lean-ctx

Control what your AI can see.

LeanCTX — Context Engineering Layer for AI Coding Agents

LeanCTX — short for Lean Context — is the context engineering layer for AI coding agents. It runs locally alongside your coding agent, helping it read repositories, run development commands, and send focused context to the model: it decides what agents read, compresses what they send (an optional local proxy shrinks every request — system prompt, history and tool results — prompt-cache-safe), remembers what they learn, guards what they touch — and proves what they save with a signed, verifiable savings ledger. The result: 60–90% fewer tokens. Zero config required. Local-first.

Problem	With LeanCTX
Repeated file reads: ~2000 tokens each	Cached re-reads: ~13 tokens
Raw git status: ~800 tokens	Compressed: ~120 tokens
Every turn re-sends the whole history	Proxy compresses each request, prompt-cache-safe
Context resets every chat	Session memory persists across chats
No visibility into context usage	Real-time dashboard + budget control

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Control what your AI can see. LeanCTX — short for Lean Context — is the context engineering layer for AI coding agents: one local Rust binary that helps agents read repositories, run development commands, compress context sent to the model, remember what they learn, guard what they touch — and prove what they save.

Token savings are the receipt. Intelligence is the product. Works with Cursor, Claude Code, Copilot, Windsurf, Codex, Gemini and 30+ other agents — no config needed.

Why developers use LeanCTX

• Longer useful coding sessions — less context waste = more room for actual code reasoning
• Lower API costs — 60–90% fewer tokens on reads and shell output, cached re-reads cost ~13 tokens
• No more "I already showed you this file" — session memory persists across chats
• Works with your existing setup — one lean-ctx setup command, no config changes needed
• Full visibility — see exactly where your context window budget goes
• Model-agnostic & yours — swap OpenAI/Anthropic/Gemini freely; your context and memory stay local and portable, never locked in a vendor's black box

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Why now — own your context

Models are converging on commodity. The durable edge isn't which model you call — it's your context: what your agents read, what they remember, and what you can prove. And the layer that optimizes and owns that context can't come from the vendor that bills per token or keeps your memory in a black box — it has to sit on your side.

That's the shift behind "agent entities" that live in your chat and remember your company (Claude in Slack, ClickUp Brain): a context login, not a model login — you end up renting your own company knowledge back. LeanCTX is the opposite layer. It keeps the moat yours: local-first, portable (.ctxpkg), and model-agnostic — swap OpenAI, Anthropic or Gemini without losing context or cache. Own your context; don't rent it back.

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What it does — the four dimensions of context

LeanCTX treats context as a managed resource, not an afterthought. One binary covers the four dimensions that decide how well an AI agent actually performs:

1. Compression — input efficiency

Your AI agent reads files and runs commands. LeanCTX compresses both automatically.

• File reads: 10 read modes (full, map, signatures, diff, lines:N-M, density:X, …) — cached re-reads cost ~13 tokens
• Target density (density:0.4): SDE-style budget compression — keeps the highest-entropy lines until ~40% of the original tokens remain, deterministic
• JIT disclosure: signatures carries line spans and points at lines:N-M for targeted expansion — outline first, bodies on demand
• Shell output: 95+ shell-output patterns compress git, npm, cargo, docker, kubectl, terraform and more (270 passthrough rules)
• Tree-sitter AST: structural understanding for 27 languages — not just text compression
• Reversible by design (CCR): compression never discards content — pruned or truncated payloads move to a content-addressed store with a deterministic handle, so the model can pull the original bytes back on demand via ctx_expand, ctx_retrieve, an in-band marker, or GET /v1/references/{id}. Five recovery paths →

2. Routing — the right fidelity per read

Not every file needs the same depth. LeanCTX sends the signal, not the noise.

• 10 read modes: from full content down to AST signatures and entropy-filtered views
• Adaptive ModePredictor: learns the optimal read mode per file type from past sessions
• IntentEngine: classifies query complexity so simple lookups stay cheap

3. Memory — context that persists

Context doesn't disappear between chats anymore.

