JSON Validator

What is the JSON Validator?

The JSON Validator checks whether a document is well-formed JSON and, when you supply a JSON Schema, whether it also conforms to that schema. The first check catches syntax mistakes; the second catches structural ones, such as a missing required field or a value of the wrong type.

There are two distinct questions you can ask about a JSON document. The first is whether it parses at all: whether the brackets balance, the strings are quoted correctly, and there are no stray commas. The second is whether the parsed data has the shape your application expects.

A document can pass the first check and fail the second. {"port": "5432"} is perfectly valid JSON, but if your schema says port must be an integer, it is still wrong for your purposes. This tool reports both classes of problem.

How to use the JSON Validator

1. Paste the document to validate. Put your JSON into the input editor. Syntax validation runs against it immediately.
2. Optionally supply a JSON Schema. If you want structural validation as well, paste a schema into the schema editor. Draft 7 and the 2019-09 and 2020-12 drafts are supported.
3. Read the results. Syntax errors are reported with a line and column. Schema violations are reported per offending property, with the path to the value that failed and the constraint it broke.
4. Fix and revalidate. Edit the input and the checks re-run, so you can work through a list of violations one at a time.

Worked examples

// Schema
{
  "type": "object",
  "required": ["name", "age"],
  "properties": {
    "name": { "type": "string" },
    "age": { "type": "integer", "minimum": 0 }
  }
}

// Document
{ "name": "Grace Hopper", "age": "45" }

Valid JSON syntax.
Schema validation failed:
  /age: must be integer (got string)

{ "name": "Katherine Johnson" }

Valid JSON syntax.
Schema validation failed:
  /: must have required property 'age'

Common use cases

• Verifying API contracts. Paste a real response and the schema it is supposed to satisfy to confirm the server is honouring the contract before you write client code against it.
• Checking configuration before deployment. Many tools ship a JSON Schema for their config format. Validating locally catches a typo that would otherwise fail at service start.
• Developing a schema. When writing a schema, testing it against known-good and known-bad documents is the quickest way to confirm the constraints do what you intended.
• Reviewing third-party data. Before importing a data dump, validating it against an expected shape tells you whether the import will succeed without running it.

Features and limitations

• Reports syntax errors with line and column positions.
• Supports JSON Schema draft 7, 2019-09, and 2020-12.
• Lists every schema violation rather than stopping at the first one, so you can see the full extent of a problem.
• Identifies failures by JSON Pointer path, which makes nested violations unambiguous.
• Schema $ref resolution is limited to references within the supplied schema document. Remote references over HTTP are not fetched, since the tool makes no network requests.
• Custom format validators beyond the standard set are not supported.

Frequently asked questions