Memory MCP

A Model Context Protocol (MCP) server that gives AI coding agents persistent, evolving knowledge about a codebase. Instead of starting cold every session, agents can store and retrieve observations about architecture, conventions, gotchas, and recent work context.

Tools

Hidden tools (still callable, not in the catalog — agents learn about them from hints/errors): memory_list_lobes (lobe paths and stats), memory_stats (entry counts, freshness, storage), memory_diagnose (server health, crash history, recovery steps)

Related MCP server: @brainfeather/mcp

Knowledge Topics

Global topics (user, preferences) are stored in a shared global store at ~/.memory-mcp/global/ and are accessible from all lobes. This means your identity and coding preferences follow you across every repository without duplication.

Smart Surfacing

• Dedup detection: When you store an entry, the response shows similar existing entries in the same topic (>35% keyword overlap) with consolidation instructions

• Preference surfacing: Storing a non-preference entry shows relevant preferences that might conflict

• Ephemeral review gate: Likely-ephemeral content is blocked before persistence by default. Re-run memory_store(..., durabilityDecision: "store-anyway") only when you intentionally want to keep it.

• Piggyback hints: memory_correct suggests storing corrections as reusable preferences

• memory_context: Describe your task in natural language and get ranked results across all topics with topic-based boosting (preferences 1.8x, gotchas 1.5x)

Smart Filter Syntax

memory_query supports a filter mini-language for precise searches:

Filters use stemmed matching, so reducers matches reducer and exceptions matches exception.

Quick Start

# Install dependencies
npm install

# Build
npm run build

# Run tests
npm test

Configuration

Config File (Recommended)

Create a memory-config.json file next to the memory MCP server:

{
  "lobes": {
    "workspace-mcp": {
      "root": "$HOME/git/personal/workspace-mcp",
      "budgetMB": 2
    },
    "workrail": {
      "root": "$HOME/git/personal/workrail",
      "budgetMB": 2
    }
  }
}

Note: memoryDir is optional. When omitted, storage auto-detects to .git/memory/ for git repos.

What's a "lobe"? Each repository gets its own memory lobe -- a dedicated knowledge scope. Think of it like brain regions: the "workrail lobe" stores knowledge about workrail, the "workspace-mcp lobe" stores knowledge about workspace-mcp.

Benefits:

• Portable ($HOME and ~ expansion works across machines)

• Discoverable (use memory_list_lobes to see what's configured)

• Easy to extend (just add a new lobe entry)

Environment Variables (Fallback)

If no memory-config.json is found, the server falls back to environment variables:

Adding a New Lobe

1. Edit memory-config.json (create if it doesn't exist)

2. Add lobe entry:

   {
   "my-project": {
     "root": "$HOME/git/my-project",
     "budgetMB": 2
   }
   }

3. Restart the memory MCP server

4. Verify: Use memory_list_lobes to confirm it loaded

The agent will see the new lobe in tool descriptions and can immediately use it with memory_store(lobe: "my-project", ...).

MCP Client Registration

With memory-config.json (recommended):

{
  "mcpServers": {
    "memory": {
      "command": "node",
      "args": ["/path/to/memory-mcp/dist/index.js"]
    }
  }
}

The server reads memory-config.json automatically -- no env vars needed.

Environment Variable Mode

{
  "mcpServers": {
    "memory": {
      "command": "node",
      "args": ["/path/to/memory-mcp/dist/index.js"],
      "env": {
        "MEMORY_MCP_WORKSPACES": "{\"android\":\"/path/to/android\",\"ios\":\"/path/to/ios\"}"
      }
    }
  }
}

Storage Location

Knowledge is stored as human-readable Markdown files -- one file per entry. The storage location is auto-detected with the following priority:

1. Explicit memoryDir config -- if set in memory-config.json or MEMORY_MCP_DIR, uses that path

2. Git-native (default) -- <git-common-dir>/memory/ using git rev-parse --git-common-dir. This ensures:

   • Invisible to git -- .git/ contents are never tracked, no .gitignore needed

   • Shared across worktrees -- all worktrees of the same repo share one memory store

   • Worktree/submodule safe -- resolves to the common .git/ directory regardless

3. Central fallback -- ~/.memory-mcp/<lobe-name>/ for non-git directories

Use memory_stats or memory_list_lobes to see where memory is stored for each lobe.

File Structure

Each entry gets its own file. Recent-work entries are scoped by branch.

.git/memory/
  architecture/
    arch-e8d4f012.md              # One entry per file
  conventions/
    conv-a1b2c3d4.md
  gotchas/
    gotcha-7k3m9p2q.md
  recent-work/
    main/                          # Branch-scoped
      recent-f5e6d7c8.md
    feature-messaging-refactor/    # Sanitized branch name
      recent-9i0j1k2l.md
  modules/
    messaging/
      mod-4d5e6f7g.md

~/.memory-mcp/global/              # Global store (shared across all lobes)
  user/
    user-3f7a2b1c.md              # Personal info
  preferences/
    pref-5c9b7e3d.md              # Coding opinions & corrections

Concurrency Safety

Each entry is its own file with a random hex ID. Two MCP processes (e.g., Firebender + Cursor) writing different entries to the same repo never conflict -- they write to different files. The store reloads from disk before every read to pick up changes from other processes.

Branch-Scoped Recent Work

Recent-work entries are automatically tagged with the current git branch and stored in a branch-named subdirectory. memory_query filters recent-work to the current branch by default. Use branch: "*" to see recent-work from all branches.

Entry Format

# Build System & Language
- **id**: arch-3f7a2b1c
- **topic**: architecture
- **confidence**: 0.70
- **trust**: agent-inferred
- **created**: 2026-02-18T12:00:00.000Z
- **lastAccessed**: 2026-02-18T12:00:00.000Z

Detected: Node.js/TypeScript project (npm)

Trust Levels

Resilience

The server uses a degradation ladder to stay useful even when things go wrong:

• Running -- all lobes healthy, full functionality

• Degraded -- some lobes failed to initialize but healthy ones continue working. Failed lobes report specific recovery steps via memory_diagnose.

• Safe Mode -- all lobes failed. Only memory_diagnose and memory_list_lobes work, giving you enough information to fix the problem.

Crash journaling: On uncaught exceptions, the server writes a structured crash report to ~/.memory-mcp/crashes/ before exiting. The next startup surfaces the crash in memory_context() (briefing mode) with recovery steps. Use memory_diagnose(showCrashHistory: true) to see the full history.

Argument Normalization

Agents frequently guess wrong parameter names. The server silently resolves common aliases to avoid wasted round-trips:

Wildcard scope aliases (all, everything, global, project) resolve to *.

Architecture

types.ts          Domain types (discriminated unions, parse functions)
store.ts          MarkdownMemoryStore (CRUD, search, bootstrap, briefing)
text-analyzer.ts  Keyword extraction, stemming, similarity (stateless)
normalize.ts      Argument alias resolution (pure)
formatters.ts     Response formatters for tool handlers (pure)
config.ts         3-tier config loading (file > env > default)
git-service.ts    Git operations boundary (injectable for testing)
crash-journal.ts  Crash report lifecycle (build, write, read, format)
index.ts          MCP server, tool handlers, startup, migration

Design

See ideas/codebase-memory-mcp-design-thinking.md for the full design thinking document with 67 ideas, 5 concept packages, pre-mortem analysis, and test plan.