• Session memory (CCP): persist task/facts/decisions across chats — structured recovery queries survive compaction
• Knowledge graph: temporal facts with validity windows, episodic + procedural memory
• Property Graph: multi-edge code graph (imports, calls, exports, type_ref) powers impact analysis and search ranking
• Yours, not the vendor's: memory stays local and portable — export it as a .ctxpkg package and move it across machines or models, instead of locking it in a vendor's black box

4. Verification — control what reaches the model

Performance is accuracy, not just speed. You stay in control of the window.

• Context Manager: browser dashboard with real-time token tracking, compression stats, utilization gauge
• Budgets & SLOs: profiles, roles, per-agent budgets, and throttling policies
• Context Proof (ctx_proof, ctx_verify): 4-layer verification engine with CI drift gates

• Web & Research (ctx_url_read): pull a public web page, PDF, or YouTube transcript into context as compressed, citation-backed text — facts/quotes return claims with a confidence score + source URL, relevance-ranked research-compression distils to a token budget, SSRF-guarded (http/https only)
• Graph-Powered Intelligence: hybrid search (BM25 + embeddings + graph proximity via RRF), incremental git-diff updates
• LSP Refactoring (ctx_refactor): language-server-powered rename, references, go-to-definition via rust-analyzer, typescript-language-server, pylsp, gopls
• Multi-Agent (ctx_agent, ctx_handoff): agent handoff with context transfer bundles, diary system, synchronized shared state
• Archive Full-Text Search (ctx_expand search_all): FTS5-powered cross-archive search over all previously archived tool outputs
• PR Context Packs: lean-ctx pack --pr builds a PR-ready context pack (changed files, related tests, impact, artifacts)
• Context Packages: lean-ctx pack create bundles Knowledge + Graph + Session into portable .ctxpkg files with SHA-256 integrity
• Context Time Machine: lean-ctx snapshot create|list|show|verify|restore|publish|import — git-anchored, ed25519-signed snapshots of the layer state (lineage, ledger Φ, ROI, session) on an append-only timeline; replay them in the dashboard, restore to resume a session (and --git to check out the commit), or publish/import a signed snapshot to share it (concept →)
• Observability: lean-ctx gain --live for real-time savings, lean-ctx wrapped for weekly/monthly summaries (gain --svg/--share for a shareable card or self-hostable page), lean-ctx watch for TUI monitoring
• Verified savings: lean-ctx savings is an auditable, per-event ledger (tokenizer transparency, bounce-netting, tamper-evident SHA-256 chain) — local-only, on by default
• HTTP mode: lean-ctx serve for Streamable HTTP MCP + /v1/tools/call (used by the Cookbook + SDK)

Addons — run the ecosystem through one gateway

You don't have to choose between LeanCTX and the other context tools you already like. An addon wraps any MCP server in a tiny lean-ctx-addon.toml manifest; LeanCTX runs it behind its gateway with one command, then treats what it returns like your own reads instead of just proxying it.

lean-ctx addon search memory   # browse the registry by category
lean-ctx addon add headroom    # installs the upstream package + wires the MCP server, on add
lean-ctx addon list            # what's wired into your gateway

• One command to add — addon add <name> installs the upstream package via its native manager (uv, pip, cargo, npm, brew, dotnet) and wires the MCP server into your gateway. No fork, no recompile.
• Folded in, not just proxied — opt-in post-processing runs addon output through the same pipeline as your code: compress to a budget, spill oversized blobs to a ctx_expand handle, index into BM25 / graph / knowledge. Typed adapters route specific tools straight into ctx_expand, ctx_callgraph and ctx_knowledge.
• Untrusted by default — every addon's output is scrubbed for secrets and tagged untrusted before it reaches the model. Always on, not a flag.
• You stay in control — pin a machine or fleet to verified-only, an allowlist, or off entirely via one [addons] policy a single repo can't override.

The registry spans compression (Headroom, Sophon), code intelligence (Repomix, Serena), memory (Mem0, Cognee, Letta) and reasoning (Sequential Thinking). See the addon guide or browse them all.

Where it's going

LeanCTX is growing from a single context layer into a full cognitive context layer for whole teams: version-controlled context strategy, one unified graph, and a governance layer across many agents.

