LeanCTX is a local Rust program that controls the repository context an AI coding agent receives, including selecting, compressing, remembering, and tracking information. Developers use it alongside coding agents to reduce repeated context and manage what those agents read and execute, while the catalogue entries provide related rules, skills, and instructions.
Borrowing it
Nothing to install: this file belongs to yvgude/lean-ctx. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/yvgude/lean-ctx/main/.github/copilot-instructions.mdgit clone --depth 1 https://github.com/yvgude/lean-ctxWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/yvgude/lean-ctx/copilot-instructions)<a href="https://agentmods.dev/instructions/yvgude/lean-ctx/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/yvgude/lean-ctx/copilot-instructions/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/yvgude/lean-ctx/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/yvgude/lean-ctx/copilot-instructions.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00253 | $0.00253 |
| Opus 5.5 | $0.00101 | $0.00101 |
| Sonnet 5.5 | $0.00051 | $0.00051 |
| Haiku 4.5 | $0.00025 | $0.00025 |
Grade A, and why
lean-ctx copilot-instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
lean-ctx shadow mode: native read/search/shell calls auto-route to ctx_* — no tool-mapping needed. File editing → native Edit/StrReplace (lean-ctx only handles reads); if denied, use ctx_patch. Exclusive tools (no native trigger): ctx_compose (understand code, call first), ctx_search(action=symbol) (exact symbol), ctx_search(action=semantic) (by meaning), ctx_callgraph (callers), ctx_knowledge / ctx_session (memory).
OUTPUT STYLE: expert-terse
- Telegraph format: subject-verb-object, drop articles/prepositions
- Symbolic vocabulary: → cause, ∵ because, ∴ therefore, ⊕ add, ⊖ remove, Δ change, ≈ similar, ≠ different, ∈ in/member, ∅ empty/none, ✓ ok, ✗ fail
- Code blocks: untouched (never compress code syntax)
- Each line: max 80 chars
- Zero narration, zero filler
- BUDGET: ≤100 tokens per non-code response
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2mo ago First seen · 17 lines · 253 tokens per session scan A e0b8c6d1b249
lean-ctx copilot-instructions.md is an instructions file published in the GitHub repository yvgude/lean-ctx (3,931 stars, last pushed yesterday), licensed Apache-2.0. It adds 253 tokens to every session, about $0.0010 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
lean-ctx copilot-instructions.md compared with instructions from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| lean-ctx copilot-instructions.mdyvgude/lean-ctx | Instructions file | 3.9k | yesterday | Apache-2.0 | A | 253 | GitHub Copilot |
| vscode buildNext.instructions.mdmicrosoft/vscode | Instructions file | 195k | today | MIT | A | 9,719 | GitHub Copilot |
| next.js AGENTS.mdvercel/next.js | Instructions file | 143k | today | MIT | A | 7,461 | Codex, OpenCode |
| vscode oss-third-party-notices.instructions.mdmicrosoft/vscode | Instructions file | 195k | today | MIT | A | 5,516 | GitHub Copilot |
| langchain AGENTS.mdlangchain-ai/langchain | Instructions file | 149k | today | MIT | A | 4,680 | Codex, OpenCode |
| vscode copilot-instructions.mdmicrosoft/vscode | Instructions file | 195k | today | MIT | A | 3,093 | GitHub Copilot |
| deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness | Instructions file | 274k | 2d ago | MIT | A | 4,313 | Codex, OpenCode |