sherlock-second-brain

Named after the famous detective of Baker Street who inspired this project: the same way, we run rigorous investigations (symptoms, clues, hypotheses, evidence, conclusion) to debug, analyze code, and remember what we learn across multiple projects.

MCP server + skill for Sherlock's second brain: validated knowledge lives in MD fiches and skills; everything not yet validated lives in cases (JSON investigation files for debugging and troubleshooting). Standalone notes worth remembering without an investigation live in memories (MD + YAML frontmatter). A resolved case is promoted into a fiche or a skill through the MCP; a memory can also be promoted into a fiche.

source of truth (files)                      derived index (rebuildable)
────────────────────────────────────             ────────────────────────────
<data_dir>/
  cases/<case-id>/case.json          ──→   vector/ (chromadb, gitignored)
  cases/<case-id>/evidence/*.log           hybrid search: vector (Chroma)
  memories/<id>.md                           + lexical (RRF)
  fiches/*.md
  skills/<slug>/SKILL.md

Stack

• Python 3.12+, uv

• FastMCP (stdio)

• ChromaDB + fastembed (vector index, multilingual MiniLM-L12 model)

• jsonschema (case validation)

• jinja2 (rendering of promoted fiches / skills)

• PyYAML (memory frontmatter)

• Hexagonal architecture: domain/ (pure pydantic) · application/ (use cases + ports) · adapters/ (filesystem, chroma, lexical, hybrid RRF, MCP DTO, templates)

Related MCP server: brain-mcp

Installation (in a project)

uv init
uv add sherlock-second-brain

Or from the repo:

cd sherlock-second-brain
uv sync

Two ways to run it

Your data (cases, fiches, skills, vector index) always lives on the machine where the server process runs. The server is local-first (stdio), so you choose where that machine is:

A. Self-hosted (data stays on your machine)

Install the package and run the stdio server locally — no third party ever touches your data. Configure SHERLOCK_BRAIN_DATA_DIR to choose where the files live (default ~/sherlock-second-brain-data).

B. Managed on Glama (opt-in)

Deploy your own instance on Glama's hosting from the Glama listing: Glama builds the image, wraps the stdio transport into Streamable HTTP, and mounts a persistent volume at /data. Set SHERLOCK_BRAIN_DATA_DIR=/data so your knowledge survives redeploys. This is a paid managed option — the code itself is free and open source (MIT).

Configuration

Wire the MCP server into opencode

Add to ~/.config/opencode/opencode.json:

{
  "mcp": {
    "sherlock-second-brain": {
      "type": "local",
      "command": ["/opt/sherlock-second-brain/.venv/bin/python", "-m", "sherlock_second_brain.server"],
      "enabled": true,
      "environment": {
        "SHERLOCK_BRAIN_DATA_DIR": "/opt/infra/kb"
      }
    }
  }
}

Install the agent globally

The agent is versioned in this repo (agent/sherlock-second-brain.md). To make it available to all opencode agents:

ln -s /opt/sherlock-second-brain/agent/sherlock-second-brain.md ~/.config/opencode/agent/sherlock-second-brain.md

On another machine, clone the repo then create the same symlink pointing to the checkout. Restart opencode after installation.

MCP tools

Cases

Memories

KB

Hybrid search

case_search (and memory_search) combines two engines via Reciprocal Rank Fusion (adapters/hybrid.py) over four sources: fiches, cases, skills and memories.

• Vector (adapters/chroma.py): multilingual embeddings (MiniLM-L12, ~0.22GB, French included), persistent collection in vector/, rebuildable via index_rebuild.

• Lexical (adapters/lexical.py): token overlap, zero dependency — a doc relevant for an exact term but missed by the vector engine still surfaces.

RRF fusion: score(d) = 1/(k + vector_rank) + 1/(k + lexical_rank), k = 60. The first index_rebuild downloads the model.

Memories

A memory is a low-friction capture ("remember that the NAS runs Fedora 44"), with no case workflow. It is stored as memories/<id>.md with YAML frontmatter (metadata) and a free-form markdown body. Memories are indexed on every mutation (create included) so they are immediately searchable. A memory is not validated; promote it with memory_promote once it becomes validated knowledge.

Case schema

Defined in src/sherlock_second_brain/schema/case.schema.json — source of truth, shipped inside the package. Every case written through the MCP is validated against this schema (works from PyPI installs too).

Tests

uv run ruff check src/ tests/        # lint
uv run ty check                      # type checking
uv run pytest tests/ -v              # tests