second-brain-mcp

An MCP server that exposes an Obsidian vault to Claude — read, search, and write notes, capture voice thoughts into the right folder with the right frontmatter, and manage Tasks.md.

Built so the vault's filing rules live in code rather than in a prompt that can be forgotten.

Status

Related MCP server: Vault MCP Server

Quick start

Requires uv. Python comes from uv; the system python3 is too old.

uv sync

# Point at a COPY of your vault first. Never the real one until you trust it.
rsync -a ~/Library/CloudStorage/SynologyDrive-Mergoth/Notes/PersonalObsidian/ /tmp/vault-copy/

VAULT_PATH=/tmp/vault-copy uv run python -m second_brain_mcp

That starts the stdio server. It will refuse to start without VAULT_PATH — there is no default, deliberately, because a default is how a test run reaches the real vault.

Connect it to Claude Desktop

{
  "mcpServers": {
    "second-brain": {
      "command": "uv",
      "args": ["run", "--directory", "/Users/vladislav/work/second-brain-mcp",
               "python", "-m", "second_brain_mcp"],
      "env": { "VAULT_PATH": "/Users/vladislav/work/vault-sandbox/PersonalObsidian" }
    }
  }
}

HTTP transport

VAULT_PATH=/tmp/vault-copy MCP_AUTH_TOKEN=$(openssl rand -hex 32) \
  uv run python -m second_brain_mcp --transport http

Serves on 127.0.0.1:8000, MCP endpoint at /mcp. Every request needs Authorization: Bearer <token>; unauthenticated requests get a 401 with a WWW-Authenticate header pointing at /.well-known/oauth-protected-resource (RFC 9728).

Configuration

All configuration is environment variables. None have defaults.

Tools

Primitives — no vault knowledge

Semantic — encodes the vault's rules

add_task requires an explicit section and raises listing the available ones if it doesn't match. It does not guess and has no default section. This is deliberate: the vault's own CLAUDE.md says "Sections are a view, not a taxonomy. Re-sort when reality moves", so any hardcoded section table would silently misfile tasks the next time you reorganise. Call list_task_sections() first.

add_task never invents a date or priority, and reports back any marker it added that you did not state.

capture_thought rejects a domain outside the closed list (work finance legal health trips home plants smart-home projects learning) rather than inventing one.

Security model

The server is a plain local-filesystem server. Its one real control is path confinement.

• Every caller-supplied path becomes a real path in exactly one function, vault/paths.py::resolve(). Nothing else in the package opens a file by a caller-supplied path.

• The vault root is resolved once at startup and frozen. It is not a tool argument and cannot be changed at runtime.

• resolve() takes one parameter. There is no bypass flag, no per-call root, no trusted-path list, no follow-symlinks toggle.

• Containment is checked by path ancestry, never string prefix — with root /vault, the sibling /vault-evil must not pass.

• Rejected: .., absolute paths, null bytes, empty paths, and symlinks that resolve outside the root even when the link itself lives inside the vault.

• Glob patterns and search scopes are validated too, and the search query goes to rg after -e so it can never be parsed as a flag.

That last point is not theoretical. An early build appended the caller's query to rg as a bare positional argument, so a query of --pre=<script> executed arbitrary commands — with a model-controlled argument, which is exactly the prompt-injection threat the design exists to stop. See factory/adr/0002-single-path-resolution-chokepoint.md.

No hard delete anywhere. Archiving is move_note into raw/archive/.

Every mutation appends a line to meta/audit.log (machine-readable, append-only). That is deliberately a different file from meta/log.md, which stays human-curated so an unexplained line in it is still a usable tripwire.

Development

uv run --frozen pytest -q     # 119 tests
uv run ruff check .

Tests run against a synthetic fixture vault copied into tmp_path. An autouse guard fails the session if the resolved vault root is not under tmp_path, so the suite cannot reach a real vault.

Design documents:

• factory/briefs/vault-mcp-server.md — why it is built this way, and what was rejected

• factory/adr/ — binding architecture decisions

• specs/ — what each increment builds

• docs/initial_spec.md — the original design record

Deployment

Phase 3 is not done. What remains is NAS and browser work, not code:

1. Fix the advertised metadata URLs first — this is a blocker, not a nicety. __main__.py calls build_auth_settings() with no arguments, so it advertises the defaults resource_url="http://127.0.0.1:8000" and issuer_url="https://auth.example.com". Behind a reverse proxy those are wrong: a remote client is told the resource lives on loopback. Make both read from the environment (e.g. MCP_RESOURCE_URL, MCP_ISSUER_URL) before exposing anything.

2. Build the container. deploy/Dockerfile and deploy/compose.yaml are written — non-root user, read-only rootfs, ripgrep installed, port bound to 127.0.0.1 — but have never been built or run.

3. Resolve container UID vs. vault file ownership. Tasks.md and meta/log.md are mode 600 on the real vault, so a non-root container with a mismatched UID gets EACCES on exactly the two highest-value writes while reads of raw/ keep working — a partial failure that looks like a tool bug.

4. DSM reverse proxy, Let's Encrypt cert, rate limit, auto-block on failed auth. Never publish the container port directly.

5. Register as a custom connector and test from Android.

On auth

docs/initial_spec.md assumed custom connectors require OAuth 2.1 with dynamic client registration. That is out of date: DCR is deprecated in the current MCP spec (Client ID Metadata Documents replace it), and static bearer tokens are first-class on Anthropic's MCP client surfaces. So this ships a static bearer.

The honest caveat: that is evidence about Anthropic's API surfaces. Whether the claude.ai custom connector UI accepts a static bearer is a product question that needs a live test. If it turns out to demand OAuth, auth.py is the only module that changes — transport and auth are confined to the entrypoint by factory/adr/0003.

Known limitations

• The container image is unbuilt and unverified.

• RFC 9728 metadata URLs are hardcoded defaults (see Deployment step 1).

• list_notes(since) filters on filesystem mtime, which on a Synology-synced folder is sync time, not edit time. The vault's CLAUDE.md says created: in frontmatter is the real recency anchor.

• No end-to-end test drives a JSON-RPC tool call over HTTP; tools are covered over stdio and via direct calls.

• propose_wiki_page from the original spec is deliberately not built — its arguments were never specified and it serves deep work at the desk, where nothing is blocked.

• Synology sync conflicts are not handled. Writes are atomic (temp file + os.replace), but there is no merge logic. The original spec cited conflict files as evidence this was urgent; there are none in PersonalObsidian/, so the risk is real but unproven and was not paid for.