ajv-validator/ajv

Ajv is a JSON validator for Node.js and the browser. Its job is simple to describe: you hand it a schema (a set of rules about what a JSON document should look like) and some data, and Ajv tells you whether the data matches the rules. The README calls it the fastest JSON validator and notes that more than 100 people have contributed to it over the years. A schema is just a description of the expected shape of data, such as which fields are required, what types they should be, and what values are allowed. Ajv supports several versions of the JSON Schema standard, specifically drafts 04, 06, 07, 2019-09, and 2020-12. Support for the older draft-04 needs an extra package called ajv-draft-04. It also supports JSON Type Definition, a newer alternative format defined in RFC 8927. The project's website explains the difference between the two languages so users can pick the right one for their case. The README itself is mostly a landing page. It points to the documentation site at ajv.js.org, which holds a getting started guide, an API reference, notes on strict mode, instructions for generating standalone validation code, security considerations, a command line interface called ajv-cli, and a frequently asked questions page. Most users will spend their time on the documentation site rather than in this repository. The project is sponsored by organisations including Mozilla, Microsoft, Retool, Tidelift, and SimpleX, and it has received a MOSS grant. The author asks for sponsorship through GitHub Sponsors or Open Collective to keep development going, especially around the next major version. There is also a contributing guide for people who want to help with code or documentation. For a non-technical reader, the main thing to take away is that Ajv is plumbing. Other tools and libraries use it under the hood to check that JSON data, often from APIs or configuration files, follows agreed-on rules before they try to use it.