Tacitus MCP Server

Tacitus

Long-term memory for your AI agents — local-first, with provenance.

Tacitus is an MCP server that turns any folder of Markdown notes into an agent-native knowledge base. It gives AI agents (Claude Code, Claude Desktop, and any MCP client) three things they actually need:

1. Memory with provenance — typed, queryable long-term memory. Every fact carries its source and is returned within a token budget; contradictions are surfaced, not silently resolved.
2. Retrieval that fits the context window — search returns ranked snippets (never whole notes) under a token budget; get_note discloses progressively (outline → frontmatter → full); the wikilink graph is a queryable API. Hybrid lexical + semantic search, with an optional neural embedder.
3. Safe write-back — propose a changeset, preview the diff, commit atomically, and revert by version. Read-only scope forbids mutations; every write is audited.

Notes stay as plain .md files in your folder. No cloud, no lock-in.

Quick start

npx -y @dashiro/tacitus-mcp-server /path/to/your/vault

Claude Code

claude mcp add tacitus -- npx -y @dashiro/tacitus-mcp-server /path/to/your/vault

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "tacitus": {
      "command": "npx",
      "args": ["-y", "@dashiro/tacitus-mcp-server", "/path/to/your/vault"]
    }
  }
}

Tools

Every tool validates input with a schema and returns structured, actionable errors ({ code, reason, suggestion }) rather than stack traces.

Semantic search (optional neural embeddings)

search defaults to hybrid mode (lexical + a deterministic, offline embedder that catches morphological variants). For synonym/paraphrase matching, opt into a neural embedder:

npm i @huggingface/transformers
TACITUS_EMBEDDER=transformers npx @dashiro/tacitus-mcp-server /path/to/vault

Vectors are cached under .tacitus/vectors/. Falls back to the deterministic embedder if the optional dependency or model isn't available.

How it stores things

your-vault/
├── notes...             ← your Markdown files (untouched format)
└── .tacitus/
    ├── memory/*.md      ← agent memories (Markdown + YAML frontmatter)
    ├── vectors/*.json   ← cached embeddings
    ├── history/*.json   ← version snapshots (for revert)
    └── audit.log        ← JSONL log of every agent write

Development

Polyglot monorepo. The reference server (shipped on npm) is TypeScript in packages/mcp-server. A native Rust server in crates/ is being ported for a single-binary, zero-runtime-deps build (crates/tacitus-core engine + crates/tacitus-mcp rmcp server). Its stable_id matches the TS engine byte-for-byte, so memory ids are identical across both engines.

# TypeScript server
npm ci
npm test          # vitest
npm run typecheck
npm run lint
npm run build     # tsup → packages/mcp-server/dist
npm run eval      # retrieval quality report

# Rust server (native, single binary)
cargo test
cargo clippy --all-targets -- -D warnings
cargo fmt --check
cargo run -p tacitus-mcp -- /path/to/vault   # runs the memory MCP server on stdio
cargo build --release                         # → target/release/tacitus-mcp

The Rust server currently exposes the memory tools (remember, recall, forget); retrieval and write-back tools are being ported next.

License

MIT — see LICENSE.