What is json-schema?

This is a PHP library for validating JSON data against a JSON Schema. JSON Schema is a standard way to describe the expected shape and content of a JSON document, similar to a contract that says "this field must be a number, that field must be a string no longer than 50 characters." The library checks whether a given piece of JSON actually follows the rules defined in a schema file, and reports any violations. The library supports schema drafts 3, 4, 6, and 7, which are successive versions of the JSON Schema specification. Newer draft versions may have features that are not yet implemented. Installation is done through Composer, the standard PHP package manager: one command adds it to your project. Basic usage involves loading your JSON data, pointing the validator at a schema file, calling validate, and then checking whether the result passed or reading back a list of error messages with the field name and the reason each check failed. Beyond basic checking, the library offers a few optional behaviors you can switch on. Type coercion lets the validator automatically convert a string like "17" to the number 17 if the schema expects a number, which is useful when handling data sent over HTTP where everything arrives as a string. A default values mode automatically fills in missing fields using the default values defined in the schema. There is also a mode that throws a PHP exception immediately on the first validation failure rather than collecting all errors. Schemas can reference other schemas using a standard reference syntax, and the library includes a storage class that resolves those references by loading additional schema files as needed. A flag table in the README lists all available validation modes and what each one does.