Ajv vs Yup
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A fast library that checks whether JSON data matches a schema, for Node.js and browsers.
Open source · MIT
A JavaScript/TypeScript library for defining schemas that validate and convert data at runtime.
The short answer
Choose Ajv if you need…
- Node.js developers validating API request or response bodies
- Front-end developers validating form or config data in the browser
- Teams already writing JSON Schema who need a standards-based checker
- Projects that need draft-04 support (via the separate ajv-draft-04 package)
Choose Yup if you need…
- Developers validating form or API input in JavaScript or TypeScript
- Teams that want TypeScript types inferred from a validation schema
- Projects that need async validation, such as checking against a server
- Developers who want to extend schemas with their own custom methods
Side-by-side
| Ajv | Yup | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 14.9k | 23.7k |
| Setup difficulty | Intermediate | Beginner |
| How you get it | Install with a package manager | Install with a package manager |
| Main language | TypeScript | TypeScript |
| Last code update | 2 months ago | 7 days ago |
What each one is
Ajv
Ajv is a JavaScript/TypeScript library that checks JSON data against a schema, such as confirming a form submission or API request has the required fields and types. It supports JSON Schema drafts 04, 06, 07, 2019-09 and 2020-12, plus JSON Type Definition (RFC 8927). The README describes it as fast, and it generates validation code from schemas to achieve this.
Yup
Yup lets you describe the expected shape of a value, such as a user object with a name, age, and email, using chained method calls. You can then check incoming data against that schema, or convert ('cast') it into the correct types. It is commonly used to check form input or API data before using it.
Best for
Ajv
- Node.js developers validating API request or response bodies
- Front-end developers validating form or config data in the browser
- Teams already writing JSON Schema who need a standards-based checker
- Projects that need draft-04 support (via the separate ajv-draft-04 package)
Yup
- Developers validating form or API input in JavaScript or TypeScript
- Teams that want TypeScript types inferred from a validation schema
- Projects that need async validation, such as checking against a server
- Developers who want to extend schemas with their own custom methods
Strengths
Ajv
- The README claims it is the fastest JSON schema validator and cites third-party benchmarks
- Supports multiple JSON Schema drafts and JSON Type Definition
- MIT licensed with a large community (over 100 contributors per the README)
Yup
- Concise chained syntax that the README describes as expressive enough for complex, interdependent validations
- Strong TypeScript support, including inferring static types from schemas
- Clear error details and support for custom error messages and localization
Not ideal for
Ajv
- People who are new to programming and just want a simple form library, since it requires writing schemas
- Projects that need a non-JavaScript runtime, since the README only mentions Node.js and browsers
- Users who only need to check a few values by hand, where a simple function would be enough
Yup
- Projects that do not use JavaScript or TypeScript, since the library is written for that ecosystem
- Users who need a non-developer tool with a visual interface
- Projects on the pre-v1 API, since the README points to a separate pre-v1 branch for those docs
Trade-offs
Ajv
- Draft-04 support requires an extra package, so setup is not one step for older schemas
- The README is short and points to an external website for most documentation
- Performance claims come from the project's own README citing older benchmarks
Yup
- The README is truncated, so this summary covers only the first part of the API reference
- Its full feature set and edge cases are documented elsewhere and were not visible here
- Pre-v1 users must use a different documentation branch
Getting started
Frequently asked questions
What is the difference between Ajv and Yup?
Ajv: A fast library that checks whether JSON data matches a schema, for Node.js and browsers. Yup: A JavaScript/TypeScript library for defining schemas that validate and convert data at runtime. Ajv suits node.js developers validating api request or response bodies, while Yup suits developers validating form or api input in javascript or typescript.
Are Ajv and Yup free?
Ajv: Free and open source. Yup: Free and open source.
Which is easier to set up, Ajv or Yup?
Yup is easier to get started with (rated beginner); Ajv is rated intermediate and usually needs more setup.
Is Ajv or Yup more popular?
Yup has more GitHub stars (23.7k) than Ajv (14.9k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to Ajv and Yup?
Other options people compare them with include Zod, Formily, Pydantic, SQLModel.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.