Lean Ctx
Hook-oriented context engineering layer for AI dev — compress, remember, route, guard, and verify what crosses the agent/model boundary; upstream currently claims 60–90% token reduction, 81 MCP tools, and 30+ supported coding agents.
Repository: yvgude/lean-ctx (3,028 stars on 2026-06-30). Single local Rust binary vs rereading files, noisy shell output, repeated history, and session amnesia. The saved bookmark image captured v3.4.5, 49 tools, and "Open Source MCP Server" framing; current upstream is v3.8.17 with a broader request-proxy/addon/context-observability story. Source: yvgude/lean-ctx README, 2026-06-30
What it does
| Function | Effect |
|---|---|
| Compress | Trim redundant context before it hits the model |
| Remember | Persist session memory across turns |
| Route | Direct agent to relevant files/tools |
| Verify | Gate outputs before they compound |
Upstream claims 60–90% token reduction, cached re-reads near 13 tokens, prompt-cache-safe request compression, opt-in telemetry only, signed savings ledgers, and 80+ MCP tools. Benchmark on your repo before trusting the percentage; treat token reduction as a receipt, not a correctness guarantee. Source: X/@tom_doerr, 2026-05-08; Source: yvgude/lean-ctx README, 2026-06-30
Version snapshot
| Field | Snapshot |
|---|---|
| GitHub release | v3.8.17, published 2026-06-30. |
| npm | lean-ctx-bin@3.8.17 (latest), registry modified 2026-06-30 08:27 UTC. |
| GitHub | yvgude/lean-ctx, 3,028 stars, default branch main, HEAD 4c5393ce1712e62e676e0b44bd21258d0d155bfb, pushed 2026-06-30. |
| crates.io | Badge exists upstream, but crates.io API returned 403 during this review; use GitHub/npm as the verified snapshot and re-check crates when installing from Rust. |
| Current scope | README references 81 MCP tools, 30+ supported AI coding agents, shell hook, MCP server, request proxy, addons, memory, and observability. |
Complementary: rtk
@sdusteric's rtk (Rust CLI) strips git/test/lint/kubectl output via pre-bash hook (60–90% claim on shell boundary). rtk filters tool output; lean-ctx trims standing context — they stack. Source: X/@sdusteric, 2026-05-27
Stack fit (Kevin) — ENFORCED
Per CSS UI Enforcement: evaluate lean-ctx at repo bootstrap on every Kevin project before prompt tuning.
| When | Action |
|---|---|
| New repo enrollment | agent-docs init → install lean-ctx hooks → measure baseline vs trimmed sessions |
| Long agent loops | Pair with Browser Testing Skills — cheaper validate passes when context is lean |
| Dedalus monorepo | High file count = highest ROI; verify no hook hides critical architecture docs |
Install: follow README on github.com/yvgude/lean-ctx.
Timeline
- 2026-06-13 | Quality remediation: Context OS table, rtk complement, enforced bootstrap table. Source: Agent, 2026-06-13
- 2026-06-12 | README verification during coding-agents absorption (~2,307 stars). Source: yvgude/lean-ctx, 2026-06-12
- 2026-05-11 | Tier-1 registration; CSS UI Enforcement cross-link. Source: User, 2026-05-11
- 2026-06-30 | Deep bookmark artifact review refreshed the page from the saved release-card screenshot and current primary sources: screenshot showed
v3.4.5/49 tools; current verified state is GitHub/npmv3.8.17, 81 MCP tools in README, 3,028 stars, and HEAD4c5393ce1712e62e676e0b44bd21258d0d155bfb. Source: X bookmark artifact2052863824026366057; GitHub/npm, 2026-06-30