How do I validate JSON against a schema?

Paste your JSON Schema on the left, the data you want to check on the right. Specway uses Ajv (the most popular JSON Schema validator on npm) to compile the schema and run validation. Errors include the field path and a precise message. Pure browser — no upload.

What's JSON Schema vs OpenAPI schema?

JSON Schema is the underlying standard for describing JSON shapes. OpenAPI 3.0 used a JSON Schema dialect with some differences; OpenAPI 3.1 fully aligned with JSON Schema 2020-12. Schemas in your OpenAPI components/schemas section ARE JSON Schema — you can validate API request/response bodies with this tool.

Which JSON Schema drafts are supported?

Ajv supports drafts 04, 06, 07, 2019-09, and 2020-12 (the current standard). For OpenAPI 3.0 schemas, draft-04 quirks apply (no const, exclusiveMaximum is boolean, etc). For OpenAPI 3.1, use 2020-12 features. The validator auto-detects from the schema's $schema URL.

How do I validate a request body against my OpenAPI spec?

Extract the schema from your OpenAPI spec at components.schemas.YourType, paste it as the schema, and paste the request body as the data. For full request validation including parameters, headers, and content-type, use a request-validation library or middleware (express-openapi-validator, fastify-openapi-glue, etc.) at runtime.

What does \"strict mode\" mean?

Ajv's strict mode rejects schemas that use ambiguous syntax (unknown keywords, conflicting types). The web tool runs in non-strict mode for compatibility — pasting an OpenAPI 3.0 schema with vendor extensions just works. For production, use strict mode and clean your schemas.

Why does my data fail validation but my API accepts it?

Three common reasons: (1) the API does looser validation than its declared schema. (2) your schema is wrong — the API accepts what works, not what's documented. (3) the API has middleware that coerces types (numeric strings to ints, for example). Run validation in CI to catch schema drift before customers hit it.

Can I validate huge JSON documents?

Ajv compiles the schema once, then validates any data size in O(n). Browser memory is the bottleneck. For multi-megabyte files, expect smooth validation but slow textarea editing. For gigabyte-scale data, validate in Node with the ajv CLI instead.

How do I validate JSON against a schema?

Paste your JSON Schema on the left, the data you want to check on the right. Specway uses Ajv (the most popular JSON Schema validator on npm) to compile the schema and run validation. Errors include the field path and a precise message. Pure browser — no upload.

What's JSON Schema vs OpenAPI schema?

JSON Schema is the underlying standard for describing JSON shapes. OpenAPI 3.0 used a JSON Schema dialect with some differences; OpenAPI 3.1 fully aligned with JSON Schema 2020-12. Schemas in your OpenAPI components/schemas section ARE JSON Schema — you can validate API request/response bodies with this tool.

Which JSON Schema drafts are supported?

Ajv supports drafts 04, 06, 07, 2019-09, and 2020-12 (the current standard). For OpenAPI 3.0 schemas, draft-04 quirks apply (no const, exclusiveMaximum is boolean, etc). For OpenAPI 3.1, use 2020-12 features. The validator auto-detects from the schema's $schema URL.

How do I validate a request body against my OpenAPI spec?

Extract the schema from your OpenAPI spec at components.schemas.YourType, paste it as the schema, and paste the request body as the data. For full request validation including parameters, headers, and content-type, use a request-validation library or middleware (express-openapi-validator, fastify-openapi-glue, etc.) at runtime.

What does \"strict mode\" mean?

Ajv's strict mode rejects schemas that use ambiguous syntax (unknown keywords, conflicting types). The web tool runs in non-strict mode for compatibility — pasting an OpenAPI 3.0 schema with vendor extensions just works. For production, use strict mode and clean your schemas.

Why does my data fail validation but my API accepts it?

Three common reasons: (1) the API does looser validation than its declared schema. (2) your schema is wrong — the API accepts what works, not what's documented. (3) the API has middleware that coerces types (numeric strings to ints, for example). Run validation in CI to catch schema drift before customers hit it.

