JSON Schema Fundamentals: Validate, Document & Enforce Data Contracts
2026-04-24 8 min read
JSON Schema is a declarative language for describing the structure and constraints of JSON documents. It answers questions like: "Is this JSON valid? Does it have all required fields? Are the values in the right format?"
Core Schema Concepts
Type Constraint
Basic type validation
{
"type": "object",
"properties": {
"name": { "type": "string" },
"age": { "type": "integer" },
"active": { "type": "boolean" }
}
}Required Fields
Enforcing required fields
{
"type": "object",
"properties": {
"email": { "type": "string" },
"password": { "type": "string" }
},
"required": ["email", "password"]
}Constraints (Format, Length, Range)
Advanced constraints
{
"type": "object",
"properties": {
"email": { "type": "string", "format": "email" },
"age": { "type": "integer", "minimum": 0, "maximum": 150 },
"username": { "type": "string", "minLength": 3, "maxLength": 20 }
}
}Real-World Use Cases
- API documentation and contract testing
- Form validation on both client and server
- Configuration file validation
- Database record validation
- Message queue payload validation
Generate from examples
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