Welcoming Repositories Index Lean Ecosystem
Top Welcoming Open-Source Lean Repositories
Top welcoming Lean repositories. Scored by real 90-day external PR merge rates, maintainer review turnaround speed, and first-time contributor success.
Updated daily • Sun, 30 Aug 2026 UTC
Tracked Repos
38
>100 stars verified
Avg Merge Rate
35%
90-day external PRs
Open GFIs
42
Beginner friendly issues
Welcoming Tier
12
S & A Tier maintainers
Ranked Lean Repositories
Showing top 38 of 38 ranked repositories
| Rank | Repository | Tier | Score | Merge Rate | Good First Issues |
|---|---|---|---|---|---|
| #1 | Catalog Of Math Problems Formalized In Lean | S•Elite | 72.9 | 90.3% | - |
| #2 | S•Elite | 70.7 | 83.3% | - | |
| #3 | Formally verified smart contracts gives mathematical certainty across all inputs and execution paths. We bet that agents will make full formal verification practical. | B•Solid | 69.6 | 97.8% | - |
| #4 | Formalization of Mathematical Logic | A•Welcoming | 66.5 | 78.3% | - |
| #5 | The "batteries included" extended library for the Lean programming language and theorem prover | A•Welcoming | 64.8 | 65.0% | - |
| #6 | Lean documentation authoring tool | A•Welcoming | 62.9 | 64.9% | - |
| #7 | Definitional implementation of Cedar language and utilities for DRT | A•Welcoming | 62.1 | 73.3% | - |
| #8 | Ongoing Lean formalisation of the proof of Fermat's Last Theorem | A•Welcoming | 61.0 | 70.4% | - |
| #9 | The Lean reference manual | A•Welcoming | 59.4 | 82.6% | - |
| #10 | An AIs-welcome Lean library downstream of Mathlib: AI handle the implementation and review, humans write the roadmaps and review rubrics | A•Welcoming | 57.8 | 15.2% | 4 |
| #11 | Formally Verified Arguments of Knowledge in Lean | A•Welcoming | 57.3 | 64.7% | - |
| #12 | A formalized proof of Carleson's theorem in Lean | A•Welcoming | 56.1 | 81.8% | - |
| #13 | The Lean Computer Science Library (CSLib) | A•Welcoming | 55.2 | 44.4% | - |
| #14 | Lean 4 port of Iris, a higher-order concurrent separation logic framework | B•Solid | 55.0 | 75.4% | - |
| #15 | thomasahle/sunfish3,270 Sunfish: a Python Chess Engine in 111 lines of code | B•Solid | 54.6 | 65.4% | - |
| #16 | A type-safe, formally verifiable HDL compiler in Lean 4. Inspired by Clash, built for high-assurance hardware synthesis. | B•Solid | 54.3 | 72.7% | - |
| #17 | Wasm interpreter in lean, designed for reasoning | B•Solid | 53.4 | 43.5% | - |
| #18 | A project to digitalise results from physics into Lean. | B•Solid | 49.1 | 12.5% | 38 |
| #19 | leanprover/lean48,931 Lean 4 programming language and theorem prover | B•Solid | 48.8 | 8.3% | - |
| #20 | A collection of formalized statements of conjectures in Lean. | B•Solid | 48.4 | 58.5% | - |
| #21 | A Lean library for machine-checked cryptographic proofs. | B•Solid | 48.0 | 7.1% | - |
| #22 | teorth/analysis1,872 A Lean companion to Analysis I | B•Solid | 47.8 | 72.1% | - |
| #23 | The math library of Lean 4 | D•Risky | 23.3 | 0.0% | - |
| #24 | A verifier for automated and interactive proofs about transition systems. | D•Risky | 17.3 | 0.0% | - |
| #25 | Source code for the Mathematics in Lean tutorial. | D•Risky | 8.0 | 0.0% | - |
| #26 | D•Risky | 0.0 | 0.0% | - | |
| #27 | digama0/mm0412 Metamath Zero specification language | D•Risky | 0.0 | 0.0% | - |
| #28 | White-box automation for Lean 4 | D•Risky | 0.0 | 0.0% | - |
| #29 | Natural Number Game | D•Risky | 0.0 | 0.0% | - |
| #30 | Blueprint for the PNT+ Project | D•Risky | 0.0 | 0.0% | - |
| #31 | Tactics for discharging Lean goals into SMT solvers. | D•Risky | 0.0 | 0.0% | - |
| #32 | ATLAS Autoformalized Textbook Library At Scale | D•Risky | 0.0 | 0.0% | - |
| #33 | An evaluation benchmark for undergraduate competition math in Lean4, Isabelle, Coq, and natural language. | D•Risky | 0.0 | 0.0% | - |
| #34 | D•Risky | 0.0 | 0.0% | - | |
| #35 | Helper toolkit for creating your own Lean 4 UserWidgets | D•Risky | 0.0 | 0.0% | - |
| #36 | D•Risky | 0.0 | 0.0% | - | |
| #37 | D•Risky | 0.0 | 0.0% | - | |
| #38 | A blueprint for a formalization of infinity-cosmos theory in Lean. | D•Risky | 0.0 | 0.0% | - |
How to Get Your Lean PR Merged
1
Check C-Rankâ„¢ First: Pick projects with S or A tiers to avoid maintainer ghosts and slow review cycles.
2
Run Local Verification: Ensure test suites and formatting linters pass before opening a pull request.
3
Submit in Maintainer Windows: Check the repository report card to submit when maintainers are most active.
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Frequently Asked Questions: Lean Open Source
What is the most welcoming Lean open-source repository?
The highest-ranked Lean repository on GetMerged is currently dwrensha/compfiles, with a C-Rank score of 72.9/100 and a 90.3% PR merge rate.
How can I find good first issues in Lean?
You can browse verified beginner-friendly issues in Lean by visiting our curated Good First Issues directory at getmerged.abhishekco.de/good-first-issue/lean.
What makes a Lean repository ‘Super Welcoming’ on GetMerged?
A ‘Super Welcoming’ (S-Tier) Lean repository demonstrates an external PR merge rate above 80%, a median first response time within 24 to 48 hours, active review feedback, and clear onboarding documentation.