Lean vs Viper
| Lean | Viper | |
|---|---|---|
| Free plan | Yes | No |
| Free trial | No | No |
| Paid from | Free | — |
| Open source | No | No |
| Platforms | Linux, macOS, Web, Windows | extension, Linux, macOS, Web, Windows |
| Verification method | deductive | hybrid |
| Supported formalisms | theorem-proving | contracts |
| Proof artifacts | Yes | — |
| Input languages | Lean 4 | Viper language; Go, Python, and Rust via front-end tools |
| Deployment | both | self-hosted |
| Free plan | — | Yes |
| Counterexamples | — | Yes |
Both are listed in Best Formal Verification Tools. On Specifiction, Lean scores higher on our published basis.