Lethe

Named for the river of forgetfulness in Greek mythology.

Local graph-based memory for Claude. Memories reinforce when used and fade when ignored.

What it does

• Remember facts, people, projects, preferences across conversations
• Recall by keyword — FTS5 full-text search with relevance ranking
• Decay — unused memories fade over time (ACT-R exponential decay, configurable half-life)
• Pin — important memories never decay
• Graph — memories connect to each other via typed relations
• Dashboard — web UI to browse, search, pin, and delete memories

Install

Claude Desktop (MCPB bundle)

Download lethe-0.1.0.mcpb from Releases. Double-click to install in Claude Desktop.

Build the MCPB bundle from source

# Install the MCPB packaging tool
npm install -g @anthropic-ai/mcpb

# Cross-compile + stage the bundle
make bundle

# Pack into a .mcpb file
mcpb pack bundle/

This produces lethe-0.1.0.mcpb — a single file you can double-click to install in Claude Desktop. It contains binaries for macOS (arm64 + amd64), Linux (amd64), and Windows (amd64).

Claude Code

# Build from source
make build

# Add to Claude Code
claude mcp add lethe -- ./bin/lethe --stdio

Manual (Claude Desktop JSON config)

{
  "mcpServers": {
    "lethe": {
      "command": "/path/to/lethe",
      "args": ["--stdio"]
    }
  }
}

Usage

Once installed, Claude will automatically have access to these tools:

Tool	What it does
remember	Store a fact, preference, or entity
recall	Search memories by keyword
forget	Soft-forget or permanently delete
pin / unpin	Toggle decay immunity
link / unlink	Create/remove relations between memories
get_context	Fetch the subgraph around a memory
update_memory	Edit an existing memory
list_recent	Recently created/reinforced memories
stats	Memory system statistics

Claude also gets three resources that auto-surface at session start:

• lethe://context/active — top 20 active memories
• lethe://stats/summary — compact stats
• lethe://schema/types — available node kinds and edge types

Dashboard

The leader process (first lethe instance) automatically starts a localhost web dashboard. Open it with:

lethe dashboard

Features: graph visualization, list view, timeline, fading memories section, pin/delete/edit, export/import.

Data

• Database: ~/Library/Application Support/lethe/memory.db (macOS), ~/.config/lethe/memory.db (Linux)
• Format: SQLite with WAL mode. Multi-process safe.
• Export: GET /api/export from dashboard, or use the dashboard UI
• Import: POST /api/import with JSON body

Decay model

Memories decay exponentially: S(t) = S₀ × e^(-λ × Δt) where λ = ln(2) / half_life_days.

• Default half-life: 30 days
• Reinforcement on retrieval: +1.0 (capped at 10.0)
• Pinned memories never decay
• Strength < 0.1 = "fading" (excluded from default search)
• Nothing is ever auto-deleted

Build

make build          # local binary → bin/lethe
make test           # run all tests
make lint           # go vet
make build-all      # cross-compile for darwin/linux/windows
make bundle         # build-all + copy to bundle/server/

Tech stack

• Go 1.23+
• SQLite via modernc.org/sqlite (pure Go, no CGO)
• MCP SDK: github.com/modelcontextprotocol/go-sdk
• Single static binary per platform