JSON Schema Validator

About the JSON Schema Validator playground

The JSON Schema Validator checks whether a JSON document conforms to a JSON Schema you provide. Paste your schema and your data side by side and the tool validates the instance entirely in your browser, reporting every constraint that fails: wrong types, missing required properties, values outside allowed ranges, pattern mismatches, and more. This is invaluable for verifying API payloads, configuration files, and data contracts so you can catch malformed data before it flows through your application.

JSON Schema is a declarative vocabulary, defined by the json-schema.org specifications, for describing the structure of JSON data. A schema specifies expected types, required fields, value constraints (minimum, maximum, pattern, enum), and nested object and array shapes. Validation compares a concrete JSON instance against that schema and produces a pass or a list of violations. Using schemas turns informal assumptions about your data into machine-checkable rules, improving reliability and making it easy to document and enforce the shape of the data your systems exchange.

HostedJSON Schema Validator runtime

mainentry file

single fileworkspace

stdinprogram input

How it works

Write

The main file is the entry point for each run.

Give it input

Use the Input panel to pipe standard input to your program when it needs data.

Run

Run sends your code to a fresh hosted runtime and streams the result into the output panel.

Keep or share

Your draft stays in this browser, and Share creates a separate snapshot link.

External resources

json-schema.org— Official website
GitHub— Official spec repository

Schema with required fields

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

Valid instance

Data:
{ "name": "Ada", "age": 36 }

Result: Valid — all required fields present and types match.

Invalid: missing required field

Data:
{ "name": "Ada" }

Result: Invalid — missing required property "age".

Invalid: type and constraint errors

Data:
{ "name": "Ada", "age": -5 }

Result: Invalid — "age" violates "minimum": 0 (and must be an integer).

Enum and pattern schema

Schema:
{
  "type": "object",
  "properties": {
    "role": { "enum": ["admin", "user"] },
    "code": { "type": "string", "pattern": "^[A-Z]{3}$" }
  }
}

Valid: { "role": "admin", "code": "ABC" }
Invalid: { "role": "guest", "code": "ab" } — role not in enum; code fails the pattern.

Array constraints

Schema:
{
  "type": "array",
  "items": { "type": "number" },
  "minItems": 1,
  "uniqueItems": true
}

Valid: [1, 2, 3]
Invalid: [1, 1] — fails "uniqueItems"; [] — fails "minItems": 1.

Nested object schema

Schema:
{
  "type": "object",
  "properties": {
    "user": {
      "type": "object",
      "required": ["id"],
      "properties": { "id": { "type": "integer" } }
    }
  }
}

Valid: { "user": { "id": 7 } }
Invalid: { "user": { "id": "7" } } — nested "id" must be an integer, not a string.

additionalProperties: false

Schema:
{
  "type": "object",
  "properties": { "name": { "type": "string" } },
  "additionalProperties": false
}

Valid: { "name": "Ada" }
Invalid: { "name": "Ada", "extra": 1 } — "extra" is not a defined property.

Format and string length

Schema:
{
  "type": "object",
  "properties": {
    "email": { "type": "string", "format": "email" },
    "pin": { "type": "string", "minLength": 4, "maxLength": 4 }
  }
}

Valid: { "email": "[email protected]", "pin": "1234" }
Invalid: { "email": "a@b", "pin": "12" } — bad email format; pin too short.

JSON Schema

JSON Data

Write

Give it input

Run

Keep or share

Editing

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