JSON SCHEMA
JSON DATA
VALIDATION RESULTS
Validation results appear here
Paste schema + data then click Validate// validate JSON data against a JSON Schema definition
Validate JSON data against a JSON Schema definition. Supports Draft-07 keywords: type, required, properties, enum, format, minimum, pattern, allOf, anyOf, oneOf, not. Free, no sign-up.
Validation results appear here
Paste schema + data then click Validatetype | Value type: "string", "number", "integer", "boolean", "object", "array", "null" |
enum | Value must be one of the listed values |
const | Value must exactly equal this constant |
minLength | Minimum string length |
maxLength | Maximum string length |
pattern | String must match regex pattern |
format | Semantic format: email, date, uri, uuid… |
minimum | Minimum value (inclusive) |
maximum | Maximum value (inclusive) |
exclusiveMinimum | Minimum value (exclusive) |
exclusiveMaximum | Maximum value (exclusive) |
multipleOf | Must be a multiple of this number |
required | Array of required property names |
properties | Schema for each property |
additionalProperties | false to disallow unknown properties |
minProperties | Minimum number of properties |
maxProperties | Maximum number of properties |
items | Schema that each array element must match |
minItems | Minimum number of items |
maxItems | Maximum number of items |
uniqueItems | true — all items must be unique |
allOf | Must be valid against ALL schemas in array |
anyOf | Must be valid against AT LEAST ONE schema |
oneOf | Must be valid against EXACTLY ONE schema |
not | Must NOT be valid against the schema |
if / then / else | Conditional schema application |
Click a template button to load a ready-made schema, or paste your own JSON Schema in the left panel. Use the sample data that loads with the template or paste your own JSON data.
The validator checks every constraint in the schema against the data and reports each violation with the exact path and a clear error message.
Fix the data or schema based on the error messages and validate again. Changes update automatically with the live validate option.
JSON Schema Validator checks whether JSON data conforms to a JSON Schema definition. It implements the JSON Schema Draft-07 specification including type checking, required fields, property schemas, string/number/array constraints, format validation, and composition keywords — entirely in your browser, free, with no data sent anywhere.
JSON Schema is a declarative language for describing the structure and validation rules of JSON data. A JSON Schema document is itself a JSON object that specifies what values are valid — their types, required fields, string patterns, numeric ranges, and more. JSON Schema is widely used to document APIs (OpenAPI uses it), validate configuration files, generate forms, and enforce data contracts between services. The current widely supported draft is Draft-07, though Draft 2019-09 and 2020-12 also exist.
allOf requires the data to be valid against every schema in the array — it is a logical AND. anyOf requires the data to be valid against at least one schema in the array — a logical OR that allows multiple schemas to match. oneOf requires the data to be valid against exactly one schema — a logical exclusive OR. If zero or more than one schema in a oneOf matches, validation fails. oneOf is commonly used to define mutually exclusive variants of a type.
The format keyword is validated against these standard formats: email (basic email pattern), date (YYYY-MM-DD), time (HH:MM:SS), date-time (ISO 8601), uri (URL pattern), uuid (UUID v4 pattern), ipv4 (IPv4 address), ipv6 (IPv6 address), and hostname. The JSON Schema specification defines format as advisory by default, but this tool validates all listed formats as hard constraints.
By default, JSON Schema allows an object to have any properties beyond those listed in properties. Setting additionalProperties: false makes the schema strict — only the properties explicitly listed in properties (and patternProperties) are allowed. Any extra key in the data produces a validation error. This is useful for catching typos in property names and for enforcing strict API contracts where unexpected fields should be rejected.
required is a list of property names that must be present in the object — it controls which keys are mandatory. properties defines the schema that each named property must conform to, but does not make any property required by itself. A property can be in properties but not in required (it is optional but validated if present), or in required but not in properties (it must be present but can be any value).
This tool implements JSON Schema Draft-07, which is the most widely supported version and the one used by the majority of tools and libraries. Draft-07 introduced if/then/else conditional schemas and the readOnly/writeOnly keywords. It is the version used by VS Code's JSON language server, OpenAPI 3.0, and most popular validation libraries. Draft 2019-09 and 2020-12 are newer but less universally supported.
JSON Schema has become the standard way to define the expected structure of JSON data — what fields are required, what types each field must have, what ranges and patterns are acceptable, and what combinations of values are valid. Validating JSON against a schema is an essential step in API development, data pipeline construction, and configuration management. This validator implements the JSON Schema Draft-07 specification and checks every constraint defined in the schema.
The type keyword is the most fundamental constraint. JSON Schema distinguishes seven types: string, number, integer (a number with no fractional part), boolean, object, array, and null. Types can be specified as a single string or as an array to allow multiple types. The validator checks the actual JavaScript type of each value against the schema's type constraint and reports mismatches with the exact path to the failing value.
The required array lists which properties must be present in an object. If any required property is missing from the data, validation fails with a clear message identifying the missing key and its location in the document. The properties object maps each property name to a schema that the property's value must satisfy — enabling recursive validation of deeply nested structures.
JSON Schema's composition keywords — allOf, anyOf, oneOf, and not — enable complex validation logic. They allow schema authors to express unions of types, discriminated unions, and negations. The if/then/else keywords (introduced in Draft-07) enable conditional validation: if a value matches the if schema, it must also match the then schema; otherwise it must match the else schema. This is used for polymorphic validation where different sets of rules apply depending on the value of a discriminator field.