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This document provides a comprehensive overview of the DeerFlow backend architecture.
## System Architecture
```
┌──────────────────────────────────────────────────────────────────────────┐
│ Client (Browser) │
└─────────────────────────────────┬────────────────────────────────────────┘
│
▼
┌──────────────────────────────────────────────────────────────────────────┐
│ Nginx (Port 2026) │
│ Unified Reverse Proxy Entry Point │
│ ┌────────────────────────────────────────────────────────────────────┐ │
│ │ /api/langgraph/* → LangGraph Server (2024) │ │
│ │ /api/* → Gateway API (8001) │ │
│ │ /* → Frontend (3000) │ │
│ └────────────────────────────────────────────────────────────────────┘ │
└─────────────────────────────────┬────────────────────────────────────────┘
│
┌───────────────────────┼───────────────────────┐
│ │ │
▼ ▼ ▼
┌─────────────────────┐ ┌─────────────────────┐ ┌─────────────────────┐
│ LangGraph Server │ │ Gateway API │ │ Frontend │
│ (Port 2024) │ │ (Port 8001) │ │ (Port 3000) │
│ │ │ │ │ │
│ - Agent Runtime │ │ - Models API │ │ - Next.js App │
│ - Thread Mgmt │ │ - MCP Config │ │ - React UI │
│ - SSE Streaming │ │ - Skills Mgmt │ │ - Chat Interface │
│ - Checkpointing │ │ - File Uploads │ │ │
│ │ │ - Artifacts │ │ │
└─────────────────────┘ └─────────────────────┘ └─────────────────────┘
│ │
│ ┌─────────────────┘
│ │
▼ ▼
┌──────────────────────────────────────────────────────────────────────────┐
│ Shared Configuration │
│ ┌─────────────────────────┐ ┌────────────────────────────────────────┐ │
│ │ config.yaml │ │ extensions_config.json │ │
│ │ - Models │ │ - MCP Servers │ │
│ │ - Tools │ │ - Skills State │ │
│ │ - Sandbox │ │ │ │
│ │ - Summarization │ │ │ │
│ └─────────────────────────┘ └────────────────────────────────────────┘ │
└──────────────────────────────────────────────────────────────────────────┘
```
## Component Details
### LangGraph Server
The LangGraph server is the core agent runtime, built on LangGraph for robust multi-agent workflow orchestration.
**Entry Point**: `src/agents/lead_agent/agent.py:make_lead_agent`
**Key Responsibilities**:
- Agent creation and configuration
- Thread state management
- Middleware chain execution
- Tool execution orchestration
- SSE streaming for real-time responses
**Configuration**: `langgraph.json`
```json
{
"agent": {
"type": "agent",
"path": "src.agents:make_lead_agent"
}
}
```
### Gateway API
FastAPI application providing REST endpoints for non-agent operations.
**Entry Point**: `src/gateway/app.py`
**Routers**:
- `models.py` - `/api/models` - Model listing and details
- `mcp.py` - `/api/mcp` - MCP server configuration
- `skills.py` - `/api/skills` - Skills management
- `uploads.py` - `/api/threads/{id}/uploads` - File upload
- `artifacts.py` - `/api/threads/{id}/artifacts` - Artifact serving
### Agent Architecture
```
┌─────────────────────────────────────────────────────────────────────────┐
│ make_lead_agent(config) │
└────────────────────────────────────┬────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────────────┐
│ Middleware Chain │
│ ┌──────────────────────────────────────────────────────────────────┐ │
│ │ 1. ThreadDataMiddleware - Initialize workspace/uploads/outputs │ │
│ │ 2. UploadsMiddleware - Process uploaded files │ │
│ │ 3. SandboxMiddleware - Acquire sandbox environment │ │
│ │ 4. SummarizationMiddleware - Context reduction (if enabled) │ │
│ │ 5. TitleMiddleware - Auto-generate titles │ │
│ │ 6. TodoListMiddleware - Task tracking (if plan_mode) │ │
│ │ 7. ViewImageMiddleware - Vision model support │ │
│ │ 8. ClarificationMiddleware - Handle clarifications │ │
│ └──────────────────────────────────────────────────────────────────┘ │
└────────────────────────────────────┬────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────────────┐
│ Agent Core │
│ ┌──────────────────┐ ┌──────────────────┐ ┌──────────────────────┐ │
│ │ Model │ │ Tools │ │ System Prompt │ │
│ │ (from factory) │ │ (configured + │ │ (with skills) │ │
│ │ │ │ MCP + builtin) │ │ │ │
│ └──────────────────┘ └──────────────────┘ └──────────────────────┘ │
└─────────────────────────────────────────────────────────────────────────┘
```
### Thread State
The `ThreadState` extends LangGraph's `AgentState` with additional fields:
```python
class ThreadState(AgentState):
# Core state from AgentState
messages: list[BaseMessage]
