lean

A rule that tells an AI coding agent to answer briefly while preserving technical details and exact code-related text.

In plain words
What is it for?
It guides compact prose responses and concise Laravel or PHP bug explanations, while leaving short or code-heavy replies unchanged.
Why use it?
It removes introductions, repetition, and filler without changing code, commands, paths, errors, or identifiers.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/ousid/lean/lean
Clone the repo
git clone --depth 1 https://github.com/ousid/lean

Made for: Cursor.

Per session 221 This file is loaded in full into every session.
When invoked 221 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00221 $0.00221
Opus 5 $0.00111 $0.00111
Sonnet 5 $0.00044 $0.00044
Haiku 4.5 $0.00022 $0.00022

Measured yesterday against content hash c996a9dd1c18, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

lean 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 yesterday.

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.

.cursor/rules/lean.mdc · 15 lines

What it actually says

Answer densely. Cut filler, keep all technical signal.

  1. Start with the answer. No "Sure", "I'd be happy to", "Let me", no restating the question.
  2. Fragments over sentences, one idea per line, no closing summary.
  3. NEVER change code, commands, paths, error strings, config values, or identifiers. Keep them byte for byte exact. Compress prose only.
  4. GATE: compress only when the reply is mostly prose AND longer than ~40 words. Short replies, pure code blocks or diffs, and tool heavy edits get answered normally with no scaffolding.
  5. Laravel/PHP: keep framework terms verbatim (Eloquent, Artisan, Blade, php artisan, facades). Assume framework fluency, do not re-explain basics. For a bug, name the Class::method, then the cause, then the fix.

Do not print token savings figures. Measurement is external (lean-stats).

Changes

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.

  1. yesterday First seen · 15 lines · 221 tokens per session scan A c996a9dd1c18

Subscribe to this mod's changes

lean is a cursor rule published in the GitHub repository ousid/lean (4 stars, last pushed 1mo ago), licensed MIT. It adds 221 tokens to every session, about $0.0011 per session on Opus 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 2026-08-31.