Fortytwo Guide

A standalone semantic-memory MCP server. It stores text "memories" with free-form provenance and recalls them by meaning (vector search), by keyword (FTS5), or by structured filter. Backed by SQLite + sqlite-vec, embeddings from a local Ollama model.

It is persona-agnostic: no journal/persona/approval coupling, just a generic memory store and tool surface. It can be used on its own, or as a Claude Code plugin.

What it stores

A memory is content plus provenance:

field	meaning
content	the text (embedded for recall)
source	where it came from — free-form (owner, web, tool:foo)
observed	how it was observed — free-form (stated, inferred, imported)
date	ISO date the memory pertains to (defaults to today, UTC)
tags	free-form tags for filtering
supersedes	id of a prior memory this one replaces (history is kept)

Recall is hybrid: recall (semantic), lexical (FTS5 keyword), and query (structured). reindex + recall_docs index/search a directory of markdown documents separately from the memory store.

MCP tools

The server registers under the id fortytwo-memory, so a consumer calls the tools as mcp__fortytwo-memory__<tool>:

tool	description
store	store a memory (+ provenance); set supersedes to replace one
query	structured query (source/observed/tag/time; live rows by default)
recall	semantic top-k recall by meaning
recall_docs	semantic recall over reindexed markdown
lexical	full-text keyword search (FTS5)
reindex	self-heal the doc index from a markdown directory
export_range	render a date range of memories to markdown

Contract version

Consumers depend on the tool surface, not the internals. The contract is versioned:

import { MEMORY_TOOL_CONTRACT_VERSION, memoryToolContract } from '@justfortytwo/memory/contract';

• A major change to a tool name, its required inputs, or its result shape is a contract break → bump MEMORY_TOOL_CONTRACT_VERSION. Siblings pin a caret range on @justfortytwo/memory, so a major bump forces an explicit opt-in.
• Additive changes (new optional inputs, new tools) do not bump it.

memoryToolContract is the authoritative human-readable list of tools and their guarantees, kept in sync with the wire schema in src/tools.ts.

Embedder

The default embedder is OllamaEmbedder, which calls a local Ollama /api/embeddings endpoint.

OLLAMA_BASE_URL=http://localhost:11434   # default
EMBED_MODEL=qwen3-embedding:0.6b         # default model (1024-dim)

Pull the model once:

ollama pull qwen3-embedding:0.6b

If EMBED_MODEL is unset, the server falls back to a deterministic, dependency-free FakeEmbedder — useful for tests, CI, and first-run smoke checks with zero infra. (The vector tables are fixed at 1024-dim; a model with a different dimensionality requires a schema change.)

Standalone usage

npm install @justfortytwo/memory

Prerequisites. Requires Node.js >= 20. The package depends on better-sqlite3 ^12, a native module that ships prebuilt binaries for LTS Node releases — on an unsupported Node version or platform, npm install will compile it from source (needs a C/C++ toolchain). It also needs a local (or remote) Ollama for real embeddings; without EMBED_MODEL set it falls back to a deterministic FakeEmbedder (see Embedder). sqlite-vec ships as a bundled npm dependency — no manual SQLite-extension install is needed.

# build (once); the server runs the built JS, not TS
npm run build

# apply migrations to the DB (DB_PATH or ./memory.db)
DB_PATH=./memory.db npm run migrate

# run the MCP server over stdio
DB_PATH=./memory.db EMBED_MODEL=qwen3-embedding:0.6b fortytwo-memory

The bin is fortytwo-memory → dist/index.js. You can also run it with npx -y @justfortytwo/memory (it is published to npm).

Register in your own .mcp.json

To use the server in any MCP host (not as a Claude Code plugin), drop this into your project's .mcp.json with a real DB path:

{
  "mcpServers": {
    "fortytwo-memory": {
      "command": "npx",
      "args": ["-y", "@justfortytwo/memory"],
      "env": {
        "DB_PATH": "./memory.db",
        "EMBED_MODEL": "qwen3-embedding:0.6b",
        "OLLAMA_BASE_URL": "http://localhost:11434"
      }
    }
  }
}

OLLAMA_BASE_URL may point at a remote host. The embedder strips a trailing slash, so either form works — but prefer no trailing slash.

As a library

import { openDb, runMigrations, OllamaEmbedder, store, recall, deleteByIds } from '@justfortytwo/memory';

const h = openDb('memory.db');
await runMigrations(h.k);
const embedder = new OllamaEmbedder();

await store(h, embedder, { content: 'the deploy script lives in scripts/deploy.sh', source: 'owner', observed: 'stated' });
const hits = await recall(h, embedder, 'how do I deploy?', 5);

deleteByIds(h, [hits[0].id]); // hard-delete (row + vector + FTS); returns the count removed

Deleting memories

deleteByIds(h, ids) hard-deletes memories — the row, its vector, and its FTS entry — so nothing resurfaces in recall/lexical/query. It is intentionally a library API and NOT an MCP tool: deletion is an owner-privileged operation, and exposing it to the assistant's turn loop would let prompt-injected content trick it into erasing memories. Selecting which ids to remove (by query, tag, date range, …) is the caller's job — see @justfortytwo/installer's forget.

As a Claude Code plugin

.claude-plugin/plugin.json declares the plugin; .mcp.json registers the fortytwo-memory server. By default it launches via npx:

{
  "mcpServers": {
    "fortytwo-memory": {
      "command": "npx",
      "args": ["-y", "@justfortytwo/memory"],
      "env": {
        "OLLAMA_BASE_URL": "http://localhost:11434",
        "EMBED_MODEL": "qwen3-embedding:0.6b",
        "DB_PATH": "${CLAUDE_PLUGIN_DATA}/memory.db"
      }
    }
  }
}

${CLAUDE_PLUGIN_DATA} survives plugin updates, so the DB persists across upgrades. When developing from source, build first (npm run build) and swap the command to node with args ["${CLAUDE_PLUGIN_ROOT}/dist/index.js"]. Claude Code does not build MCP servers — they run via npm/npx.

Continuous enrichment

enrich(h, embedder, candidates) folds a batch of candidate memories into the store: it drops low-salience candidates, dedupes near-duplicates by meaning, and writes the survivors with provenance — honoring an explicit supersedes to replace a stale belief (history is kept, never a silent overwrite). enrichFromTurn(h, embedder, turn, extractor) runs an injected SalienceExtractor and feeds its candidates to enrich.

The salience extractor itself is model-driven and lives in the sibling @justfortytwo/salience engine (a SalienceExtractor with an injected LlmClient) — memory owns only the dedupe + write, never the model call.

Peer seams

memory depends on two sibling packages one-directionally (declared as optional peers, no cycle):

• @justfortytwo/gate — memory ships GateApprovalStore (src/gate-approval-store.ts), a durable SQLite-backed implementation of gate's ApprovalStore + AuditLogger interfaces. Pass it to gate's decide(..., { store, audit }) to back the safety gate's one-shot approvals with memory's db instead of the gate's standalone JSONL store.
• @justfortytwo/salience — the model-driven salience extractor injected into enrichFromTurn (see above).

Development

npm run build      # tsc
npm test           # vitest run
npm run test:watch # vitest

Set RUN_OLLAMA_TESTS=1 to run the opt-in live-Ollama embedder test.

License

MIT © 2026 Enrico Deleo

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Created and maintained by Enrico Deleo.