open-brain-mcp

A self-hosted second brain MCP server — capture thoughts from any MCP client, search them semantically, keep everything on hardware you control.

Inspired by Nate B. Jones's Open Brain (OB1), rebuilt with zero required cloud AI dependencies: local Postgres + pgvector, local fastembed embeddings (BAAI/bge-small-en-v1.5, 384-dim). No Supabase, no hosted embedding API required for core operation.

Project state (2026-07-20): usable alpha / production-personal.
Running in production on a single VM for Miss Minutes (Hermes agent) with optional claude.ai remote connector. API surface is stable enough for daily use; expect small breaking changes until 1.0. Not a multi-tenant SaaS.

Current status

Architecture in one line: one Postgres database on your server; every agent (Hermes, Claude Code, claude.ai, OpenCode, …) is just an MCP client.

Claude.ai ──HTTP MCP──┐
Hermes/Discord ─stdio─┼──► open-brain-mcp ──► Postgres+pgvector (you host)
Laptop agent ──stdio/TS┘

Related MCP server: personal-knowledge

Tools

Requirements

• Python 3.11+

• Postgres 15+ with pgvector

• ~500MB+ RAM for embedding model once loaded

Database

sudo -u postgres psql -c "CREATE USER openbrain WITH PASSWORD '…';"
sudo -u postgres psql -c "CREATE DATABASE openbrain OWNER openbrain;"
sudo -u postgres psql -d openbrain -c "CREATE EXTENSION IF NOT EXISTS vector;"

Minimal schema (384-dim):

CREATE TABLE IF NOT EXISTS thoughts (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  content TEXT NOT NULL,
  metadata JSONB NOT NULL DEFAULT '{}',
  fingerprint TEXT,
  embedding vector(384),
  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
CREATE UNIQUE INDEX IF NOT EXISTS thoughts_fingerprint_uidx ON thoughts (fingerprint)
  WHERE fingerprint IS NOT NULL;
CREATE INDEX IF NOT EXISTS thoughts_embedding_ivfflat ON thoughts
  USING ivfflat (embedding vector_cosine_ops) WITH (lists = 100);

-- similarity helper used by search (cosine distance)
CREATE OR REPLACE FUNCTION match_thoughts(
  query_embedding vector(384),
  match_threshold float DEFAULT 0.35,
  match_count int DEFAULT 8,
  metadata_filter jsonb DEFAULT '{}'::jsonb
) RETURNS TABLE (
  id uuid,
  content text,
  metadata jsonb,
  created_at timestamptz,
  similarity float
) LANGUAGE sql STABLE AS $$
  SELECT t.id, t.content, t.metadata, t.created_at,
         1 - (t.embedding <=> query_embedding) AS similarity
  FROM thoughts t
  WHERE t.embedding IS NOT NULL
    AND 1 - (t.embedding <=> query_embedding) >= match_threshold
    AND (metadata_filter = '{}'::jsonb OR t.metadata @> metadata_filter)
  ORDER BY t.embedding <=> query_embedding
  LIMIT match_count;
$$;

If your live DB already has a compatible match_thoughts / thoughts schema from an earlier OB1-inspired setup, keep it — adjust only if dimensions differ.

Install

git clone https://github.com/lazo99/open-brain-mcp.git
cd open-brain-mcp
python3 -m venv .venv
.venv/bin/pip install -r requirements.txt

Credentials (never commit):

# ~/.secrets/open-brain.env
DATABASE_URL=postgresql://openbrain:***@127.0.0.1:5432/openbrain
OPEN_BRAIN_EMBED_MODEL=BAAI/bge-small-en-v1.5
# HTTP / claude.ai only:
OPEN_BRAIN_REMOTE_SECRET=long-random-string
# optional convenience:
# OPEN_BRAIN_REMOTE_URL=https://brain.example.com/<secret>/mcp

Run

stdio (Hermes, Claude Code, OpenCode, Cursor, …)

./run.sh
# or:
claude mcp add open-brain -- /path/to/open-brain-mcp/run.sh

run.sh sources ~/.secrets/open-brain.env when present.

HTTP for claude.ai (server_http.py)

Minimal streamable-HTTP surface (capture_thought + search_thoughts only).

• Listens on 127.0.0.1:8090

• MCP path: /{OPEN_BRAIN_REMOTE_SECRET}/mcp

• Put a reverse proxy or Cloudflare Tunnel in front (e.g. brain.example.com)

• The URL path is the credential (claude.ai custom connectors typically cannot set arbitrary auth headers)

export DATABASE_URL=…
export OPEN_BRAIN_REMOTE_SECRET=…
.venv/bin/python server_http.py

In claude.ai: Settings → Connectors → add remote MCP → paste:

https://brain.example.com/<OPEN_BRAIN_REMOTE_SECRET>/mcp

Remote stdio (second machine)

Keep Postgres bound to localhost. Bridge with SSH/Tailscale:

#!/usr/bin/env bash
exec ssh user@your-vm '~/Code/open-brain-mcp/run.sh'

Register that script as the MCP command on the laptop.

Production notes (reference deployment)

Personal production pattern used by the author:

• Single GCP VM, Postgres local, Tailscale for admin

• open-brain-web.service runs HTTP MCP as a locked-down user

• Cloudflare Tunnel hostname → 127.0.0.1:8090

• Hermes Agent on the same VM uses stdio MCP for full tools

• claude.ai uses HTTP MCP for capture/search only

• Secrets: env files + password manager + optional cloud secret manager — not git

Security

• Treat HTTP secret URLs like passwords; rotate if leaked

• Prefer localhost + tunnel over public bind

• DB user should only need rights on thoughts (+ sequence/functions used)

• Do not log request URLs that contain the secret path

Roadmap (honest)

• Packaged SQL migration files in-repo

• Optional token header auth if/when claude.ai supports it cleanly

• Obsidian plugin or documented ingest recipe

• Metrics / backup docs

• 1.0 when schema + HTTP auth story freeze

License

MIT

Related

• Upstream idea: OB1

• This repo: https://github.com/lazo99/open-brain-mcp