Mem Graph

MCP server for graph-relational memory: a v2 evolution of mem-sol that adds a graph layer (wikilinks, BM25 auto-linking, spreading activation, synaptic decay) on top of a layered memory model. Backed by better-sqlite3.

Purpose

Solo learning build exploring graph-relational memory as an MCP substrate. Not production-aimed, not benchmarked against peer systems; the goal is hands-on understanding of layered memory, wikilinks, and spreading activation.

mem-graph is the LLM's persistent memory between opencode sessions. It builds on mem-sol v1's relational foundation and adds:

• Layered memory model — five discrete layers (working, episodic, procedural, semantic, partner) with layer-aware decay and retrieval
• Wikilinks — markdown-style [[reference]] syntax in memory content creates hard, operator-curated edges
• BM25 auto-linking — on every insert, soft edges are auto-created to textually-overlapping memories in the same project
• Spreading activation — retrieval is text-match + neighborhood traversal with weight attenuation, not pure FTS
• Synaptic decay — synapse weights erode over time, with separate rates per layer pair and per connection type, and access-based exemption for hot edges

Install

Clone, install, and register as an MCP server:

git clone https://github.com/GoVanAI/mem-graph
cd mem-graph
npm install

Add this entry to your MCP client config (e.g., ~/.config/opencode/opencode.jsonc or Claude Code's MCP config):

{
  "mcpServers": {
    "mem-graph": {
      "command": "npm",
      "args": ["start", "--prefix", "/absolute/path/to/mem-graph"],
      "env": {
        "MEM_GRAPH_DIR": "/absolute/path/to/your/mem-graph-db"
      }
    }
  }
}

Replace both placeholder paths with absolute paths on your machine. The server reads MEM_GRAPH_DIR literally — ~ is not expanded at runtime. Default (without MEM_GRAPH_DIR) is ~/.local/share/mem-graph/memory.db.

Run (locally)

npm start

Tests

npm test           # run once, exits 0 on success
npm run test:watch # watch mode for development

108 tests across 9 files exercise the substrate in-memory via :memory: SQLite. Run takes ~500ms. See tests/ for fixtures and tests/helpers.ts for the createInMemoryDb() factory.

Configuration

The MCP reads:

• MEM_GRAPH_DIR — directory for the SQLite database. Default: ~/.local/share/mem-graph/. The DB file is memory.db inside. Override by setting the env var before launch.

Tools (27)

Group	Tools
SQL (4)	sql_query, sql_execute, sql_introspect, list_databases
Orient (4)	memory_overview, memory_prime, memory_projects, memory_categories
Search (5)	memory_search, memory_recent, memory_get, memory_changes, memory_stats
Write (7)	memory_add, memory_update, memory_supersede, memory_mark, memory_boost, memory_tag_add, memory_tag_remove
Graph (6)	memory_synapse_create, memory_synapse_traverse, memory_activate, memory_decay, memory_spread_stats, memory_stale
Import (1)	memory_import_from_mem_sol

memory_add write pipeline

On every memory_add:

1. Insert into memories (FTS5 triggers fire automatically)
2. Insert tags into memory_tag (junction table, no JSON)
3. Extract [[wikilinks]] from content, resolve to memory ids (id → title → slug), upsert synapses
4. Run BM25 auto-link against same-project memories, upsert bm25_auto synapses
5. Enforce 50/50 synapse cap (prune lowest-weight bm25_auto if exceeded)
6. Return: { id, wikilinks_resolved, broken_wikilinks, auto_links_created }

memory_activate (the headline graph tool)

Spreading activation retrieval. Inputs: query (FTS5 string), max_hop_depth (default 2), min_synapse_weight (default 0.3), limit_cap (default 20), land_on_layers (default all except working), pass_through_layers (default [semantic]), project_id (optional).

The recursive CTE carries a path column so the pass-through check can correctly verify "any ancestor in the path is a pass-through layer" (the v1 review's critical issue 1 is fixed here).

memory_stale (operational hygiene)

Find entries not accessed in N days. Inputs: days (default 30), project_id (optional), lifecycle (allow-list: permanent, milestone, ephemeral), layer (allow-list: working, episodic, procedural, semantic, partner), limit (default 50, max 500).

