fast-check
- Android app
- Not listed
- Free plan
- Yes
- Runs on
- api, Linux, Web
Summary
fast-check is a property-based testing library for JavaScript and TypeScript. It generates many inputs, checks specified behavior, and reduces failures to smaller counterexamples that can help pinpoint a problem. Tests are built from arbitraries that create values, properties that express expected behavior, runners that execute checks, and plugins that extend runners. It works with multiple test runners, including Jest, Mocha, Vitest, Ava, Bun, Deno, and the Node.js test runner. You can set seeds, generated value sizes, time limits, and reporting options globally or for an individual assertion. The library also supports stateful testing and reproducible failures, and its project describes fuzzing and generative testing for finding issues such as race conditions and prototype poisoning. It is free and open source under the MIT license. Version 5.x requires Node.js 22.12.0 or later and ECMAScript 2025; TypeScript 5.8 or later is optional.
Who it is for
It suits JavaScript and TypeScript developers who want to check behavior across generated inputs, including stateful scenarios. Its runner-agnostic design can fit projects using a range of test runners.
What is good
- Shrinks failing inputs into smaller counterexamples.
- Works with several popular test runners.
- Supports stateful testing and reproducible failures.
- Runs can be configured with seeds and time limits.
- Free under the MIT license.
What to know first
- Version 5.x requires Node.js 22.12.0 or later.
- Version 5.x requires ECMAScript 2025.
- TypeScript 5.8 or later is optional, not required.
Verdict
fast-check provides a structured way to exercise JavaScript and TypeScript behavior across generated cases, with shrinking to help investigate failures. Check the version 5.x runtime requirements before adopting it.
fast-check plans and pricing
All plansCompared on property-based testing tools
- Free plan
- Yesfast-check.dev
- Supported languages
- JavaScript, TypeScriptfast-check.dev
- Test runner support
- Jest, Mocha, Vitest, Ava, Bun, Deno, Node.js test runnerfast-check.dev
- Failing-case shrinking
- Yesfast-check.dev
- Stateful testing
- Yesfast-check.dev
- Reproducible failures
- Yesfast-check.dev
Facts
- Purpose
- fast-check is a property-based testing library for JavaScript and TypeScript that generates inputs, runs assertions over many cases, and shrinks failures to smaller counterexamples.fast-check.dev · 30 Sept 2026
- Testing workflow
- The library is test-runner agnostic and works with Jest, Mocha, Vitest, and other test runners.fast-check.dev · 30 Sept 2026
- Test building blocks
- Tests use arbitraries to generate values, properties to specify expected behavior, runners to execute properties, and plugins to extend runners.fast-check.dev · 30 Sept 2026
- Configuration
- Users can configure runs, seeds, generated value sizes, time limits, and result reporting globally or per assertion.fast-check.dev · 30 Sept 2026
- Failure diagnosis
- When a property fails, fast-check shrinks the input to a smaller counterexample and reports information that helps diagnose the failure.github.com · 30 Sept 2026
- Additional testing
- The project describes fuzzing and generative testing for finding issues including race conditions and prototype poisoning.fast-check.dev · 30 Sept 2026
- Integrations
- The ecosystem lists official integrations for AVA, Jest, and Vitest, along with connectors for libraries such as Zod and io-ts.fast-check.dev · 30 Sept 2026
- Security testing
- The ecosystem documents an official @fast-check/poisoning package for checking whether specially crafted inputs cause global prototype modifications.fast-check.dev · 30 Sept 2026
- Runtime requirements
- The repository lists fast-check 5.x as requiring Node.js 22.12.0 or later, ECMAScript 2025, and optionally TypeScript 5.8 or later.github.com · 30 Sept 2026
- Open source
- The GitHub repository identifies fast-check as a public project released under the MIT license.github.com · 30 Sept 2026
- Support
- The project invites code and non-code contributions, community help, and financial support through GitHub Sponsors or OpenCollective.fast-check.dev · 30 Sept 2026
- Ecosystem limitations
- The ecosystem page says it can provide stability and maintenance details for official packages, but no specific guarantees for non-official packages.fast-check.dev · 30 Sept 2026
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Sources
- fast-check.dev/docs/introduction/· checked 30 Sept 2026
- fast-check.dev· checked 30 Sept 2026
- fast-check.dev/docs/core-blocks/· checked 30 Sept 2026
- fast-check.dev/docs/configuration/· checked 30 Sept 2026
- github.com/dubzzz/fast-check· checked 30 Sept 2026
- fast-check.dev/docs/ecosystem/· checked 30 Sept 2026
- fast-check.dev/docs/support-us/· checked 30 Sept 2026