Mutant

Input—per 1M tokens

Output—per 1M tokens

Context—tokens

WeightsClosed

About

Mutant is ranked #4 of 25 in mutation testing tools on Inferse. It runs on Linux, macOS. There is a free plan. Paid plans start at $20.83/mo.

Compared on mutation testing tools

Free plan: Yesgithub.com
Paid from: $30/mogithub.com
Supported languages: Rubygithub.com
Test frameworks: RSpec, Minitest, Test::Unitgithub.com
Incremental analysis: Yesgithub.com
Parallel execution: Yesgithub.com
Surviving mutant reports: Yesgithub.com
Mutation operators: Arithmetic, logical, bitwise, statement removal, return-value modification, orderinggithub.com

Facts

Purpose: Mutant is mutation testing for Ruby that systematically modifies code and verifies that tests catch each change.github.com · 1 Oct 2026
Mutation operators: Mutant mutates arithmetic, logical and bitwise operators, removes statements, and modifies return values.github.com · 1 Oct 2026
Test integrations: Mutant integrates with RSpec, Minitest, and Test::Unit.github.com · 1 Oct 2026
CI workflow: Mutant supports incremental mode for running mutation testing in CI.github.com · 1 Oct 2026
Ruby support: Mutant supports Ruby versions 3.2, 3.3, 3.4, and 4.0 for runtime, syntax, and mutations.github.com · 1 Oct 2026
Rails integration: Mutant supports Rails applications with parallel-worker database isolation for PostgreSQL and SQLite.github.com · 1 Oct 2026
Rails versions: The Rails integration is verified for Rails 7.2, 8.0, and 8.1.github.com · 1 Oct 2026
Subject limitation: Mutant cannot emit mutations for methods defined within closures such as module_eval, class_eval, define_method, or define_singleton_method.github.com · 1 Oct 2026
Execution model: Mutant runs exclusively on developers’ machines or in CI.github.com · 1 Oct 2026
Source-code privacy: Schirp DSO LTD states that it does not get access to customers’ source code, customer data, or other sensitive material.github.com · 1 Oct 2026
Data sharing: Customer information is never shared or sold to anyone.github.com · 1 Oct 2026
Support channels: Mutant provides Discord, GitHub Issues, and release announcements as communication channels.github.com · 1 Oct 2026
Commercial licensing: Commercial subscriptions are required per developer using Mutant on commercial code, while CI execution requires no additional subscriptions.github.com · 1 Oct 2026
Creator: Mutant was created and is developed by Markus Schirp and is cited as subject of IEEE-published research.github.com · 1 Oct 2026