Dafny vs Lean
Dafny
dafny.org
Lean
lean-lang.orgSide by side
| Figure | Dafny | Lean |
|---|---|---|
| Price from | — | Free |
| Free plan | — | Yes |
| Free trial | — | — |
| Open source | — | — |
| Web | — | Yes |
| Windows | Yes | Yes |
| macOS | Yes | Yes |
| Linux | Yes | Yes |
| Self-hosted | Yes | — |
| Plans published | 0 | 1 |
| Spec score · Formal Verification Tools | 7.8 (#16) | 8.6 (#2) |
| Learning resources | The Dafny documentation links to a getting-started tutorial, reference manual, FAQs, error explanations, verification optimization guide, style guide, and examples. | The learning page links to textbooks, tutorials, interactive games, core documentation, and an API reference. |
| License | The Dafny software is licensed under the MIT License. | Lean is released under the Apache 2.0 license, which the documentation describes as allowing others to use and extend the code and mathematical libraries freely. |
| Platforms | Installation instructions cover Windows, Linux, and macOS; the project repository also lists binary downloads for FreeBSD. | The reference lists Linux, macOS, and Windows among Lean’s supported platforms, with Tier 1 binary releases available through elan. |
| Support | The project homepage directs users to a Zulip channel to ask questions about Dafny. | The Lean Community Zulip is described as the central hub for questions and collaboration, and Lean FRO hosts weekly technical office hours. |
| What it does | Dafny is a verification-aware programming language with native support for recording specifications and a static program verifier that checks code against them. | Lean is an open-source programming language and proof assistant for writing correct, maintainable, formally verified code. |
Plans
In their own words
Lean
Lean is an open-source programming language and proof assistant for formalizing mathematics, verifying software, and writing general code. Its minimal trusted kernel checks proofs, and the project describes it as supporting correctness in mathematical, software, and hardware verification. Lean includes the Grind tool for automating some pattern matching, case analysis, and systems of linear inequalities; metaprogramming lets users add notation and proof automation. Projects are managed with Lake, the package manager bundled with Lean. Mathlib is a community-driven library with over a million lines spanning areas including algebra, analysis, topology, probability, and computer science. The recommended setup uses VS Code with the Lean 4 extension for syntax highlighting and code completion, while Neovim with lean.nvim is also well-supported. Lean runs on Linux, macOS, and Windows, and Lean4Web lets users run code in a browser. The software is free under the Apache 2.0 license. Learning resources include textbooks, tutorials, interactive games, documentation, and an API reference.