memsem

Semantic memory for AI agents — remembers what matters, knows what to forget. One command to install. Works in every project, for every AI. 100% local.

Why — when big memory systems already exist?

They exist, and they got the hard parts right: vector stores (mem0), temporal knowledge graphs (Zep / Graphiti), agent frameworks (MemGPT / Letta). But they all share the same three flaws:

1. Brute storage, no structure. They keep what you throw at them, and retrieval is a similarity search over everything. The AI doesn't know where to look — so it looks everywhere, and the noise drowns the signal.

2. No precision. A fuzzy match is a fuzzy match: almost-right memories fill the context budget and waste tokens.

3. No self-correction. A fact contradicted months ago stays as strong as the day it was written.

memsem fixes exactly these three things:

• 🧭 It knows where to search. Every session starts with a routing card (memory-index.md): themes + keywords, injected into the context. The AI routes by theme, crosses projects, and only pays for what it needs. Hierarchical themes + a live focus list keep the session's active branches at full priority — the rest is attenuated, never lost.

• 🎯 It is precise. Strict lexical search by default (50% word-match threshold, no graph propagation unless you explicitly ask) — a query returns the right facts, ranked by dynamic priority (importance × confidence × recency × frequency). Precision is measured, not assumed: P@3 0.958 on the reference benchmark (51 facts, 20 queries, scripts/bench.mjs, results in DESIGN.md §11).

• 🔄 It corrects itself. Contradictions fade the old fact instead of overwriting it ("I drank milk for years… wait, lactose intolerant") — history is always kept, critical facts (≥ 0.9) are protected. Background agents extract durable facts at session end, consolidate small facts into patterns, and recalibrate priorities — only when the memory stays at least as searchable.

All the big-system promises, minus their flaws: one command, 100% local, and your memory stays yours — never committed, per-user, shared across all your repos.

Related MCP server: local-memory-mcp

See it work

Install once, let it run. This is a real session on a throwaway database — your actual memory is never touched (node scripts/demo.mjs):

=== memsem — demo on a temporary database ===
(your real memory in ~/.memory-mcp stays untouched)

1. The AI writes durable facts (memory_add_many)
   → 4 facts written

2. Strict search (lexical): memory_search { query: 'milk' }
   → user → drinks → milk

3. Semantic search (relax, local embeddings): memory_search { query: 'cheese', relax: true }
   No shared word with « lactose » — the local semantic index (Ollama) bridges it
   → lactose → is-present-in → cheese, yogurt, cream
   → user → is-intolerant-to → lactose
   → user → drinks → milk

4. Soft supersession: the AI learns you no longer drink milk
   → conflict: true, old fact faded (faded: [1])

5. Search now returns the current fact
   → user → drinks → no more milk (lactose intolerant)
   → user → drinks → milk

Stats: 5 active memories, semantic index OK (mxbai-embed-large)

Privacy — your memory is yours

• 100% local — stored in ~/.memory-mcp/memory.db on your machine. No cloud, no telemetry, nothing leaves your computer.

• Never committed — the database lives outside every repository. Clone a public repo, push code, share screenshots: your memory stays with you. Each user has their own memory.

• The memory follows you, not your projects — the same base is shared across all your repos. Create a new folder, a new repo: the memory is still there.

Install

opencode — one line

Add to opencode.json (project or ~/.config/opencode/opencode.json):

{ "plugin": ["memsem"] }

That's it. The plugin registers the MCP server, injects the memory protocol and the memory index into every session, grants the needed permissions, and runs the background agents. Restart opencode.

Claude Code — one command

npx -y memsem setup

This registers the MCP server (claude mcp add memory -- npx -y memsem) and adds a "memsem memory" block to ~/.claude/CLAUDE.md pointing to the full protocol.

Or install it with AI: just paste into Claude:

Install the memsem persistent memory: run npx -y memsem setup, read ~/.memsem/memory-protocol.md, and apply the protocol.

Any MCP client

npx -y memsem

The server speaks MCP over stdio. Point any MCP-capable host at it and inject memory-protocol.md into the host's instructions (e.g. as AGENTS.md) to make the AI autonomous.

