lean SKILL.md skillB
lean from swingerman/engineer is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add swingerman/engineer/lean@git:20261020.a98004ePins git:20261020.a98004e in mdr.lock. Pin the fingerprint instead.
- Audit grade
- B, 16 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- swingerman/engineer
- Path
engineer/skills/lean/SKILL.md- Versions recorded
- 3
- Latest version
- git:20261020.a98004e, committed Oct 20, 2026
- First version recorded
- Sep 23, 2026
- Size
- 6,564 bytes
- Repository stars
- 157
- License
- MIT
Use to formally verify real code with Lean 4. Model a function or state machine as written, prove an invariant for every input, and reproduce any counterexample as a failing test. Dispatched by /engineer.harden for all-inputs invariants (parsers, maskers, money math, permission predicates); also usable directly. Triggers — "/engineer.lean", "use lean to verify X", "prove X can't happen", "lean-verify this code".
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Lean Lean is only useful here if the proof actually compiles. Don't hand back `sorry`-riddled code and call it done — the whole point of a proof assistant is that `lake build` is the ground truth, not your judgment about whether the proof "looks right." ## Setup check First run: ```bash which lean lake elan ``` If missing, tell the user and offer to install via elan (the Lean toolchain manager) — don't install it silently, it's a real download: ```bash curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh ``` If the project has a `lakefile.lean`/`lakefile.toml` + `lean-toolchain`, just `cd` into it and use `lake build` — don't reinvent the toolchain setup. ## Workflow 1. **Write/edit the `.lean` file.** 2. **Check it**: `lake build` (whole project) or `lake env lean file.lean` (single file, faster while iterating). 3. **Read the error precisely.** Lean errors point at the exact tactic state — the "unsolved goals" block tells you exactly what's left to prove. Don't guess; read the goal state and pick a tactic that closes it. 4. **Before writing a new proof from scratch, check if Mathlib already has …
Read the whole file at its exact version.
How to install
mdr add swingerman/engineer/lean@sha256:a52f5e3260aa14b4The line at the top of this page pins the label git:20261020.a98004e, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_xp6jse42isi2zf6l)
3 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 3 versions of this file, between Sep 23, 2026 and Oct 20, 2026, about one every 13 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20261020.a98004e latest | 2026-10-20 | a98004e | 6,564 B | B | view · diff |
| git:20260923.5520e1e | 2026-09-23 | 5520e1e | 6,334 B | B | view · diff |
| git:20260923.37de0f0 | 2026-09-23 | 37de0f0 | 6,582 B | B | view |
Audit of the latest version
- fail: No curl or wget piped into a shell (matched: curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh)
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (6564 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Starting a new one? Use a template for SKILL.md on mdpantry, which passes every one of these checks and says what to change in it.
Source
swingerman/engineer · 157 stars · license MIT · pushed 2026-10-20 · branch master
API
GET https://markdownregistry.com/api/v1/artifacts/art_xp6jse42isi2zf6l GET https://markdownregistry.com/api/v1/resolve?ref=swingerman/engineer/lean GET https://markdownregistry.com/api/v1/blob/a52f5e3260aa14b4d3ba6fa05c6a4f37c285098ec971267a8907a03f8e4f4d31
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.
More from swingerman/engineer
Every file in swingerman/engineer