Muter

Free#19 of 25 in Mutation Testing Tools

Muter: A focused, open-source mutation testing utility for Swift teams using Apple development tools. Ranked #19 of 25 in Mutation Testing Tools by our editors (7.4/10); pricing: Open source; best for swift teams working in Xcode or SPM.

7.4/10Editor score

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At a glance

Editor score
7.4 / 10
Pricing
Open source
Best for
Swift teams working in Xcode or SPM
Paid from
Free
Facts checked
20 Sep 2026

Where it wins
- Supports Xcode projects, workspaces, and Swift Package Manager
- Reports surviving mutants in Xcode's Issue Navigator
- Offers incremental runs, CI workflows, and multiple report formats
Where it doesn't
- Runs on macOS rather than across multiple operating systems
- Supports Swift projects rather than multiple programming languages
- Requires command-line execution for its primary workflow

Our verdict on Muter

Muter is an open-source mutation testing utility for Swift projects on macOS. It modifies source code to create mutants, runs the project's tests, and reports mutation scores for complete test suites and individual files. The tool is aimed at Swift teams working with Xcode projects, Xcode workspaces, or Swift Package Manager projects, including iOS, macOS, tvOS, and watchOS projects that compile and test with xcodebuild.

Its strongest capability is focused feedback on test effectiveness. Muter supports mutation operators including relational operator replacement, side-effect removal, logical connector changes, and ternary swaps. It can run incremental mutation analysis with a files-to-mutate option, helping teams target selected code instead of rerunning every possible mutation. Results are available in plain text, JSON, HTML, and Xcode formats, while configurable test-suite timeouts and coverage thresholds add control for automated workflows. CI support also makes it suitable for incorporating mutation scores into continuous integration processes.

Muter fits teams already centered on Apple's development ecosystem: it integrates with Xcode, places surviving mutants in the Issue Navigator, and supports Xcode test targets and Swift Package Manager tests. Homebrew is also listed as an integration. Its narrow focus is an advantage for Swift-only projects, but it is not suited to teams seeking mutation testing for other languages or operating systems. Choose Muter when Swift test quality, incremental analysis, and Xcode-oriented reporting are priorities; consider another tool when cross-platform execution or broader language coverage is required.

Questions about Muter

What does Muter run on? macOS. It runs self-hosted and as a desktop app.

What does Muter integrate with? 5 integrations: Xcode, Xcode projects, Xcode workspaces, Swift Package Manager and Homebrew.

Who is Muter built for? Solo users, small businesses, mid-market companies and enterprises (our editorial estimate).

Your product? Our editors can test Muter in depth and publish a review, labelled as paid · from $149/mo →

Muter pricing

Plans Open sourceFree Free to use — no paid tier required for the core job.

See plans on github.com

Muter fact sheet

Free plan	Not verified
Paid from	Free
Supported languages	Swift
Test frameworks	Xcode test targets; Swift Package Manager tests
Incremental analysis	Yes
Parallel execution	Not verified
Surviving mutant reports	Yes
Mutation quality gate	Not verified
Mutation operators	RelationalOperatorReplacement; RemoveSideEffects; ChangeLogicalConnector; SwapTernary
Deployment	Self-hosted, Desktop
Platforms	macOS
Support	Community
Built for	Solo, Small business, Mid-market, Enterprise (editorial estimate)
Integrations	5 integrations: Xcode, Xcode projects, Xcode workspaces, Swift Package Manager, Homebrew
Pricing	Open source
Website	github.com
Facts checked	20 Sep 2026

Muter integrations

Muter lists 5 integrations on its own site.

Xcode
Xcode projects
Xcode workspaces
Swift Package Manager
Homebrew

Alternatives to Muter

See all Muter alternatives →

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Featured on iTechGuides

Muter is listed in our Mutation Testing Tools directory. Add the badge to your site — it links back to this page.

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Reviewed by iTechGuides Editors · Editorial team · Updated Nov 2026

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Last updated 14 Nov 2026 · How we research and update