Use JSON Schema to validate request JSON

Use JSON Schema on the backend to validate inbound JSON from client requests. This would provide a relatively easy way to check that request data is in the correct shape and follows basic validation rules (required/optional, data types, max length, etc), without cluttering up the application code with repetitive validations. We will still need to perform some validations of our own, for business logic as well as corners that JSON Schema doesn’t handle, but it gets us a lot in one go.

You can write a schema from scratch without too much trouble, but there are also tools online that can take example JSON output and create a skeleton schema from that. (example generator)

Might also be able to use it to generate per field documentation for each endpoint. (e.g. JSON Schema for Humans)

Start by locating the backend entry points that receive client request JSON and reviewing how request validation is currently handled. Identify the endpoints and request shapes that need schemas, then confirm that required fields, types, and length rules are covered while business-logic validation remains separate.