ctx.Accept {
+	case context.AcceptStandard:
+		// OpenAI-compatible format
+		return openai.NewWriter(ctx)
+
+	case context.AcceptWebCUI, context.AccepNativeCUI, context.AcceptDesktopCUI:
+		// CUI format
+		return cui.NewWriter(ctx)
+
+	default:
+		// Default to CUI
+		return cui.NewWriter(ctx)
+	}
+}
+
+// SetWriterFactory sets a custom writer factory
+// This allows applications to provide their own writer implementations
+func SetWriterFactory(factory message.WriterFactory) {
+	globalFactory = factory
+}
+
+// ClearWriterCache clears the writer cache
+// Should be called when contexts are cleaned up
+func ClearWriterCache(ctx *context.Context) {
+	writerMutex.Lock()
+	defer writerMutex.Unlock()
+	delete(writerCache, ctx)
+}
+
+// ClearAllWriterCache clears all cached writers
+func ClearAllWriterCache() {
+	writerMutex.Lock()
+	defer writerMutex.Unlock()
+	writerCache = make(map[*context.Context]message.Writer)
+}
+
+// Flush flushes the writer for the given context
+func Flush(ctx *context.Context) error {
+	writer, err := GetWriter(ctx)
+	if err != nil {
+		return err
+	}
+	return writer.Flush()
+}
+
+// Close closes the writer for the given context and removes it from cache
+func Close(ctx *context.Context) error {
+	writer, err := GetWriter(ctx)
+	if err != nil {
+		return err
+	}
+
+	err = writer.Close()
+	ClearWriterCache(ctx)
+	return err
+}
+
+// SendMulti is a convenience function to send multiple messages
+func SendMulti(ctx *context.Context, messages ...*message.Message) error {
+	writer, err := GetWriter(ctx)
+	if err != nil {
+		return err
+	}
+
+	for _, msg := range messages {
+		if err := writer.Write(msg); err != nil {
+			return fmt.Errorf("failed to send message: %w", err)
+		}
+	}
+
+	return nil
+}