# DeerFlow extensions
sandbox: dict # Sandbox environment info
artifacts: list[str] # Generated file paths
thread_data: dict # {workspace, uploads, outputs} paths
title: str | None # Auto-generated conversation title
todos: list[dict] # Task tracking (plan mode)
viewed_images: dict # Vision model image data
```
### Sandbox System
```
┌─────────────────────────────────────────────────────────────────────────┐
│ Sandbox Architecture │
└─────────────────────────────────────────────────────────────────────────┘
┌─────────────────────────┐
│ SandboxProvider │ (Abstract)
│ - acquire() │
│ - get() │
│ - release() │
└────────────┬────────────┘
│
┌────────────────────┼────────────────────┐
│ │
▼ ▼
┌─────────────────────────┐ ┌─────────────────────────┐
│ LocalSandboxProvider │ │ AioSandboxProvider │
│ (src/sandbox/local.py) │ │ (src/community/) │
│ │ │ │
│ - Singleton instance │ │ - Docker-based │
│ - Direct execution │ │ - Isolated containers │
│ - Development use │ │ - Production use │
└─────────────────────────┘ └─────────────────────────┘
┌─────────────────────────┐
│ Sandbox │ (Abstract)
│ - execute_command() │
│ - read_file() │
│ - write_file() │
│ - list_dir() │
└─────────────────────────┘
```
**Virtual Path Mapping**:
| Virtual Path | Physical Path |
|-------------|---------------|
| `/mnt/user-data/workspace` | `backend/.deer-flow/threads/{thread_id}/user-data/workspace` |
| `/mnt/user-data/uploads` | `backend/.deer-flow/threads/{thread_id}/user-data/uploads` |
| `/mnt/user-data/outputs` | `backend/.deer-flow/threads/{thread_id}/user-data/outputs` |
| `/mnt/skills` | `deer-flow/skills/` |
### Tool System
```
┌─────────────────────────────────────────────────────────────────────────┐
│ Tool Sources │
└─────────────────────────────────────────────────────────────────────────┘
┌─────────────────────┐ ┌─────────────────────┐ ┌─────────────────────┐
│ Built-in Tools │ │ Configured Tools │ │ MCP Tools │
│ (src/tools/) │ │ (config.yaml) │ │ (extensions.json) │
├─────────────────────┤ ├─────────────────────┤ ├─────────────────────┤
│ - present_file │ │ - web_search │ │ - github │
│ - ask_clarification │ │ - web_fetch │ │ - filesystem │
│ - view_image │ │ - bash │ │ - postgres │
│ │ │ - read_file │ │ - brave-search │
│ │ │ - write_file │ │ - puppeteer │
│ │ │ - str_replace │ │ - ... │
│ │ │ - ls │ │ │
└─────────────────────┘ └─────────────────────┘ └─────────────────────┘
│ │ │
└───────────────────────┴───────────────────────┘
│
▼
┌─────────────────────────┐
│ get_available_tools() │
│ (src/tools/__init__) │
└─────────────────────────┘
```
### Model Factory
```
┌─────────────────────────────────────────────────────────────────────────┐
│ Model Factory │
│ (src/models/factory.py) │
└─────────────────────────────────────────────────────────────────────────┘
config.yaml:
┌─────────────────────────────────────────────────────────────────────────┐
│ models: │
│ - name: gpt-4 │
│ display_name: GPT-4 │
│ use: langchain_openai:ChatOpenAI │
│ model: gpt-4 │
│ api_key: $OPENAI_API_KEY │
│ max_tokens: 4096 │
│ supports_thinking: false │
│ supports_vision: true │
└─────────────────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────────┐
│ create_chat_model() │
│ - name: str │
│ - thinking_enabled │
└────────────┬────────────┘
│
▼
┌─────────────────────────┐
│ resolve_class() │
│ (reflection system) │
└────────────┬────────────┘
│
▼
┌─────────────────────────┐
│ BaseChatModel │
│ (LangChain instance) │
└─────────────────────────┘
```
**Supported Providers**:
- OpenAI (`langchain_openai:ChatOpenAI`)
- Anthropic (`langchain_anthropic:ChatAnthropic`)
- DeepSeek (`langchain_deepseek:ChatDeepSeek`)
- Custom via LangChain integrations
### MCP Integration
```
┌─────────────────────────────────────────────────────────────────────────┐
│ MCP Integration │
│ (src/mcp/manager.py) │
└─────────────────────────────────────────────────────────────────────────┘
extensions_config.json:
┌─────────────────────────────────────────────────────────────────────────┐
│ { │
│ "mcpServers": { │
│ "github": { │
│ "enabled": true, │
│ "type": "stdio", │
│ "command": "npx", │
│ "args": ["-y", "@modelcontextprotocol/server-github"], │
│ "env": {"GITHUB_TOKEN": "$GITHUB_TOKEN"} │
│ } │
│ } │
│ } │
└─────────────────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────────┐
│ MultiServerMCPClient │
│ (langchain-mcp-adapters)│
└────────────┬────────────┘
│
┌────────────────────┼────────────────────┐
