JSON Schema basics: validate the shape of JSON

JSON validates syntax (is it parseable). JSON Schema validates structure (does it match what your API expects).

What JSON Schema is for

APIs: ensure requests and responses follow an agreed contract
Forms: validate user input on the client and server
Data pipelines: reject malformed events early

A small example

Example JSON:

{
  "id": 42,
  "email": "[email protected]",
  "role": "admin",
  "active": true
}

Example schema (simplified):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "additionalProperties": false,
  "required": ["id", "email", "role"],
  "properties": {
    "id": { "type": "integer", "minimum": 1 },
    "email": { "type": "string", "format": "email" },
    "role": { "type": "string", "enum": ["admin", "editor", "viewer"] },
    "active": { "type": "boolean" }
  }
}

Key concepts

type: object, array, string, number, integer, boolean, null
required: which keys must exist
additionalProperties: whether unknown keys are allowed
enum: restrict values to a known set
nested validation: schemas can describe nested objects and arrays

How this helps in practice

If you receive “valid JSON but wrong data”, schema validation tells you which field is missing or wrong—much faster than manual debugging.