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Validate any schema. Any format. Instantly.

JSON Schema · OpenAPI · GraphQL · Avro · Protobuf · YAML · XML · XSD · JSON-LD · TOML

Runs 100% in your browser — your schema never leaves your device

A free online schema validator for every format

schemavalidator.dev is a free, browser-based schema validator that checks whether your schema is well-formed and conforms to its specification — and tells you exactly where it isn't. Paste or open a schema, pick the format, and get line-precise errors in an instant, with no sign-up and nothing to install. It is built for the developers, API designers and data engineers who write and review schemas every day and just want fast, trustworthy feedback.

Most validation tools cover a single format, so you end up bouncing between a different site for JSON Schema, OpenAPI, GraphQL, YAML and the rest — each with its own layout, quirks and unknown privacy posture. This tool brings them together: JSON Schema, OpenAPI/Swagger, GraphQL SDL, YAML, Avro, Protobuf, XML, XSD, JSON-LD and TOML, all behind one consistent editor and error display.

Crucially, every check runs entirely in your browser. Your schema is never uploaded to a server, so you can validate proprietary API contracts and internal data models with zero exposure — the privacy guarantee is built into how the tool works, not a policy you have to trust. The about page sets out what runs locally and what is measured.

Frequently asked questions

What is a schema validator?

A schema validator checks whether a document conforms to a predefined schema — a set of rules describing the structure, data types and constraints the document is expected to follow. It catches problems early: structural errors, missing required fields, wrong types, malformed values and references to things that were never defined, all before that schema reaches your build, API or data pipeline. There are two related jobs people call validation. The first is checking that the schema document itself is well-formed and conforms to its specification — for example, that a JSON Schema is valid against the chosen draft, or that an OpenAPI description matches the OpenAPI meta-schema. The second is checking a separate data instance against that schema. This tool does both, with the balance depending on the format: for every format it tells you whether the schema you wrote is itself correct, with clear, line-aware error messages, and for XML it also checks a document against an XSD 1.0 schema.

What formats are supported?

JSON Schema, OpenAPI/Swagger, GraphQL SDL, YAML, Avro, Protobuf, XML, XSD, JSON-LD, and TOML — each with a dedicated validator page. See the JSON Schema, OpenAPI, GraphQL, YAML, Avro, Protobuf, XML, XSD, JSON-LD, and TOML validators.

Is my schema sent to a server?

No. Every validator on this site runs entirely in your browser, in client-side JavaScript, so your schema content never leaves your device — there is no upload step and no server that receives it. The validation libraries are loaded into the page and execute locally on the text you paste or open; your schema is never transmitted, logged or stored on our end. That makes the tool safe for internal API specifications, proprietary data models and other schemas you cannot post to a public service. It also keeps things fast, since there is no network round trip between typing and seeing results. The only time data leaves your browser is if you choose to create a share link, which encodes the schema into the URL itself — so treat a share link exactly as sensitively as the schema it contains.

Why one tool for many formats?

Every format normally has its own validator with its own UX and error style. schemavalidator.dev gives one consistent interface across all of them.

Can I validate data against a schema?

For XML, yes: an XML document can be validated against an XSD 1.0 schema at /validate/xsd/. For the other formats the current version validates that the schema itself is well-formed; instance-against-schema validation for those is on the roadmap.