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Architecture Overview

Open Brain is a single Python MCP server (server.py) backed by PostgreSQL + pgvector. It exposes 11 tools over stdio or HTTP that any MCP-compatible AI client can call.

System Diagram

graph TD
    A[Your thought / conversation] --> B[remember / capture_context]
    B --> C[Ollama or OpenAI<br/>Vector Embedding]
    B --> D[Heuristic or LLM<br/>Metadata Extraction]
    B --> E[Project Scoping]
    C --> F[(PostgreSQL + pgvector)]
    D --> F
    E --> F
    F --> G[MCP Server<br/>stdio / HTTP]
    G --> H[Claude Code]
    G --> I[Cursor]
    G --> J[Windsurf]
    G --> K[VS Code Copilot]
    G --> L[ChatGPT Desktop]
    G --> M[Any MCP Client]

Data Flow

Writing (Capture)

  1. An agent calls remember (single fact) or capture_context (session text)
  2. capture_context optionally decomposes the text into atomic memories via a local LLM
  3. Each memory is embedded via Ollama or OpenAI
  4. Metadata is extracted (type, people, topics, action items) via heuristic or LLM
  5. Deduplication check: if a near-identical memory exists (cosine similarity >= 0.92), skip or update
  6. Stored in PostgreSQL with the embedding vector, metadata JSONB, and project tag

Reading (Recall)

  1. An agent calls search with a natural language query
  2. The query is embedded using the same model
  3. pgvector finds the nearest neighbors via HNSW index
  4. Results are filtered by type, people, or project if specified
  5. Previews (200 chars) are returned to save tokens
  6. The agent calls recall with specific IDs to get full content

Components

Component Technology Purpose
MCP Server Python + FastMCP Exposes 11 tools over stdio/HTTP
Database PostgreSQL 16 + pgvector Vector storage, JSONB metadata, full SQL
Vector Index HNSW (m=16, ef=64) Fast approximate nearest-neighbor search
Embeddings Ollama (nomic-embed-text) 768-dim dense vectors, runs locally
Metadata LLM Ollama (qwen2.5:32b) Rich extraction of people, topics, types
Wire CLI Python (wire.py) Auto-discovers and configures MCP clients

File Structure

open-brain/
├── server.py               # MCP server, 11 tools
├── wire.py                 # Agent auto-discovery + wiring CLI
├── requirements.txt        # Python dependencies
├── test_server.py          # End-to-end test suite
├── docker-compose.yml      # PostgreSQL + pgvector
├── .env.example            # Config template
├── prompts/
│   ├── windsurf-rules.md   # Auto-capture rules for Windsurf
│   ├── cursor-rules.md     # Auto-capture rules for Cursor
│   ├── claude-desktop.md   # System prompt for Claude Desktop
│   └── generic-system-prompt.md
└── scripts/
    ├── setup_db.py         # One-time DB initialization
    ├── migrate_v2.py       # v1 -> v2 schema migration
    └── ensure-stack.sh     # Verify/start Ollama + DB (WSL)

Cost

Component Monthly Cost
PostgreSQL + pgvector (Docker) $0
Ollama embeddings (local) $0
Ollama metadata LLM (local) $0
OpenAI embeddings (if used) ~$0.10-$0.30
Total (local stack) ~$0/month