• Context Time Machine → hosted history — the snapshot engine, dashboard replay, restore, and signed file-based share/import have shipped (see above); next is a ctxpkg.com registry for hosted, versioned context history and a side-by-side model-view ｜ git-diff replay. The temporal axis through everything LeanCTX does — it decides, remembers, guards, proves, and replays. (concept →)
• Context as Code — declarative pipelines, profiles, and policies in TOML, versioned like infrastructure
• Unified Context Graph — code, tests, commits, CI runs, and knowledge entries in a single semantic graph
• Agent Harness — roles, budgets, and tool permissions for multi-agent governance
• Context Observability — SLOs on context consumption, anomaly detection, OpenTelemetry / Prometheus export

The full roadmap lives in VISION.md.

How it works (30 seconds)

LeanCTX works on two planes — what your agents read and what they send to the model:

read path:   AI tool  →  (MCP tools + shell)  →  lean-ctx  →  your repo + CLI
wire path:   AI tool  →  lean-ctx proxy        →  model provider   (every request, compressed)

• MCP server (read path): exposes ctx_* tools (read modes, caching, deltas, search, memory, multi-agent)
• Shell hook (read path): transparently compresses common commands so the LLM sees less noise
• Request proxy (wire path, opt-in): lean-ctx proxy enable puts a local proxy between your agent and the model that compresses every request — system prompt, full history and tool results — prompt-cache-safe, with measured USD spend. It can also pin one reasoning-effort level across OpenAI, Anthropic & Gemini (proxy.effort) without breaking that cache, cut output tokens with a cache-safe verbosity steer plus a measured holdout, and relocate volatile fields (dates, UUIDs, commit SHAs) out of the cacheable prefix so a stable system prompt finally caches. Every rewrite is reversible (content-addressed recovery) and byte-stable by contract. Same layer as a standalone request-compression proxy (e.g. Headroom) — you don't need one on top.
• Property Graph: multi-edge code graph powers impact analysis, related file discovery, and search ranking
• Session memory: persists state with structured recovery so long-running work never "cold starts"
• Context Manager: browser dashboard for real-time visibility into what's in your context window

Get started (30 seconds)

# 1) Install (pick one)
curl -fsSL https://leanctx.com/install.sh | sh      # universal (no Rust needed)
brew tap yvgude/lean-ctx && brew install lean-ctx    # macOS / Linux
npm install -g lean-ctx-bin                          # Node.js
cargo install lean-ctx                               # Rust
pi install npm:pi-lean-ctx                           # Pi Coding Agent

# 2) One-command setup for your agent
lean-ctx wrap cursor      # or: wrap claude / wrap codex / wrap vscode

# Done. Savings appear after your AI's first lean-ctx call.
lean-ctx gain

lean-ctx wrap installs shell hooks, registers the MCP server, sets up agent hooks, starts the daemon, and verifies the connection — all in one command. Undo anytime with lean-ctx unwrap cursor.

lean-ctx onboard          # connect all detected AI tools (zero prompts)
lean-ctx setup            # interactive wizard with every option

Building from source on Windows? Clone the repo and run ./install.ps1 in PowerShell — it builds the release binary and installs it into Cargo's bin directory (pass -BuildOnly to build without installing).

• Disable immediately (current shell): lean-ctx-off
• Run a single command uncompressed: lean-ctx -c --raw "git status"
• Only activate in AI agent sessions: set shell_activation = "agents-only" in ~/.config/lean-ctx/config.toml
• Per-project config override: create .lean-ctx.toml in your project root (auto-merged with global config)
• Docker projects sharing /workspace: create .lean-ctx-id with a unique name to prevent context collisions
• Update: lean-ctx update
• Diagnose (shareable): lean-ctx doctor --json

Use it from your own code (SDKs)

Beyond the CLI, lean-ctx ships published libraries so you can call it directly from your app.

Drop-in prompt compression — lean-ctx-sdk (npm). Compress a chat-style messages array before it reaches any model — deterministic and prompt-cache friendly; images, tool-calls and ids pass through untouched.

