second-brain-mcp

Turn your Obsidian vault into semantic memory for any MCP-capable coding agent.

v1.0.0 — early release. Works end-to-end on macOS and Linux; published on PyPI on 2026-04-15. Windows is untested. Feedback, bug reports, and testing notes are very welcome — please open an issue if anything misbehaves or if the docs are unclear.

What it does. Ships a stdio MCP server with four read-only tools (obsidian_overview, obsidian_search, obsidian_read, obsidian_backlinks) plus one prompt (to_obsidian) that drives a human-in-the-loop write workflow. Works with Claude Code, Cursor, Zed, or any client that speaks MCP.

What it is not. No auto-writes — nothing is written to the vault without an explicit /to_obsidian invocation. No background extraction, no reflection or compaction loops running on your behalf. The LLM does the extraction work when you call /to_obsidian, but every candidate note requires your explicit per-note approval before it is written. You control what enters the vault; the server only reads from it.

How this is different from other Obsidian MCP servers. Existing Obsidian MCP servers (e.g. variants of mcp-obsidian) typically talk to the running Obsidian app through its Local-REST plugin and expose file-level tools — list_files, get_file, append_to_note, etc. second-brain-mcp is offline and plugin-free: it reads the vault as plain files from disk, builds a local semantic index with bge-m3, and exposes semantic search rather than path-based CRUD. Obsidian does not need to be running. The write path is a curated workflow with per-note human approval, not a raw write_file tool.

30-second quick start

# 1. Install (uvx — no venv pollution)
uvx second-brain-mcp serve --help

# 2. Point at your vault
export OBSIDIAN_VAULT=$HOME/obsidian/vault

# 3. Register with Claude Code
claude mcp add -s user second-brain \
  -e OBSIDIAN_VAULT="$OBSIDIAN_VAULT" \
  -- uvx second-brain-mcp serve

# 4. Restart Claude Code, then ask: "call obsidian_overview"

First run downloads the bge-m3 embedder (~2.3 GB) on the first tool call — roughly 5 seconds after that. See docs/CUSTOMIZE.md for lighter models, or to point at an OpenAI-compatible embeddings API (Cloud.ru FM API, OpenAI, self-hosted Infinity) instead of the local model.

Related MCP server: Nexus MCP for Obsidian

Vault requirements

Hard minimum: a directory with .md files somewhere (any nesting).

Everything else is optional:

• YAML frontmatter (type, verified, confidence) enables filtering

• [[wikilinks]] enable backlinks navigation

• _index.md at the vault root is returned whole in obsidian_overview

Start with your existing vault — unused features simply stay inactive until you add the relevant structure.

Why editorial, not archival

Most agent-memory systems default to the archival model: capture everything — raw conversation turns, every tool call, every message — then rely on semantic search to pull the right thing back later. Comparative retrieval tests against one such system (MemPalace, with its exchange-pair chunking and multi-layer palace) surfaced a clear trade-off: on realistic queries a small set of human-approved notes outperformed a much larger raw conversation archive sitting in the same index.

The reason is simple. In any given session roughly 95% of what's said is working noise — code, syntactic back-and-forth, tactical detail that expires with the task. The 5% that survives — atomic facts, decisions, insights — is what you actually want to find six months later. Archival memory keeps both and leans on the embedder to separate them, and that separation is hard to get right in practice.

second-brain-mcp takes the editorial position: memory is what you chose to remember. Nothing reaches the vault by accident. The loop:

1. You work a session normally. The agent reads from the vault through the four read-only tools but writes nothing on its own.

2. When you're done, you invoke to_obsidian. The agent walks the session, pulls out candidate facts, frames each as an atomic statement, and checks for duplicates against the existing vault.

3. It shows you the list. You approve, reject, merge, or rewrite each candidate individually.

4. Only the approved notes land in the vault.

The LLM does the extraction work — it is good at abstracting and generalising. You are the editor — you know which of the candidates actually matter. The vault ends up small, dense, and almost entirely signal. That curated remnant is what makes retrieval surface the right thing instead of the loudest thing.

This is why there is no reflection loop, no background extraction, no auto-writes. The approval gate is the whole point.

Documentation

• docs/INSTALL.md — per-client setup (Claude Code, Cursor, Zed, generic)

• docs/ARCHITECTURE.md — components, data flow, principles

• docs/WRITE-WORKFLOW.md — to_obsidian explained

• docs/SECURITY.md — read-only guarantees, path-traversal

• docs/CUSTOMIZE.md — alternative embedders, env vars

• docs/TROUBLESHOOT.md — common errors and fixes

• ROADMAP.md — v1.1+ planned features

License

MIT. See LICENSE.

Credits

The pattern of embedding a PROTOCOL string in the first read-tool's response is borrowed from MemPalace's tool_status. The design was shaped by empirical comparisons with raw conversation archives — curation beats volume.