│ │ │
▼ ▼ ▼
┌───────────┐ ┌───────────┐ ┌───────────┐
│ stdio │ │ SSE │ │ HTTP │
│ transport │ │ transport │ │ transport │
└───────────┘ └───────────┘ └───────────┘
```
### Skills System
```
┌─────────────────────────────────────────────────────────────────────────┐
│ Skills System │
│ (src/skills/loader.py) │
└─────────────────────────────────────────────────────────────────────────┘
Directory Structure:
┌─────────────────────────────────────────────────────────────────────────┐
│ skills/ │
│ ├── public/ # Public skills (committed) │
│ │ ├── pdf-processing/ │
│ │ │ └── SKILL.md │
│ │ ├── frontend-design/ │
│ │ │ └── SKILL.md │
│ │ └── ... │
│ └── custom/ # Custom skills (gitignored) │
│ └── user-installed/ │
│ └── SKILL.md │
└─────────────────────────────────────────────────────────────────────────┘
SKILL.md Format:
┌─────────────────────────────────────────────────────────────────────────┐
│ --- │
│ name: PDF Processing │
│ description: Handle PDF documents efficiently │
│ license: MIT │
│ allowed-tools: │
│ - read_file │
│ - write_file │
│ - bash │
│ --- │
│ │
│ # Skill Instructions │
│ Content injected into system prompt... │
└─────────────────────────────────────────────────────────────────────────┘
```
### Request Flow
```
┌─────────────────────────────────────────────────────────────────────────┐
│ Request Flow Example │
│ User sends message to agent │
└─────────────────────────────────────────────────────────────────────────┘
1. Client → Nginx
POST /api/langgraph/threads/{thread_id}/runs
{"input": {"messages": [{"role": "user", "content": "Hello"}]}}
2. Nginx → LangGraph Server (2024)
Proxied to LangGraph server
3. LangGraph Server
a. Load/create thread state
b. Execute middleware chain:
- ThreadDataMiddleware: Set up paths
- UploadsMiddleware: Inject file list
- SandboxMiddleware: Acquire sandbox
- SummarizationMiddleware: Check token limits
- TitleMiddleware: Generate title if needed
- TodoListMiddleware: Load todos (if plan mode)
- ViewImageMiddleware: Process images
- ClarificationMiddleware: Check for clarifications
c. Execute agent:
- Model processes messages
- May call tools (bash, web_search, etc.)
- Tools execute via sandbox
- Results added to messages
d. Stream response via SSE
4. Client receives streaming response
```
## Data Flow
### File Upload Flow
```
1. Client uploads file
POST /api/threads/{thread_id}/uploads
Content-Type: multipart/form-data
2. Gateway receives file
- Validates file
- Stores in .deer-flow/threads/{thread_id}/user-data/uploads/
- If document: converts to Markdown via markitdown
3. Returns response
{
"files": [{
"filename": "doc.pdf",
"path": ".deer-flow/.../uploads/doc.pdf",
"virtual_path": "/mnt/user-data/uploads/doc.pdf",
"artifact_url": "/api/threads/.../artifacts/mnt/.../doc.pdf"
}]
}
4. Next agent run
- UploadsMiddleware lists files
- Injects file list into messages
- Agent can access via virtual_path
```
### Configuration Reload
```
1. Client updates MCP config
PUT /api/mcp/config
2. Gateway writes extensions_config.json
- Updates mcpServers section
- File mtime changes
3. MCP Manager detects change
- get_cached_mcp_tools() checks mtime
- If changed: reinitializes MCP client
- Loads updated server configurations
4. Next agent run uses new tools
```
## Security Considerations
### Sandbox Isolation
- Agent code executes within sandbox boundaries
- Local sandbox: Direct execution (development only)
- Docker sandbox: Container isolation (production recommended)
- Path traversal prevention in file operations
### API Security
- Thread isolation: Each thread has separate data directories
- File validation: Uploads checked for path safety
- Environment variable resolution: Secrets not stored in config
### MCP Security
- Each MCP server runs in its own process
- Environment variables resolved at runtime
- Servers can be enabled/disabled independently
## Performance Considerations
### Caching
- MCP tools cached with file mtime invalidation
- Configuration loaded once, reloaded on file change
- Skills parsed once at startup, cached in memory
### Streaming
- SSE used for real-time response streaming
- Reduces time to first token
- Enables progress visibility for long operations
### Context Management
- Summarization middleware reduces context when limits approached
- Configurable triggers: tokens, messages, or fraction
- Preserves recent messages while summarizing older ones
|