# pip install lean-ctx-sdk
from lean_ctx import compress
messages = compress(messages, model="claude-sonnet-4")

// npm install lean-ctx-sdk
import { compress } from "lean-ctx-sdk";
messages = await compress(messages, { model: "gpt-4o" });

Framework adapters included (LiteLLM, LangChain, Vercel AI SDK). → compress() cookbook

Thin /v1 contract clients — lean-ctx-client (npm · crates.io). Wrap the full /v1 tool, event and session API over the process boundary — never links the engine, so it stays stable as lean-ctx evolves.

pip install lean-ctx-client     # Python (imports as `leanctx`)
npm install lean-ctx-client     # TypeScript / Node
cargo add lean-ctx-client       # Rust

Start the server with lean-ctx serve, then point a client at it. → API reference

Real-world scenarios

LeanCTX grows with you. Below are the journeys most people actually take — each links to a complete, function-by-function walkthrough in the Reference (every CLI command and all 82 MCP tools are documented there).

🟢 Your first 30 seconds

"I just installed it — now what?"

lean-ctx wrap cursor  # one-command setup for your agent
lean-ctx doctor       # confirm you're wired up

One command installs hooks, MCP registration, and verifies the connection. → Journey 1 — Setup & Onboarding

📖 Coding every day

"Stop re-reading the same files."

lean-ctx read src/server.rs -m map   # API surface, ~13 tok on re-read
lean-ctx -c "git status"             # compressed shell output

Your agent reads less and searches smarter — automatically. → Journey 2 — Daily Use

🧠 Resume where you left off

"My new chat forgot everything."

lean-ctx overview                    # task-aware project recap
lean-ctx knowledge recall "auth"     # facts that survive resets
lean-ctx knowledge consolidate       # import session + compact lifecycle
lean-ctx knowledge consolidate --all # compact every project store

Session memory + a project knowledge graph persist across chats. → Journey 3 — Memory & Knowledge

🗺️ Understand a new codebase

"Where does this function ripple to?"

lean-ctx graph impact src/auth.rs    # blast radius
lean-ctx smells scan                 # code-smell hotspots

A multi-edge property graph powers impact analysis + ranked search. → Journey 4 — Code Intelligence

🔌 Providers & multi-repo

"Pull in GitHub issues and our Postgres schema."

lean-ctx provider list
lean-ctx serve --root ./api --root ./web   # multi-repo

External data flows through the same consolidation pipeline. → Journey 5 — Advanced & Integrations

🛠️ Keep it healthy

"Update, fix, or cleanly remove."

lean-ctx doctor --fix
lean-ctx update

Self-healing diagnostics; surgical uninstall that only removes its own blocks. → Journey 6 — Lifecycle & Troubleshooting

🎛️ Take control of the window

"Budget my context like a pro."

lean-ctx plan "refactor billing" --budget 8000
lean-ctx compile --mode balanced

Phi-scored planning + knapsack compilation + a context ledger. → Journey 7 — Context Engineering

🤝 Run a team of agents

"Planner + coder + reviewer on one repo."

ctx_agent action=register role=dev
ctx_handoff action=create        # baton-pass with full context

Shared message bus, diaries, knowledge, and deterministic handoffs. → Journey 8 — Multi-Agent Collaboration

🏢 Share across a team / CI

"One shared index, headless in pipelines."

lean-ctx team serve --config team.toml
lean-ctx bootstrap            # zero-prompt CI setup

Scoped tokens, optional cloud sync, verifiable context gates. → Journey 9 — Team, Cloud & CI

🎚️ Tune & govern

"Make it behave exactly how we want."

lean-ctx compression standard
lean-ctx harden               # enforce token discipline

Compression levels, tool profiles, themes, and rules governance. → Journey 10 — Customization & Governance

📊 Prove the payoff

"Show me the numbers."

lean-ctx gain --deep          # savings, cost, per-agent, heatmap
lean-ctx wrapped              # shareable recap (also: gain --svg / gain --share)
lean-ctx savings              # verified per-event ledger (auditable; savings verify)

All analytics live in the CLI/dashboard — never burning agent tokens. → Journey 11 — Analytics & Insights

📚 The full reference

"I want to read everything."

