Validate JSON syntax instantly and get clear, actionable error messages when something is wrong. JSON is the backbone of modern web APIs, configuration files, and data interchange, but even a single misplaced comma, missing quote, or unescaped character can cause parsing failures that are difficult to debug from generic error messages. This tool uses the browser's native JSON parser to check your input and pinpoints exactly where syntax errors occur. When valid, it displays a formatted, pretty-printed version ready to copy. All validation runs entirely client-side in your browser — your data never leaves your device, making it safe for sensitive configurations and API payloads.
Valid JSON
About JSON Validator
The JSON Validator checks whether your text is syntactically valid JSON according to the official specification (RFC 8259). It catches common errors including: missing or mismatched brackets and braces, trailing commas (not allowed in strict JSON), unquoted keys (JSON requires double-quoted strings), single quotes instead of double quotes, invalid escape sequences, and unexpected characters. When an error is found, the tool displays the native parser error message with the approximate position, helping you locate and fix the problem quickly. When the JSON is valid, it's automatically formatted with clean indentation so you can copy a readable version. All processing runs in your browser. For comprehensive JSON formatting, see our JSON Formatter, and for comparing JSON documents, try our JSON Diff.
How to Use JSON Validator
- Paste or type your JSON into the JSON input area.
- Click Validate JSON to check the syntax.
- If the JSON is invalid, read the error message and position indicator to locate and fix the problem.
- If valid, the formatted JSON is displayed — click Copy formatted to copy the clean, indented version.
Key Features
- Strict syntax validation — Checks JSON against the official RFC 8259 specification using the browser's native parser.
- Detailed error messages — Displays the exact error and approximate position to help you fix problems quickly.
- Auto-formatting — Valid JSON is automatically pretty-printed with indentation for easy reading.
- Common error detection — Catches trailing commas, unquoted keys, single quotes, missing brackets, and invalid escapes.
- One-click copy — Copy the validated, formatted JSON to your clipboard instantly.
- Browser-based privacy — All validation runs locally with no server upload or data collection.
When to Use This Tool
- Checking API request or response payloads before sending or processing them.
- Validating configuration files (e.g., package.json, tsconfig.json) after manual editing.
- Debugging "unexpected token" errors by finding the exact location of the syntax problem.
- Verifying JSON data exports before importing them into databases or other systems.
- Quick-checking JSON snippets from documentation, tutorials, or code examples.
Technical Details
The validator uses JavaScript's built-in JSON.parse() function, which implements strict JSON parsing according to the ECMA-404 / RFC 8259 standard. This means: all strings must be double-quoted, no trailing commas are allowed, no comments are permitted, and all escape sequences must be valid. The native parser provides error messages that include the character position where parsing failed, which helps pinpoint the issue. When validation succeeds, the parsed object is re-serialized with JSON.stringify(null, 2) for clean 2-space indentation. Note that this validates syntax only — it does not validate against a JSON Schema. For schema validation, dedicated tools or libraries are needed.
Conclusion
The JSON Validator is a fast, reliable way to catch syntax errors in your JSON before they cause problems in your applications. With detailed error messages, auto-formatting of valid JSON, and complete browser-based privacy, it's an essential tool in every developer's workflow.