Universal installer

npx -y memsem setup        # detects and configures your hosts (opencode, Claude)
npx -y memsem setup --help # see options

Idempotent, safe, reversible (--uninstall).

How it works

The memory lifecycle — every fact follows the same path:

flowchart LR
    W["memory_add — subject → predicate → object"] --> R["repeated → confidence ↑ frequency ↑"]
    W --> P["priority = f(importance, confidence, recency, frequency)"]
    R --> S{"contradiction?"}
    S -- yes --> F["old fact fades progressively"]
    F --> A["archived — history always kept"]
    S -- no --> K["kept, reinforced"]
    A --> J["pinned & critical (≥ 0.9) are protected"]

• Atomic facts — every memory is a subject → predicate → object triple with importance, confidence, frequency, tags, theme, provenance, trust and evidence.

• Themes & focus — hierarchical themes (food/drinks) are the routing map; a search by theme crosses all projects. The focus list keeps the session's active themes at full priority.

• Dynamic priority — 0.45 × importance + 0.25 × confidence + 0.2 × recency + 0.1 × frequency. A critical fact beats a recurring pattern.

• Soft supersession — contradictions fade the old fact (confidence decays) until it archives under a threshold. History is always kept.

• Semantic index (optional) — each fact is embedded locally (mxbai-embed-large via Ollama); relax: true searches add cosine similarity (threshold 0.5). Without Ollama, everything works identically — strict lexical search.

• Evidence and time — inferred, verbatim and verified trust states keep a short evidence trail; recorded_at is separate from valid_from / valid_until, with historical asOf queries.

• Review and scope — uncertain facts can stay pending; rejection blocks their normalized value, project scope is isolated by default, and cross-project search is explicit.

Comparison

Comparison as of Aug 2026, from public docs; capabilities evolve — verify before choosing.

Command line

Everything that can be done through MCP can be done from a terminal:

memsem list [--theme x] [--project p] [--limit n] [--all]   # read your memory
memsem edit <id> [--object "..."] [--importance 0.6] [...]  # fix a fact by hand (audited)
  memsem forget <id> [--yes]                                  # archive a fact (confirm)
  memsem purge <id> [--yes]                                   # permanently erase a fact (confirm)
memsem doctor [--limit n] [--hours h]                       # most-modified facts — spot drift
memsem export [--output f] [--project p]                    # full JSON dump
memsem import <file.json>                                   # restore / merge a dump
memsem setup [--host opencode|claude]                       # install for your hosts

Manual fixes are written to the audit journal — memsem doctor shows them too.

Configuration

Tunable constants (priority weights, thresholds, fade factors, model…) live in src/config.ts. Override any of them in ~/.memsem/config.json (or $MEMSEM_CONFIG), deep-merged with validation:

{ "priority": { "importance": 0.4, "confidence": 0.3 }, "minLexical": 0.4 }

Settings are documented and validated by a benchmark (scripts/bench.mjs — 51 facts, 20 queries, P@k/R@k across constant sets; results in DESIGN.md §11).

Durability

The database is versioned and migrated automatically at startup (schema_migrations), with an automatic backup before any migration (~/.memory-mcp/backups/, last 5 kept). WAL mode is on — a crash mid-write leaves the database intact. Full dumps and restores via memsem export / memsem import.

Documentation

• memory-protocol.md — the protocol injected into your AI: how it writes, searches, and maintains memory automatically.

• DESIGN.md — full design: vision, principles, the lactose case study, constant calibration, roadmap.

• scripts/demo.mjs — reproduce the demo above on a throwaway database.

Roadmap

• Semantic index (local Ollama embeddings)

• Episodic memory + session extraction

• Hippocampus consolidation + pairwise scoring judge

• Universal opencode plugin + memsem setup

• Versioned migrations + automatic backup + export/import

• Configurable constants, validated by a benchmark

• Secure judge: dry-run, audit journal, guardrails, memsem doctor

• CLI: list / edit / forget — fix a fact by hand

• Evidence contract, temporal validity, candidate review, audit and confirmed purge

• Obsidian bridge: export/import memory as readable markdown notes

• Multi-hop graph propagation

License

MIT — free for anything. Your memory stays yours.