Csmith

Windows · Linux

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Freedom report

Two barsScore 6.4

Free tierA free tier is on its own pricing page
Open codeNo open-source code on record
Runs widely2 of 6 device platforms
DocumentedPlans, terms and facts published

Csmith is ranked #11 of 27 in fuzz testing software on Freedom251. It runs on Linux, Windows. There is a free plan.

Csmith plans and pricing

All plans

Csmith Free Open-source C program generator github.com · 4 Oct 2026

Compared on fuzz testing software

Free plan: Yes
Input generation methods: generation
Target types: C programs; C++ programs; compilers
Execution mode: local
Supported languages: C; C++
CI/CD support: Yes

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The record

Purpose: Csmith generates random C programs to find compiler bugs using differential testing.
Safe output: Generated C programs are free of undefined behaviors and include per-program statistics.
Other use: The project suggests using Csmith to create a C-program test suite when users do not want to write one themselves.
Compiler workflow: The README demonstrates compiling generated programs with GCC and Clang and comparing their outputs to identify compiler bugs.
Customization: Command-line options shown by `csmith -h` and `csmith -hh` customize random generation.
Execution limit: Generated programs might contain infinite loops, and the README recommends applying timeouts to their execution.
Linux build: The Ubuntu build instructions list g++, CMake, and m4 as prerequisites and use CMake and make to install from source.
Windows build: The project documents building on Windows with Visual Studio or WSL.
Build compatibility: The INSTALL file says Csmith should build on most modern machines with a C++ compiler.
License: The repository includes a COPYING license file.
Support: The project directs users to GitHub issues for bug reports and suggestions and provides a mailing list for discussion.
Support response: The maintainers say they maintain Csmith in their discretionary time and responses to bug reports or feature requests may be delayed.
Origin: Csmith was originally developed at the University of Utah as part of a compiler-testing research project and was open-sourced in 2009.
Price from: Free

Where it ranks on Freedom251

Best Fuzz Testing Software in 2026#11 of 27

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Sources

github.com/csmith-project/csmith· checked 4 Oct 2026
github.com/csmith-project/csmith/blob/master/doc/b· checked 4 Oct 2026
github.com/csmith-project/csmith/blob/master/INSTA· checked 4 Oct 2026
github.com/csmith-project/csmith/blob/master/COPYI· checked 4 Oct 2026