Side by side
F* vs Isabelle
Both stand on formal verification tools. Which one you can start free with, which one lets you read the code, and what each costs once you pay.
Free plan LinuxMacSelf-hosted+1
Pick F* if your work calls for a proof-oriented language with both automated and interactive theorem proving, or for code that can be extracted to several targets. Consider whether its proof-focused approach fits your project and whether you want to install binaries, use a package-based route, or build from source.
Visit F* Free plan LinuxMacSelf-hosted+1
Isabelle combines formal proof development with tools for verification and code generation. Its proof environments are available across several platforms, though first launch on Windows and macOS requires addressing their rejection of unsigned applications.
Visit IsabelleThe facts
| F* | Isabelle | |
|---|---|---|
| Free plan | Yes | Yes |
| Open source | Not published | Not published |
| Runs on | Linux, Mac, Self-hosted, Windows | Linux, Mac, Self-hosted, Windows |
| Lowest paid plan | Free or on request | Free or on request |
| Plans published | 1 | 1 |
| Maker | Not published | Not published |
| Website | fstar-lang.org | isabelle.in.tum.de |
| On formal verification tools | #6 of 34 | #10 of 34 |
F*: what it does well
- Free and open source under Apache 2.0.
- Combines dependent types with SMT and tactic-based proof.
- Compiles to OCaml by default.
- Supports extraction to F#, C, WebAssembly, or assembly.
- Offers binaries and several installation routes.
What to know first
- The language is focused on proof-oriented programming.
- Some output targets require KaRaMeL or Vale.
- Installation from source is an available route.
Isabelle: what it does well
- Free distribution with open-source licenses
- Includes a theory library of verified mathematics
- Generates code in four listed languages
- Provides real-time proof checking in Isabelle/jEdit
What to know first
- Windows rejects the app by default at first run
- macOS requires users to allow the unsigned app