Every command and all 83 MCP tools, organized as user journeys, plus appendices for the CLI map, MCP tools, and paths & config. → Reference index

Supported IDEs & AI tools

LeanCTX is a standard MCP server, so it works with any MCP-compatible client. Two integration modes are auto-selected per agent:

Mode	How it works	Best for
Hybrid	MCP for cached reads (~13 tokens) + shell hooks for command compression	Agents with shell access (Cursor, Claude Code, Codex, ...)
MCP	All 83 tools via MCP protocol, no shell hooks	Protocol-only agents (JetBrains, VS Code, Zed, ...)

Agent compatibility matrix

Agent	Hybrid	MCP	Setup
Cursor	●		lean-ctx init --agent cursor
Claude Code	●		lean-ctx init --agent claude
CodeBuddy	●		lean-ctx init --agent codebuddy
Augment CLI / VS Code	●		lean-ctx init --agent augment
Codex CLI	●		lean-ctx init --agent codex
Grok	●		lean-ctx init --agent grok
Gemini CLI	●		lean-ctx init --agent gemini
Windsurf	●		lean-ctx init --agent windsurf
GitHub Copilot	●		lean-ctx init --agent copilot
CRUSH	●		lean-ctx init --agent crush
Hermes	●		lean-ctx init --agent hermes
OpenCode	●		lean-ctx init --agent opencode
Pi	●		lean-ctx init --agent pi
Qoder	●		lean-ctx init --agent qoder
Amp	●		lean-ctx init --agent amp
Cline	●		lean-ctx init --agent cline
Roo Code	●		lean-ctx init --agent roo
Kiro	●		lean-ctx init --agent kiro
Antigravity	●		lean-ctx init --agent antigravity
Amazon Q	●		lean-ctx init --agent amazonq
Qwen	●		lean-ctx init --agent qwen
Trae	●		lean-ctx init --agent trae
Verdent	●		lean-ctx init --agent verdent
Aider		●	lean-ctx init --agent aider
Mistral Vibe		●	lean-ctx init --agent vibe
Continue		●	lean-ctx init --agent continue
JetBrains IDEs		●	lean-ctx init --agent jetbrains
QoderWork		●	lean-ctx init --agent qoderwork
VS Code		●	lean-ctx init --agent vscode
Zed		●	lean-ctx init --agent zed
Neovim		●	lean-ctx init --agent neovim
Emacs		●	lean-ctx init --agent emacs
Sublime Text		●	lean-ctx init --agent sublime

Any MCP-compatible client works out of the box — the table above shows agents with first-class auto-setup.

When to use (and when not to)

Great fit if you...

• use AI coding tools daily and your sessions are shell-heavy (git/tests/builds)
• work in medium/large repos (50+ files / monorepos)
• want a local-first layer with no telemetry by default

Skip it if you...

• mostly work in tiny repos and rarely call the shell from your AI tool
• always need raw/unfiltered logs (you can still use --raw, but ROI is lower)

The honest fine print: the payoff depends on three levers — reach (own the window via the proxy/engine, not just the ctx_* tool layer), context lifetime (one long-lived session vs. a fresh process per phase), and provider pricing (prompt-cache-priced vs. re-billed every turn). They stack into a clear win where they line up and net to break-even where they don't. See the win vs. break-even matrix for the full breakdown and how to tune for each case.

Demo

Try these in any repo:

lean-ctx read rust/src/server/mod.rs -m map
lean-ctx -c "git log -n 5 --oneline"
lean-ctx gain --live
lean-ctx dashboard                              # Context Manager (browser)
lean-ctx watch                                  # TUI monitor
lean-ctx benchmark report .

• The repo ships the exact tapes used to render the GIFs in demo/
• Regenerate locally:

vhs demo/leanctx.tape
vhs demo/gain.tape
vhs demo/benchmark.tape

Benchmarks

Real, reproduced numbers — never estimated. Measured on this repo with the GPT-4o tokenizer (o200k_base); a tool that isn't installed is reported as such, never guessed.

Read mode	Compression	Tokens (50 files)	Quality
Raw read	0%	533.2K	100%
map	98.1%	8.0K	78%
signatures	96.7%	14.0K	96%
Cached re-read	~99.99%	~13 tok	100%

lean-ctx's own cost is measured too: the CI-measured fixed per-session footprint (advertised tool schemas + MCP instructions + wakeup briefing) is ~3.0K tokens and gated via lean-ctx doctor overhead --gate. And the long-lived proxy rail has a deterministic self-verify — lean-ctx benchmark dual-arm --json replays a 72-turn session and prices it per model (digest f5ed145e61ce3689, 99.4% input-side saving on cache-priced rails; methodology: bench/agent-task/r2).

