MemAI

A long-term memory MCP server for AI agents. Agents call its tools to write memories (facts, decisions, checkpoints, pitfalls) during a session and read them back in future sessions — the thing that lets an agent "remember" across process restarts, since an MCP server's own process does not persist state between conversations on its own.

Why this exists

Vector-database-backed memory stores usually couple two things that don't like being coupled: an ANN vector index (e.g. HNSW) and a separate metadata store, each with its own durability model. An agent host that manages MCP servers as subprocesses typically kills them abruptly at session end, not cleanly — and a kill that lands between the metadata write and the index flush desyncs the two. The failure mode is silent: search still returns results, just increasingly wrong ones (stale, or referencing entries that no longer exist). This isn't hypothetical — e.g. Chroma 0.5.7–0.5.12 lost not-yet-synced embeddings while keeping their documents (chroma#2922).

MemAI avoids the failure class differently: vectors live inside the same transactional store as everything else. There is no second store with its own durability model, so there is nothing to desync from.

Related MCP server: tartarus-mcp

How it works

Storage. A single SQLite file, WAL mode, holding six things together in one transactional unit:

• memories — the rows themselves (type, domain, session, tags, content, status, confidence, timestamps).

• memories_fts — an FTS5 (BM25, porter-stemmed) full-text index over content + tags + domain, kept in sync with memories via triggers on every insert/update/delete.

• memories_vec — a sqlite-vec vec0 table holding one embedding per memory (over the same content + tags + domain text FTS indexes). sqlite-vec hooks SQLite's transaction lifecycle, so vector writes commit/roll back with the row they belong to.

• edits — full edit history; correcting a memory keeps the previous version instead of overwriting it.

• relations — a queryable graph of typed edges between memories (supersedes, relates_to, contradicts, ...).

• meta — which embedding model (and dimension) produced the stored vectors.

Because everything lives in one file under one set of ACID transactions, there's nothing that can desync from anything else, including across a hard kill — SQLite's WAL journal guarantees the file is either fully committed or rolled back, never half-written. That includes the vectors: no ANN index sitting beside the database waiting for a clean shutdown.

Embeddings. A local model2vec static model (minishlab/potion-base-8M, ~30MB, numpy-only CPU inference) ships bundled inside the package — no Hugging Face download and no network access required, which matters on corporate networks that block huggingface.co. Set MEMAI_EMBED_MODEL to a Hugging Face repo id or a local path to use a different model instead. Embedding versioning is handled explicitly: the meta table records the model name + dimension, and if either changes, all vectors are dropped and re-embedded in one transaction on the next connect — vectors from one model are meaningless in another model's space. If the model can't load (e.g. first run offline), writes proceed without vectors and retrieval degrades to keyword-only (relevant only if MEMAI_EMBED_MODEL points somewhere unreachable); missing vectors are backfilled automatically on a later connect.

Retrieval. search is hybrid: FTS5 BM25 across content/tags/domain, plus brute-force KNN (cosine, no ANN index — nothing to desync, and at memory-store scale linear scan is plenty) over the vectors, merged by reciprocal rank fusion. Each result says which side matched (match_source: fts | vec | both) and carries the raw scores (fts_rank, vec_distance). Both retrievers only widen the candidate set — semantic judgment (does this candidate actually answer the query) is still left to the calling agent: it reads back the candidates and decides relevance itself, the same way it would judge any other tool's output. Multi-term queries are OR'd together on the keyword side, so several paraphrases in one call still help. list_by_domain / list_recent exist as a brute-force fallback for when a search comes back thin.

Recency vs. similarity. pulse and the list_* tools always sort by created_at DESC — never by similarity. Similarity ranking exists only inside search, where it orders candidates for the agent to judge, not answers. A similarity-ranked top-1 can surface an old memory that happens to score well over a same-day one that's actually current, which is exactly why the "what's the latest state" tools stay recency-only.

Confirmation-gated deletion. forget is a soft delete: content is kept, the row is just excluded from default search/list output (status: archived). purge_memory is a real, permanent delete of the row plus its edit history and relations — gated on a confirm_phrase argument that must exactly equal "DELETE <uid>". The intent is that this string can only plausibly come from a human explicitly confirming that exact id in their own words, not from an agent inferring "the user probably wants this deleted."

Tools

An agent can discover all of this at runtime: help() returns every tool with a one-line summary, and help(command='<name>') returns that tool's full signature and docstring, read live from the code.

Writer tool names match the type they store (note() → type='note', reasoning() → type='reasoning', ...), so the verb an agent calls is exactly the string it later filters on.

Setup

python -m venv .venv
.venv/Scripts/pip install -e ".[dev]"   # or .venv/bin/pip on non-Windows
pytest

On Windows, install.bat does the venv + install steps and run-admin.bat starts the admin dashboard (both activate .venv themselves; extra arguments are passed through, e.g. run-admin.bat --port 8890).

Register it as an MCP server (e.g. in a Claude Desktop / Claude Code MCP config) pointing at the installed console script:

{
  "mcpServers": {
    "memai": {
      "command": "memai-mcp"
    }
  }
}

Admin dashboard

memai-admin (or python -m memai.admin) serves a local web dashboard over the same store, at http://127.0.0.1:8765 (loopback only; --host/--port/MEMAI_ADMIN_PORT to change). It is the human curation surface for everything the MCP tools do, plus the operations that only make sense for a person:

• Overview — live counts, confidence meter, per-type distribution, 30-day activity, vector coverage.

• Memories — hybrid search + filters (type/domain/status/confidence/ session), a per-memory record drawer (edit content with history, edit metadata with re-embedding, confidence triage, archive/restore, relations, line-level diffs of past edits, guarded purge), and multi-select bulk actions.

• Graph — force-layout of the relations graph; drag, zoom, click to inspect, and a link mode to create relations between two nodes.

• Domains — counts per domain, rename/merge (every affected row is re-embedded and audited), and spelling-drift detection (PROJ-1042 vs proj-1042).

• Maintenance — integrity/FTS/vector health checks, FTS rebuild, vector backfill/re-embed, orphan cleanup, VACUUM, timestamped backups (VACUUM INTO), a dedup-candidate review queue, and the audit trail.

It runs on Starlette + uvicorn, both already present as dependencies of the mcp SDK — no new requirements. Destructive-action parity with the MCP tools is kept: archiving is the default "delete", and purging demands the literal DELETE <uid> phrase typed into the UI.

Data location

%MEMAI_HOME%/memai.db if the MEMAI_HOME environment variable is set, otherwise ~/.memai/memai.db. Not tracked in git — it's user data, created on first run.

The default embedding model ships inside the package (src/memai/models/) so this is offline, CPU-only from the first run — no download, no huggingface-hub cache. Only an explicit MEMAI_EMBED_MODEL override that names a Hugging Face repo id touches the network (and then caches under ~/.cache/huggingface, same as before).