How to Validate JSON Against a JSON Schema

Syntax validation is not schema validation

A JSON document can be syntactically valid but still violate an application contract. Schema validation checks expected types, required properties, patterns and other constraints.

Read validation errors by path

Each error should identify the failing instance path and the violated schema keyword. Fix the first structural errors before interpreting dependent errors lower in the document.

Common schema rules

Use only constraints that represent real business or interface requirements.

• type controls the expected JSON type.
• required lists mandatory object properties.
• properties defines rules for named fields.
• items defines array element rules.
• minimum, pattern and enum narrow accepted values.

Test both passing and failing examples

A useful contract test includes valid samples and deliberate failures for missing fields, wrong types, invalid enum values and boundary conditions.