Lemma — Persistent Memory for LLMs via MCP

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Lemma is an MCP server that gives LLMs persistent, cross-session memory. Memories are injected automatically into every session — no explicit tool call needed. Knowledge evolves through use: frequently accessed memories strengthen, unused ones fade, and patterns are promoted into reusable skills. An autonomous intelligence layer runs in the background — detecting conflicts, suggesting actions, and auto-linking related knowledge.

Quick Start

Add Lemma to your MCP client configuration:

Claude Desktop (Windows): %APPDATA%\Claude\claude_desktop_config.json Claude Desktop (macOS): ~/Library/Application Support/Claude/claude_desktop_config.json Claude Code (Linux): ~/.claude.json or ~/.claude/settings.json opencode: ~/.config/opencode/opencode.json (Linux/macOS) or %APPDATA%\opencode\opencode.json (Windows)

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

Using @latest ensures npx always fetches the newest version.

Requirements: Node.js 20.0.0 or higher

CLI Usage

lemma -lib    # Library Mode: snapshot of your entire knowledge base
lemma -vis    # Visualizer: interactive memory graph in browser
lemma -vis -p 8080  # Visualizer on custom port (default: 3456)

Library Mode (-lib) outputs a full analysis of all memories, guides, relations, stale fragments, distill candidates, and suggested actions. Useful for periodic maintenance and review.

Visualizer (-vis) starts a local HTTP server and opens an interactive D3.js force-directed graph of your memory fragments in the browser. Nodes represent memories (sized by confidence + access count, colored by type). Links show relations and associations. All changes (edit, delete, link, unlink) write directly to the SQLite database in real-time. Cross-platform: works on macOS, Linux, and Windows.

How It Works

Memories are injected into tool descriptions via tools/list. The LLM starts every session already knowing its most important memories — works on every MCP client.

3-layer injection:

• Full content for top memories (token-budgeted)
• Summary index for remaining memories
• Active guides with learnings

Memory types: fact, pattern, lesson, warning, context

Knowledge pipeline: Memory (what you know, memory_add) → Pattern (type: "pattern") → Guide (how you work, guide_distill → guide_practice)

AGENTS.md injection: Lemma automatically injects a system prompt into your project's AGENTS.md, teaching the LLM how to use the memory system effectively. This ensures consistent behavior across all MCP clients.

Autonomous Intelligence

Lemma runs intelligence in the background — no manual triggering needed:

• Conflict Detection: Automatically checks new memories against existing knowledge for contradictions. Reports conflicts with suggestions to resolve.
• Proactive Suggestions: After adding memories or practicing guides, suggests actions like distilling patterns, merging duplicates, or refining low-performing guides.
• Auto-linking: Frequently co-read memories and topic-overlapping fragments are automatically connected with relations.

Manual deep analysis is also available via dedicated tools.

Tools (24)

Memory (11)

Guides (8)

Sessions (3)

Intelligence (4)

Configuration

Optional config at ~/.lemma/config.json:

{
  "token_budget": {
    "full_content": 5000,
    "summary_index": 1000,
    "guides_detail": 1000
  },
  "injection": {
    "max_full_content_fragments": 15,
    "max_summary_fragments": 30,
    "max_guides": 20
  },
  "virtual_session": {
    "timeout_minutes": 30
  }
}

File Locations

Files: lemma.db (SQLite), config.json, sessions/, logs/

Search

Lemma uses SQLite FTS5 full-text search for memory lookup, dedup, and topic overlap detection.

Architecture:

• searchAndSortFragments() — FTS5 full-text search, fallback to in-memory ranking
• findSimilarFragment() — FTS5 BM25-based dedup with keyword overlap fallback
• findTopicOverlaps() — FTS5 search + word overlap scoring for related fragment detection

Data Storage

All data is stored in a single SQLite database (~/.lemma/lemma.db):

Legacy JSONL files are automatically migrated on first run.

Security

All data is stored locally in ~/.lemma/. Nothing is sent to external servers. Secrets are automatically redacted from memory fragments (17 regex patterns for API keys, tokens, connection strings).

Documentation

• Development Guide — Architecture, project structure, testing
• Handlers Refactor — Targeted SQL migration plan
• Roadmap — v0.9, v0.10, v1.0 plans
• Research — Academic papers that influenced Lemma's design
• Changelog — Version history

License

MIT