Each result row includes never_accessed: boolean (true when accessed_at IS NULL), making the cold-set cohort grep-able in JSON output. NULLs sort first — never-accessed entries surface at the top of the result set.

memory_tag_add / memory_tag_remove (quiet curation)

Tag curation tools that touch only the memory_tag junction table. Do NOT re-run wikilink extraction or BM25 auto-link. Do NOT bump accessed_at / access_count (tag curation is not a read). Idempotent: re-adding the same tag returns added: false; removing a missing tag returns removed: false.

memory_import_from_mem_sol (v1 → v2 migration)

One-shot migration from a mem-sol v1 SQLite DB. Pipeline: insert memories (FTS5 triggers fire) → parse JSON tags into memory_tag → two-pass wikilink extraction (handles forward references) → migrate v1 memory_links as wikilink synapses. Idempotent on (project_id, title). Auto-link is deferred to next activation.

Field-mapping highlights: project → project_id, relevance_score → importance_score, JSON-encoded tags → junction rows. Layer defaults to episodic for v1 entries (configurable). Source field remapped to import for all v1 origins.

Schema

See src/db.ts for the canonical DDL. Quick reference:

• memories — relational layer; columns: id, layer, title, slug, content, project_id, category, lifecycle, status, confidence, boost, summary, session_id, source, created_at, updated_at, accessed_at, access_count, importance_score, expires_at, refresh_strategy
• memory_tag — junction table, (memory_id, tag) PK with ON DELETE CASCADE
• synapses — graph edges; source_id, target_id, connection_type (wikilink / bm25_auto / parent_child), weight (0.0–5.0), access_count
• memories_fts — FTS5 mirror of memories (porter stemmer + 2/3-char prefix), kept in sync by triggers
• decay_matrix — (source_layer, target_layer, connection_type) → decay_rate; wildcard * for target_layer

Five layers

Layer	Purpose	Decay (vs same layer)
working	In-progress, in-flight	Aggressive (0.70 wikilink, 0.40 bm25)
episodic	Session events, time-anchored	Moderate (0.95 wikilink, 0.88 bm25)
semantic	Connective tissue, conceptual	Stable (0.99 wikilink, 0.93 bm25)
procedural	How-to, never-fade rules	Highly stable (0.995 wikilink, 0.98 bm25)
partner	User model, prefs	Most stable (0.999 wikilink, 0.97 bm25)

Locked decisions (v2 design doc §12 + review fixes)

#	Decision	Choice
D1	Tag storage	Junction table memory_tag
D2	Wikilink direction	author = source
D3	Cycle prevention	NOT EXISTS subquery
D4	Decay frequency	Tool exposed, runs via cron
D5	Synapse cap	50 in + 50 out per memory, enforced on insert
D6	Wikilink rendering	Auto-render to title in tool output
D7	access_count on synapses	Both memories and synapses
D8	ID format	Integer, autoincrement

Project context

• The MCP is project-local (this directory) but the database is user-global (~/.config/opencode/mem-graph/memory.db by default).
• Register in ~/.config/opencode/opencode.jsonc under the mem-graph MCP name; tools will be prefixed mem-graph_.
• Mem-graph coexists with mem-sol v1 — they are independent servers, independent databases.

Out of scope (explicitly deferred)

• cwd ↔ project binding
• Entry versioning / supersedes chain (only the basic memory_supersede tool exists)
• Tag-intersection queries (schema supports it via the junction table; no tool yet)
• knowledge.db (separate concern)
• Auto-link-on-read philosophy (R from analysis § 3.1, deferred to Tier 3+)

v0.2 / Tier 1 closure (2026-07-04)

Tier 1 implementation closed via loop-eng protocol, 6 iterations, 108 tests added. Specifically:

• R1 — Vitest suite covering wikilinks, auto-link, activate CTE, decay matrix, supersede; in-memory DB factory via exported SCHEMA_SQL + DECAY_MATRIX_SEED.
• R2 — memory_tag_add / memory_tag_remove quiet tools; no wikilink or auto-link re-run on tag change.
• R5 — memory_stale extended with lifecycle + layer filters; explicit never_accessed boolean surfaces the 28-row cold set.
• R3 — memory_import_from_mem_sol one-shot migration from v1 SQLite DB; idempotent on (project_id, title); preserves connections (not v1 type labels).
• R4 — category taxonomy documented (11 values: 9 standard + 3 first-class: commitment, open_question, trigger). No CHECK constraint added — agent-as-author migration is the right time to revisit.

Tool count grew from 24 → 27. Preserve-list (SQLite substrate, wikilinks-in-prose, 50-cap bm25-only pruning, 20-row decay matrix, 5-layer + 3-connection-type model) was held intact across all five iterations.

License

MIT