Lethe MCP server

LETHE

<!-- mcp-name: io.github.JesusGarcia9009/lethe -->

Live Ephemeral Token & History Engine — offload big tool outputs out of your LLM agent's context and recall them on demand, so long tasks cost fewer tokens.

🌍 This README is bilingual. English · Español

🔌 Use it in Claude Code or Codex (save tokens now)

LETHE ships as an MCP server. Two lines and your agent can move big outputs out of its context and recall them on demand — fewer tokens on every long task. / LETHE viene como servidor MCP. Dos líneas y tu agente saca outputs grandes del contexto y los recupera cuando los necesita — menos tokens en cada tarea larga.

Claude Code:

pip install "lethe-llm-context[mcp]"
claude mcp add lethe -- lethe-mcp

Codex: add an MCP block to ~/.codex/config.toml — see integrations/codex/mcp-config.md.

Then drop in the guiding skill so the agent archives on its own: integrations/claude-code/SKILL.md.

Tools exposed: lethearchive · letherecall · lethe_status. Full guide: integrations/claude-code/mcp-config.md.

▶️ See it work (no API key) / Míralo funcionar (sin API key)

python -m lethe.examples.mcp_demo

LETHE — offload big tool outputs, recall on demand, save tokens

The agent runs 4 commands. Each returns a wall of text:

  → build.log               857 tok in context  —archive→  stub '[paged: build.log | handle=6d48a1c2]'
  → pytest.txt              479 tok in context  —archive→  stub '[paged: pytest.txt | handle=1e56b0f4]'
  → db_dump.json            829 tok in context  —archive→  stub '[paged: db_dump.json | handle=ec02...]'
  → trace.txt               414 tok in context  —archive→  stub '[paged: trace.txt | handle=d888...]'

lethe_status:  4 blocks archived, 2579 tokens moved out of context

30 steps later the agent needs a buried fact. It recalls by keyword:

  lethe_recall("launch_code")  →  found launch_code = 4242 (rehydrated losslessly from the archive)

  Context window cost
    without LETHE :  2579 tok  (everything stays resident)
    with LETHE    :    38 tok  (only tiny stubs remain)
    saved         :  2541 tok  (-99%)

This runs the same logic the MCP tools use — lethearchive / letherecall / lethe_status.

English

What LETHE is (today, honestly)

When an LLM agent runs a long task (tens to hundreds of steps), its context window fills with material that was useful but no longer is: stale tool outputs, files read 30 steps ago, big JSON dumps. That means more tokens per turn, higher cost, and eventually the context ceiling.

LETHE gives the agent an external, lossless scratch store so that heavy content lives outside the context window and only a tiny handle stays inside. Two ways to use it:

Shortened. The full README is on GitHub.