thebrain

thebrain-mcp

An MCP server for TheBrain 15, built on its local API.

It gives an agent semantic operations over your brain: search by meaning, read a neighbourhood of the graph, and write a decomposed piece of material into the brain as a whole connected structure. It is not a mirror of the API — 19 tools instead of 48 endpoints.

The point is not "save this text". The point is that when you hand an agent an article, it reads it, breaks it into meanings, works out where each one belongs in the graph you already have, what to link it to, and what each note should say.

Published on npm as thebrain-mcp-server — npm considers the shorter name too close to an unrelated existing package. The installed command is still thebrain-mcp.

Requirements

• TheBrain 15 running, with the local API enabled
• Node.js 22 or newer
• An API key: Settings → User → Local API Key

Install

Claude Code

claude mcp add thebrain -e THEBRAIN_API_KEY=your-key -- npx -y thebrain-mcp-server

Clients with a config file

{
  "mcpServers": {
    "thebrain": {
      "command": "npx",
      "args": ["-y", "thebrain-mcp-server"],
      "env": { "THEBRAIN_API_KEY": "your-key" }
    }
  }
}

Semantic search

TheBrain's own search matches prefixes: OT finds OTGP, while a synonym or a typo finds nothing. To search by meaning, the server builds a local vector index.

The embeddings package is not part of the install: it weighs around 380 MB, plus 113 MB for the model itself on first run. Install it separately, and only if you want it:

npm install -g @huggingface/transformers

Then, from your client: brain_index with action: "rebuild". Indexing a 10,000-thought brain takes about a minute; later runs only recompute what changed.

The server works without the package. brain_search falls back to a fan-out of prefix queries over the synonyms the agent supplies, and says plainly that recall is lower.

Everything is local: neither your brain's contents nor your queries are sent anywhere.

Settings

Variable	Default	Purpose
THEBRAIN_API_KEY	—	Required
THEBRAIN_BASE_URL	http://localhost:11522, then :8001	Local API address
THEBRAIN_DATA_DIR	~/.thebrain-mcp	Where indexes are stored
THEBRAIN_ALLOW_DESTRUCTIVE	0	Allow deleting thoughts and links
THEBRAIN_EMBEDDING_MODEL	Xenova/multilingual-e5-small	Embedding model
THEBRAIN_EMBEDDING_DTYPE	q8	Weight precision
THEBRAIN_TIMEOUT_MS	30000	API request timeout

Changing the model or the precision makes an existing index unusable — the server will say so and ask for a rebuild.

THEBRAIN_BASE_URL rarely needs setting. A TheBrain update moved the local API from port 8001 to 11522, so the server tries the new port and falls back to the old one. Set the variable only if TheBrain listens somewhere else; the endpoint exactly as Settings shows it (http://localhost:11522/api/) is fine.

Tools

Reading

Tool	What it does
brain_list	Brains, which one is open, whether the index is ready
brain_get_thought	A thought, its aliases, its graph and its note in one call
brain_search	Search by meaning
brain_traverse	Walk the graph several hops out
brain_list_types_and_tags	The brain's vocabulary
brain_recent_changes	What changed, in plain language
brain_index	Index status, build and refresh

Writing

Tool	What it does
brain_create_thought	A thought together with its note, type, tags and aliases
brain_update_thought	Name, label, type, colours; add and remove aliases
brain_set_note / brain_append_note	Replace or extend a note
brain_link	Connect two thoughts, with a label; with replace, make the link that joins them another kind
brain_unlink	Remove a link, with human confirmation
brain_tag	Attach and detach tags
brain_create_type_or_tag	A new type or tag; a tag of a name the brain has is given back, not made twice
brain_attach_url	Attach a link, without duplicates
brain_activate	Open a thought on the user's screen
brain_delete_thought	Delete, with human confirmation
brain_ingest	Write a whole structure in one call

brain_ingest

The main tool for filling a brain. The agent breaks material into thoughts, wires them together through temporary identifiers, and the whole thing lands in one call:

{
  "brainId": "…",
  "thoughts": [
    { "tempId": "art",   "name": "Article on RAG", "parent": "<uuid of an existing thought>" },
    { "tempId": "embed", "name": "Embeddings", "parent": "art", "note": "…" },
    { "tempId": "store", "name": "Vector store", "parent": "art" }
  ],
  "links": [
    { "from": "embed", "to": "store", "name": "is written into" }
  ]
}

The order of thoughts in the input does not matter — dependencies resolve themselves. Running the same plan twice duplicates nothing, and a thought that was already there keeps the note it has: a plan's note is written only where there is none, and the result says which notes were kept. Bad plans (a cycle, a reference to nowhere) are rejected before the first write.

Skills

The server provides the mechanism — deterministic operations. The methodology (how finely to split meanings, when to attach to something that already exists, what belongs in a note) lives separately, in Claude Code skills. They are plain markdown files, so you can adjust them to your own way of working without rebuilding the server.

Skill	When it fires
thebrain-ingest	"put this article in my brain", "break this down and record it"
thebrain-research	"what do I know about X", "have we discussed this already?"
thebrain-organize	"clean up my brain", "find duplicates"
thebrain-digest	"what did I add this week", "what have I been working on"

Install them as symlinks, so edits in the repository take effect immediately:

mkdir -p ~/.claude/skills
for d in skills/*/; do
  ln -sfn "$PWD/$d" ~/.claude/skills/"$(basename "$d")"
done

Or copy them, if you do not want the link to the repository. For a single project, use .claude/skills in its root instead of ~/.claude/skills.

Skills are picked up when a session starts — an already running session needs a restart (claude --continue keeps the conversation).

Deletion

Of a thought (brain_delete_thought) and of a link (brain_unlink). Off by default. Even with THEBRAIN_ALLOW_DESTRUCTIVE=1 it requires human consent: through a confirmation form if the client supports one, otherwise through a second call with an explicit flag. The agent cannot make this decision for you.

Development

npm install
npm test                 # unit tests, no live TheBrain needed
npm run build

Contract tests against a live API:

THEBRAIN_API_KEY=… npm test                                  # read-only
THEBRAIN_API_KEY=… THEBRAIN_TEST_BRAIN_ID=<uuid> npm test    # + writes

The write tests require a separate, throwaway brain and refuse to touch any brain with more than 500 thoughts. The read-only tests that need a brain read that one too, and skip without it: no test reads another brain.

Documentation

• ARCHITECTURE.md — how the server is built and why: layer boundaries, the mechanism/policy split, error philosophy, the semantic layer, and the reasons behind each decision.
• docs/api-map.md — the local API's behaviour, including the undocumented parts, verified against a live instance, with the measurements.
• docs/stack-evaluation.md — why TypeScript, with numbers.
• CONTRIBUTING.md — how to work on this.

Support

thebrain-mcp is built and maintained in spare time. If it earns a place in your workflow, you can sponsor it on GitHub — once or monthly.

License

MIT