JSON Validator

About the JSON Validator playground

The JSON Validator checks whether a document is valid JSON and reports any syntax errors with line and position information so you can fix them quickly. It parses the input against the JSON grammar and flags the exact problem, such as a missing comma, an unterminated string, a trailing comma, or an unquoted key. JSON (JavaScript Object Notation) is a strict, lightweight data format built from objects, arrays, strings, numbers, booleans, and null, and it powers most web APIs and config files.

Validation runs entirely in your browser, so your data is never uploaded or stored on a server, making it safe for payloads that contain sensitive values. Paste a document and instantly learn whether it is well-formed, with a clear error message pointing at where parsing failed. This is ideal for catching malformed API responses, debugging hand-edited config, or confirming a generated file is correct before it is consumed downstream.

HostedJSON 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.org— Format reference

Valid JSON

{
  "name": "Ada",
  "tags": ["a", "b"],
  "active": true
}

Invalid: trailing comma

{
  "name": "Ada",
  "active": true,
}
// Error: unexpected '}' after trailing comma

Invalid: unquoted key

{
  name: "Ada"
}
// Error: property keys must be double-quoted strings

Invalid: single quotes

{ 'name': 'Ada' }
// Error: strings must use double quotes, not single

Valid: nested structure

{
  "user": {
    "id": 1,
    "roles": ["admin", "editor"],
    "meta": null
  }
}
// Valid: objects and arrays may be nested; null is a permitted value

Invalid: missing comma

{
  "a": 1
  "b": 2
}
// Error: expected ',' or '}' after value; members must be comma-separated

Invalid: leading zero / NaN

{ "qty": 007, "price": NaN }
// Error: numbers may not have leading zeros and NaN is not valid JSON

Valid: array of objects

[
  { "id": 1, "ok": true },
  { "id": 2, "ok": false }
]
// Valid: a top-level array is legal JSON; each element is a complete object

Invalid: comment present

{
  "a": 1 // a count
}
// Error: comments are not part of JSON; remove the // ... text

Input

Issues

No input to validate

Write

Give it input

Run

Keep or share

Editing

Navigation

Selection