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Validation

JSON Validator

Check whether JSON is valid before it breaks a deployment, import, or API request.

Open JSON ValidatorAll tools
  • Fast syntax feedback
  • Works directly in the editor
  • Pairs naturally with debugger tools

Practical guide

Build, validate, and reuse JSON with less friction.

A focused walkthrough for deciding when the tool fits your workflow.

The JSON Validator checks your JSON syntax and reports exactly where it breaks — giving you line numbers, error descriptions, and context so you can fix problems before they reach production. It runs entirely in the browser, which means sensitive payloads never leave your machine. Whether you're checking an API request body, a config file, or a third-party data import, validation is the fastest way to rule out syntax as the source of a bug.

How to use the JSON Validator

  1. Paste or type your JSON into the editor.
  2. The validator parses the input continuously and highlights the first syntax error it finds.
  3. Read the error message — it tells you the line number and what the parser expected versus what it found.
  4. Fix the issue directly in the editor. The error clears as soon as the syntax is corrected.
  5. Once validation passes, use the JSON Formatter to clean up indentation, or the JSON Debugger to explore the structure.

What it fixes

  • Missing or trailing commas between key-value pairs or array items
  • Unmatched brackets — a { that has no closing }
  • Single-quoted strings instead of double-quoted (a very common mistake)
  • Unescaped special characters inside string values
  • undefined, NaN, or Infinity values that are valid in JavaScript but not in JSON
  • Bare keys that aren't wrapped in quotes (also valid in JS, not in JSON)

Before and after

Before — invalid JSON with two common mistakes:

JSON
{
  "status": "active",
  "count": 42,
  "tags": ["billing", "premium",],
  "owner": 'Dana'
}

After — corrected, valid JSON:

JSON
{
  "status": "active",
  "count": 42,
  "tags": ["billing", "premium"],
  "owner": "Dana"
}

The trailing comma after "premium" and the single-quoted string around Dana are both hard to spot by eye and will both silently break most JSON parsers. The validator catches them immediately.

When to use it

Before sending an API request — a malformed request body returns a 400 error that tells you nothing useful. Validate first so you know the body itself isn't the problem.

During config file changes — environment configs, feature flag files, and schema files are often hand-edited. A single misplaced comma breaks everything. Validate before committing.

At QA handoff — if a developer hands a test payload to a QA engineer, validate it first. Broken payloads waste testing cycles on a problem that isn't a product bug.

When ingesting third-party data — external JSON feeds and export files are often malformed. Validating before importing saves debugging time downstream.

For a deeper explanation of what separates valid from invalid JSON, see Valid vs Invalid JSON. For a list of the most frequent errors developers encounter, see Common JSON Mistakes.

FAQ

Questions about JSON Validator

Everything you need to know before you start.

The most common causes are: a trailing comma after the last item in an object or array, single quotes instead of double quotes, an unquoted key, a comment (JSON has no comment syntax), or a JavaScript-only value like undefined or NaN. The validator will point to the exact line and character where the error occurs.

Not necessarily. JSON can be syntactically valid — it parses without error — but still contain wrong data for your use case, like a negative age or an invalid email address. Syntax validation confirms the format is correct. Data validation (using JSON Schema) confirms the values are correct.

No. JSON Prism's validator runs entirely in your browser using the native JSON.parse() function. Your JSON is never sent to a server. This makes it safe to validate sensitive data like API keys, credentials, or personal information.

JSONC is JSON with comments — it allows // and /* */ comment syntax. It is used by VS Code for settings.json and tsconfig.json. Standard JSON validators will reject JSONC because the JSON specification does not permit comments. Strip comments before validating, or use a JSONC-aware tool.

Ready to use it?

JSON Validator, free & private.

No account needed. Your JSON never leaves your browser.

Launch JSON Validator