About JSON Validator

Validate JSON syntax and structure. Part of the DevTools Surf developer suite. Browse more tools in the JSON collection.

Use Cases

• Confirm an API response is valid JSON before parsing
• Find the exact line/position of a parse error in a large payload
• Verify config files (package.json, tsconfig) before committing
• Catch malformed JSON from user uploads before downstream processing

Tips

• It detects and auto-corrects common issues: comments, unquoted keys, trailing commas
• Validation errors show the exact position of the problem
• Pair with JSON Schema to validate structure, not just syntax

Fun Facts

• The JSON specification is only 10 pages long — one of the shortest data format specs ever written.
• JSON technically allows duplicate keys in objects, but the behavior is undefined — different parsers handle them differently.
• ECMA-404, the JSON standard, was approved in just 3 months — the fastest ECMA standard ever ratified.

FAQ

What counts as invalid JSON?

Anything that deviates from RFC-8259: comments, single quotes, trailing commas, unquoted keys, duplicate keys in strict mode, NaN/Infinity, or unescaped control characters. The validator points to the exact line and column.

Does this auto-fix errors or just report them?

It does both. Common issues (comments, trailing commas, unquoted keys, single quotes) are auto-corrected and you can copy the fixed output; the error list shows what was repaired.

Can I validate against a JSON Schema?

This tool only validates syntax. For structural validation use the dedicated JSON Schema validator — or wire both into your build pipeline in sequence.

Why does my JSON validate here but fail in another parser?

Strict parsers reject duplicate keys, BOM bytes, and certain Unicode sequences. Run through this validator first to normalize, then test in the target environment.