Thoth-Mem

Persistent memory for AI coding agents

Give coding agents durable project memory across sessions, compactions, and context resets.

Thoth-Mem is a local-first MCP server backed by SQLite and FTS5. It preserves useful decisions, bug fixes, conventions, and session continuity, then retrieves only the evidence an agent needs. The same installation also provides a CLI, an optional HTTP API, and native lifecycle integrations for supported coding harnesses.

Global scope manages the current user's harness configuration; project scope is explicit and confined to the selected project and its receipt tree. Engram, thoth-agents, or another memory integration may overlap; treat this as a warning only: thoth-mem does not edit, disable, remove, or write to external repositories.

First use

Requires Node.js 18 or newer.

npx -y thoth-mem@latest mcp

This starts the MCP server and its local HTTP bridge. For a persistent command that native integrations can invoke, install the CLI globally:

pnpm add -g thoth-mem
thoth-mem mcp

New client configurations should use the explicit mcp subcommand. Add --no-http when only the MCP transport is wanted.

Related MCP server: LumenCore

The memory loop

A useful agent workflow is small and repeatable:

1. Save the durable lesson. Use mem_save for a decision, root cause, convention, or other non-obvious fact that should survive the current context.

2. Recall narrowly. Start with mem_recall(mode="compact"), expand strong candidates with mode="context", and fetch a complete selected record with mem_get.

3. Resume with identity. Keep the same stable session_id and project; use mem_context for recent continuity and mem_session for root-owned lifecycle events.

Example observation:

{
  "kind": "observation",
  "title": "Retry SQLite writes in a new transaction",
  "type": "bugfix",
  "project": "my-project",
  "topic_key": "sqlite/busy-retry",
  "content": "**What**: Roll back after SQLITE_BUSY and retry in a new transaction.\n**Why**: Retrying inside the failed transaction repeats the failure.\n**Where**: write transaction helper.\n**Learned**: Use bounded backoff before opening the new transaction."
}

Remove content inside <private>...</private> before persistence. Do not store credentials, complete transcripts, generated agent prompts as user intent, or raw logs without a reusable lesson.

Six MCP tools

Setup, sync, migration, rebuild, and maintenance commands are CLI/HTTP administration, not additional MCP tools.

Inspect graph communities

Communities are bounded summaries derived from a project's knowledge graph. An operator builds or refreshes the committed summaries through the CLI:

thoth-mem rebuild-communities --project my-project

An agent then obtains them through mem_project:

{
  "action": "graph",
  "project": "my-project",
  "navigation": "community",
  "limit": 5,
  "max_chars": 2000
}

The response reports community state and freshness, then entries such as community=<id>, graph coverage, confidence, degradation state, a bounded summary, and sources=obs:<id>. Community inspection requires a project but no focus node or observation ID. If no committed summaries exist, it says so instead of synthesizing a global answer.

To inspect evidence behind a community, take an obs:<id> from its sources field and call mem_get(kind="observation", id=<id>). Observation IDs also appear in recall results. For a bounded graph neighborhood, reuse one as focus_node_id="obs:<id>" with navigation="neighborhood".

Native harness integrations

Native setup installs the packaged MCP declaration, memory skill, and lifecycle hooks where the harness supports them. Inspect the zero-write plan first, then rerun without --plan to apply it:

The default OpenCode setup command is thoth-mem setup opencode; add thoth-mem setup opencode --scope project --project /path/to/project --force when explicitly targeting a project, or use thoth-mem setup codex --rollback /path/to/receipt.json for a receipt-scoped rollback.

Setup status and process exit codes are stable:

Project-local setup is explicit:

thoth-mem setup opencode --scope project --project /path/to/project --plan --json

Review detected conflicts before applying. Use --force only for conflicting locations whose thoth-mem ownership is already proven; it does not grant authority over unrelated configuration.

Claude Code also supports its native marketplace flow:

claude plugin marketplace add EremesNG/thoth-mem
claude plugin install thoth-mem

Native integration is optional. Existing memories and the six-tool MCP server continue to work with a manual connection.

Manual MCP fallback

Native hooks are optional. Keep a plain six-tool MCP connection when you do not want managed setup or a native plugin; existing memories remain available.

Transitioning to native harness integration

Native setup is opt-in: inspect the zero-write plan, review conflicts, then apply the matching harness command. For Codex, open /plugins, install thoth-mem from EremesNG/thoth-mem, and verify the marketplace and plugin state. External Codex registration is not atomically reversible, so confirm external state before retrying or rolling back local setup.

Managed setup contract: Plan mode performs zero writes and only mutation at thoth-mem-managed locations. Backups are created before the first mutation; OpenCode accepts opencode.json or opencode.jsonc. Each mutating attempt writes an HMAC-protected receipt with status in_progress before changes:

• global receipts: <thoth-data-dir>/setup/receipts/<receipt-id>/receipt.json

• project receipts: <project>/.thoth/setup/receipts/<receipt-id>/receipt.json

Missing or tampered receipts fail closed. A verified rollback preserves unrelated settings, while drift or unavailable capabilities return requires_user_action. Repeated setup and repeated completed rollback are no-ops when verified state already matches.

Gemini CLI: manual MCP

Gemini CLI is a manual MCP client path, not a managed native thoth-mem integration. Add this entry to ~/.gemini/settings.json:

{
  "mcpServers": {
    "thoth": {
      "command": "npx",
      "args": ["-y", "thoth-mem@latest", "mcp"]
    }
  }
}

Evaluate retrieval and graph quality

The repository includes deterministic evaluation commands:

pnpm run eval:retrieval
pnpm run eval:kg

eval:retrieval seeds signal observations plus distractors and measures whether the expected memory ranks near the top. Read its report as a collection of signals:

• Recall and rank show whether the right evidence was found and how early.

• Noise and case mix show robustness across direct, rephrased, and repository-derived examples.

• Compression shows how much evidence was removed before context delivery; it is an efficiency signal, not proof that the remaining text is correct.

• Lane and fallback evidence shows lexical, semantic raw/HyDE, and KG participation, including pending or degraded semantic behavior.

• Lineage and provenance show whether returned evidence remains attributable to its source.

eval:kg measures expected subject-relation-object recall, forbidden-triple leakage, deterministic extraction behavior, and validated optional LLM enrichment. Missing expected facts indicate coverage gaps; forbidden hits indicate unsafe graph invention.

These evals are deterministic development gates over curated and synthetic fixtures. They do not predict every production corpus, replace human review, prove a native harness integration, or by themselves justify enabling optional community read paths. Compare the individual cases and failure messages instead of treating one aggregate number as universal quality.

Scale retrieval noise when you want a tougher local run:

$env:THOTH_RETRIEVAL_EVAL_NOISE='250'
pnpm run eval:retrieval

Advanced operations

• Run thoth-mem help for the complete CLI command and option list.

• Open the local dashboard at http://localhost:7438/ and OpenAPI documentation at http://localhost:7438/docs.

• Use thoth-mem sync --dir=.thoth-sync and thoth-mem sync-import --dir=.thoth-sync for Git-friendly portability.

• Review config.schema.json for persisted configuration and environment-backed settings.

• Data lives in ~/.thoth/thoth.db by default; override the data directory with THOTH_DATA_DIR or --data-dir.

Semantic indexing is non-blocking. If embeddings or sqlite-vec are unavailable, recall remains usable through supported lexical and graph evidence and reports the degraded lane instead of silently claiming semantic success.

Development

pnpm install
pnpm run integration:verify
pnpm run build
pnpm test

License

MIT