JSON Validate — Free Online Tool

A JSON validator checks whether a JSON document is syntactically valid (parsable) so your payloads don’t fail at runtime. It catches missing quotes, trailing commas, invalid escapes, and mismatched brackets—common issues when copying request bodies, building fixtures, or editing config. SWEDevTools: Prism validates locally in your browser, so you can test sensitive API payloads without uploading them anywhere.

Features

• Strict JSON parsing: Rejects comments and trailing commas so output matches standard JSON parsers.
• Great for API debugging: Validate request/response bodies when working with SDKs, tests, and incident logs.
• Local-first privacy: Useful when payloads include tokens, IDs, or PII you shouldn’t paste into online tools.
• Fast feedback loop: Quickly confirm whether a “JSON parse error” is caused by formatting or corruption.

Frequently Asked Questions

Why does my object fail JSON validation?

Some formats allow non-JSON features (single quotes, comments, trailing commas). Strict JSON requires double quotes and no comments/trailing commas.

Does this validate JSON Schema?

No. This validates JSON syntax only. Schema validation enforces types and required fields.

Are trailing commas allowed in JSON?

No. Trailing commas are invalid in strict JSON.

Can JSON contain NaN or Infinity?

No. JSON numbers must be finite. Use null or strings if you need sentinel values.

How do I represent a newline in a JSON string?

Use \n. Literal newlines inside a JSON string are invalid.

Why do I get “unexpected token” errors?

Usually it’s a missing comma, missing quote, or an extra character after the document ends.

Is JSON always UTF-8?

Most tooling assumes UTF-8. Ensure file encoding is correct to avoid hidden character issues.

How do I debug huge JSON?

Use binary search: remove half the payload, validate, and repeat. Or isolate sections around the failure.

What happened to smalldev.tools?

smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.

Is Prism a good alternative to jsonformatter.org?

Yes. Prism offers the same JSON formatting and validation capabilities with full offline support, pipeline chaining, and zero ads. Your data never leaves your browser, unlike most online JSON tools.

How does Prism compare to jsonlint.com?

Prism provides all the JSON linting features of jsonlint.com plus offline processing, tool chaining, and complete data privacy. No data is ever uploaded to a server.