Accuracy isn't a vibe: the lossy stages are CI-gated. A model-free A/B gate proves the JSON crusher keeps every gold answer while cutting tokens, and proxy rewrites are byte-stable by contract, so Anthropic (90%) / OpenAI (50%) prompt-cache discounts survive compression. A deterministic off-vs-on testbench (lean-ctx eval testbench) extends the proof to answers: it runs pinned real repos through a raw-dump baseline and through lean-ctx at an identical token budget, grades free-form QA with an LLM judge and code with each repo's own tests, and emits FINDINGS.md (tokens / turns / walltime / quality) plus a regressions file — with a committed recorded subset that blocks CI on any regression.

• Latest snapshot: BENCHMARKS.md
• Reproduce: lean-ctx benchmark report .

By the numbers

• 3,000+ GitHub stars — and counting
• 280+ forks — active community contributions
• 200+ releases — shipped near-daily since launch
• 30+ supported AI coding agents — broadest MCP compatibility
• 83 MCP tools — from simple file reads to multi-agent orchestration
• Used in production by teams running Claude Code, Cursor, and Codex daily
• Live adoption metrics: leanctx.com/metrics — installs, stars and savings, updated continuously

Docs

• Reference (every function, by user journey): docs/reference/ — 11 journeys + CLI/MCP/config appendices
• For AI agents / LLMs: llms.txt — a curated, machine-readable map of lean-ctx (per the llms.txt convention)
• Getting started: https://leanctx.com/docs/getting-started
• Tools reference: https://leanctx.com/docs/tools/
• CLI reference: https://leanctx.com/docs/cli-reference/
• What is LeanCTX: https://leanctx.com/what-is-leanctx/
• Comparison (vs RTK, Context+, MemGPT): https://leanctx.com/compare/
• Pricing & Cloud (local use is free forever): https://leanctx.com/pricing/
• FAQ: discord-faq.md
• Feature catalog (SSOT snapshot): LEANCTX_FEATURE_CATALOG.md
• Monorepo guide: docs/guides/monorepo.md
• Architecture: ARCHITECTURE.md
• Vision: VISION.md

Privacy & security

• No telemetry by default
• Optional anonymous stats sharing (opt-in during setup)
• Disableable update check (config update_check_disabled = true or LEAN_CTX_NO_UPDATE_CHECK=1)
• 40+ security hardening fixes in v3.5.16 (path traversal, injection, CSPRNG, CSP, resource limits — details)
• Context Governance Benchmark self-assessment: graded C2 — Managed against the 32-control CGB v1.0-draft spec, gaps declared — docs/compliance/cgb-self-assessment.md
• Runs locally; your code never leaves your machine unless you explicitly enable cloud sync

See SECURITY.md.

Uninstall

One command removes everything — it stops all processes, then deletes hooks, editor configs, rules, autostart (LaunchAgent/systemd), the data dir, and the binary itself:

lean-ctx uninstall                 # full clean removal
lean-ctx uninstall --dry-run       # preview every change, write nothing
lean-ctx uninstall --keep-config   # keep MCP configs + rules (for reinstall)
lean-ctx-off                       # or just disable for the current shell session

No binary on PATH (or you used the curl installer)? Run the same removal from the installer:

curl -fsSL https://leanctx.com/install.sh | sh -s -- --uninstall

If you installed via a package manager, uninstall removes everything it wrote and tells you the one command to finish removing the binary:

brew uninstall lean-ctx        # Homebrew
cargo uninstall lean-ctx       # cargo install
npm uninstall -g lean-ctx-bin  # npm
pi uninstall npm:pi-lean-ctx   # Pi Coding Agent

Star History

Contributing

Start with CONTRIBUTING.md. Easy first PR: propose a new CLI compression pattern via the issue template.

License

Apache License 2.0 — see LICENSE.

--- lean-ctx: ctx_compose bundles search+read+symbols in one call ---