JSON Schema Validator

How to use JSON Schema Validator

1. Paste a schema into JSON Schema and the data to check into JSON document, or load files with Open schema and Open JSON. Try an example loads a schema with a document that breaks several rules.
2. Pick the Draft: Auto ($schema) reads the schema’s $schema, or force 2020-12 or Draft-07. Untick Check formats (date-time, email, ipv4, uuid, uri…) to treat format as a hint only.
3. Read the result: the status line says whether the document is valid, and each error lists the failing location in the document, a message and the schema path. Copy errors copies the list.
4. No schema yet? Paste a sample document and press Generate schema from JSON, then edit the generated schema and use Copy schema.

How it works

Validation is done by a validator built into the tool, running in a background worker. It supports draft 2020-12 and draft-07 (draft-04 and draft-06 schemas are checked with draft-07 rules, and 2019-09 with 2020-12). Supported keywords include type, enum, const, number and string limits, pattern, items/prefixItems/additionalItems, contains with minContains/maxContains, uniqueItems, properties, patternProperties, additionalProperties, propertyNames, required, dependentRequired, dependentSchemas and dependencies, allOf, anyOf, oneOf, not and if/then/else. Every error is reported, not just the first.

$ref resolves inside the same schema: JSON Pointers such as #/$defs/address, $defs and definitions, $anchor, and $id-based references. In draft-07, keywords next to a $ref are ignored, as the spec says. String lengths count Unicode characters, so an emoji counts as one, and pattern uses JavaScript regular expressions with Unicode support and is not anchored. With format checking on, date-time, date, time, email, ipv4, ipv6, uuid and uri are checked; other formats are ignored.

Generate schema from JSON infers a schema that your sample passes. It records the types it finds, nested object properties, and array items merged across all elements. Keys present in every object are marked required, and string formats such as date-time, email or uuid are added when every value matches. Mixed types become a type list, or anyOf when objects or arrays are involved.

Limits

• Remote schemas are never fetched. A $ref to another URL or file is reported as unresolvable.
• unevaluatedProperties and unevaluatedItems aren’t supported and are ignored with a notice. $dynamicRef is resolved like a plain $ref.
• Validation is stopped after 3 seconds, for example when a pattern backtracks catastrophically.
• At most 500 errors are listed. Schemas that recurse more than 300 levels, such as a $ref loop, report an error instead of hanging.
• Both inputs are read with the browser’s standard JSON parser for validation, so integers beyond 2^53 are compared after rounding. Opened or dropped files are limited to 10 MB.
• The generated schema only reflects your sample. It never adds additionalProperties: false, enum, number ranges or string lengths.

Privacy

Validation and schema generation run entirely in your browser, in a background worker; nothing is uploaded or stored, and remote $refs are never fetched. Share copies a link with both inputs and the options in the URL’s # fragment, which browsers don’t send to servers, though anyone with the link can read it. JSON sent here from another tool with Send to… goes into the document box through this tab’s session storage and is removed as soon as it is read.

Frequently asked questions

Which JSON Schema drafts are supported?

Draft 2020-12 and draft-07. With Auto ($schema), the draft is read from the schema’s $schema and defaults to 2020-12. Draft-04 and draft-06 schemas are checked with draft-07 rules and 2019-09 with 2020-12 rules, with a notice.

Why does an invalid email pass validation?

Only when Check formats is off. The JSON Schema spec treats format as an annotation by default, so many validators skip it. With the option on, the tool checks email, date-time, date, time, ipv4, ipv6, uuid and uri.

Can my schema reference another schema file?

Not yet. $ref resolves within the pasted schema only, using $defs, definitions, JSON Pointers, $anchor or $id. References to other URLs are reported as unresolvable and are never downloaded. Copy the referenced definitions into $defs instead.

Why did validation stop after a few seconds?

A pattern like ^(a+)+$ can take exponential time on some strings. The validator runs in a worker and is stopped after 3 seconds so the page stays responsive. Simplify the pattern and validation resumes as you type.

How do I read the error paths?

The first path is a JSON Pointer into your document, such as /address/zip, or (root) for the whole document. The second is the schema keyword that failed, such as #/$defs/address/properties/zip/pattern. With $ref, it points at the referenced definition.