brain-mcp

An MCP (Model Context Protocol) server that provides persistent semantic memory backed by PostgreSQL + pgvector. Store "thoughts" with vector embeddings and organize them via a flexible dimensional model.

Two Servers

This repo provides two MCP servers with a shared codebase:

• brain-mcp (dist/index.js) — General-purpose knowledge store with ADR support. Use this for non-code contexts.

• brain-code-mcp (dist/code.js) — Superset of brain-mcp with code-aware tools. Use this for software projects.

You only need to configure one — brain-code-mcp includes all brain-mcp tools.

Related MCP server: persistent-memory

Features

• Semantic search — find thoughts by meaning using cosine similarity over vector embeddings

• Dimensional organization — tag thoughts with typed dimensions (person, project, topic, tag, file, symbol, etc.)

• Thought temporality — thoughts have types (fact, decision, observation, question) and can be superseded while preserving history

• Multi-brain support — isolated knowledge spaces via the BRAIN_NAME environment variable

• Conflict detection — automatically surfaces similar existing thoughts when capturing new ones

• Architecture Decision Records — structured ADR capture with auto-numbering, alternatives, and consequences

• Code-linked knowledge — link thoughts to repositories, files, and symbols (brain-code-mcp)

• Knowledge freshness — detect stale knowledge when referenced code changes (brain-code-mcp)

Tools

Core tools (both servers)

Code tools (brain-code-mcp only)

Core prompts (both servers)

Code prompts (brain-code-mcp only)

Setup

Prerequisites

• Node.js

• PostgreSQL with pgvector extension

• An OpenRouter API key (for generating embeddings)

Quick start (Claude Code)

Set OPENROUTER_API_KEY in your shell environment (e.g. in ~/.bashrc or ~/.zshrc):

export OPENROUTER_API_KEY="your-key-here"

Then add to your project's .mcp.json:

{
  "mcpServers": {
    "brain": {
      "command": "npx",
      "args": ["-y", "github:markschaake/brain-mcp"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@host:5432/brain",
        "BRAIN_NAME": "personal"
      }
    }
  }
}

For brain-code-mcp (includes code-aware tools):

{
  "mcpServers": {
    "brain": {
      "command": "npx",
      "args": ["-y", "-p", "github:markschaake/brain-mcp", "brain-code-mcp"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@host:5432/brain",
        "BRAIN_NAME": "my-project"
      }
    }
  }
}

Note: Do not put OPENROUTER_API_KEY in .mcp.json — it is often checked into version control. The server reads it from the environment automatically.

The database schema is automatically created on first run.

Database options

Option 1: Use the included docker-compose (easiest for local development)

git clone https://github.com/markschaake/brain-mcp.git
cd brain-mcp
docker compose up -d   # starts PostgreSQL+pgvector on port 5488

With docker-compose, the default DATABASE_URL (postgresql://brain:brain@localhost:5488/brain) works without any configuration.

Option 2: Bring your own PostgreSQL

Any PostgreSQL instance with the pgvector extension installed will work. Set DATABASE_URL in your MCP config. The schema is auto-applied on first server startup.

Local development

pnpm install
pnpm run build
pnpm run dev    # watch mode (tsc --watch)
pnpm run lint   # run ESLint

# Run directly
OPENROUTER_API_KEY=your-key node dist/index.js      # brain-mcp
OPENROUTER_API_KEY=your-key node dist/code.js        # brain-code-mcp

Environment variables

Multi-brain usage

All tools and prompts accept an optional brain parameter to target a specific brain by name at runtime, without restarting the server. Omit it to use the default brain (BRAIN_NAME).

Read-only tools (search, list_recent, explore_dimension, list_dimensions, list_adrs, search_code, check_freshness, refresh_stale_knowledge) also accept brain: "*" to query across all accessible brains.

Write tools (capture_thought, supersede_thought, capture_adr, capture_code_context) reject "*" — you must specify a brain name for writes.

Use BRAIN_ACCESSIBLE to restrict which brains a server instance can access:

{
  "mcpServers": {
    "brain": {
      "command": "npx",
      "args": ["-y", "github:markschaake/brain-mcp"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@host:5432/brain",
        "BRAIN_NAME": "personal",
        "BRAIN_ACCESSIBLE": "personal,work,shared"
      }
    }
  }
}

When BRAIN_ACCESSIBLE is empty (default), all brains are accessible.

Architecture

Source files

Database schema

Migrations are in migrations/ and are auto-applied on server startup.

• brains — isolated knowledge spaces

• thoughts — content + vector(1536) embedding + metadata (jsonb) + thought type + status

• dimensions — typed categories with metadata, unique per (brain, name, type)

• thought_dimensions — many-to-many links with optional context

Embeddings are indexed with HNSW for fast cosine similarity search.

Code-linked dimension types

brain-code-mcp uses these dimension types to link knowledge to code:

ADR metadata

ADRs are stored as decision thoughts with structured metadata:

{
  "adr": true,
  "adr_number": 7,
  "adr_title": "Use pgvector for semantic search",
  "adr_status": "accepted",  // proposed | accepted | deprecated | superseded
  "adr_context": "Why this decision was needed...",
  "adr_alternatives": [{ "name": "Pinecone", "pros": [...], "cons": [...] }],
  "adr_consequences": ["Must run PostgreSQL with pgvector"],
  "adr_decided_date": "2026-03-01"
}

License

ISC