Can I validate huge JSON documents?

Ajv compiles the schema once, then validates any data size in O(n). Browser memory is the bottleneck. For multi-megabyte files, expect smooth validation but slow textarea editing. For gigabyte-scale data, validate in Node with the ajv CLI instead.

Free Tool

JSON Schema Validator (2026)

Validate JSON data against a JSON Schema. Powered by Ajv — the most-installed schema validator on npm. Supports drafts 04 through 2020-12. Pure browser.

Paste schema and data to validate

JSON Schema

Data to validate

When to validate against a schema

Before sending a request body to an API — catch issues client-side instead of getting a 400.
After receiving a response from an untrusted upstream — guarantee the shape your code expects.
In CI against test fixtures — make sure your test data still matches the schema as you evolve it.
In docs — Specway validates every example payload in your OpenAPI spec at build time. If an example doesn't match its declared schema, the build fails.

JSON Schema vs OpenAPI schema

The schemas in your openapi.yaml's components/schemas section are JSON Schema — with some constraints depending on OpenAPI version. OpenAPI 3.0 uses a draft-04-ish dialect; OpenAPI 3.1 fully aligns with JSON Schema 2020-12. Either way, you can paste a schema from your spec and validate request/response bodies against it with this tool.

What the validator catches

Type errors — string where number expected, object where array expected.
Missing required fields.
Out-of-range values — minimum, maximum, minLength, maxLength.
Pattern violations — regex on strings.
Format violations — email, uri, date-time, uuid (with ajv-formats).
Enum violations — values outside the allowed set.
Additional properties when additionalProperties: false.

Ship API docs that stay this clean

Specway turns your OpenAPI spec into a branded developer portal — auto-synced, searchable, with built-in playground and code samples in every language. Free tier available.

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Frequently asked questions

When to validate against a schema

Before sending a request body to an API — catch issues client-side instead of getting a 400.
After receiving a response from an untrusted upstream — guarantee the shape your code expects.
In CI against test fixtures — make sure your test data still matches the schema as you evolve it.
In docs — Specway validates every example payload in your OpenAPI spec at build time. If an example doesn't match its declared schema, the build fails.

JSON Schema vs OpenAPI schema

What the validator catches

Type errors — string where number expected, object where array expected.
Missing required fields.
Out-of-range values — minimum, maximum, minLength, maxLength.
Pattern violations — regex on strings.
Format violations — email, uri, date-time, uuid (with ajv-formats).
Enum violations — values outside the allowed set.
Additional properties when additionalProperties: false.

When to validate against a schema

Before sending a request body to an API — catch issues client-side instead of getting a 400.
After receiving a response from an untrusted upstream — guarantee the shape your code expects.
In CI against test fixtures — make sure your test data still matches the schema as you evolve it.
In docs — Specway validates every example payload in your OpenAPI spec at build time. If an example doesn't match its declared schema, the build fails.

JSON Schema vs OpenAPI schema

What the validator catches

Type errors — string where number expected, object where array expected.
Missing required fields.
Out-of-range values — minimum, maximum, minLength, maxLength.
Pattern violations — regex on strings.
Format violations — email, uri, date-time, uuid (with ajv-formats).
Enum violations — values outside the allowed set.
Additional properties when additionalProperties: false.

When to validate against a schema

Before sending a request body to an API — catch issues client-side instead of getting a 400.
After receiving a response from an untrusted upstream — guarantee the shape your code expects.
In CI against test fixtures — make sure your test data still matches the schema as you evolve it.
In docs — Specway validates every example payload in your OpenAPI spec at build time. If an example doesn't match its declared schema, the build fails.

JSON Schema vs OpenAPI schema

What the validator catches

Type errors — string where number expected, object where array expected.
Missing required fields.
Out-of-range values — minimum, maximum, minLength, maxLength.
Pattern violations — regex on strings.
Format violations — email, uri, date-time, uuid (with ajv-formats).
Enum violations — values outside the allowed set.
Additional properties when additionalProperties: false.