Does valid JSON mean my API call will work?

No, and the distinction matters. Validity is purely about syntax — a parser will accept it. Whether the fields are the ones the API needs, in the types it expects, is schema validation, which is a different question and needs a JSON Schema or the API's own documentation to answer.

Is a top-level array or a bare string valid JSON?

Yes to both, under RFC 8259. Older parsers written against the original spec insisted on an object or array at the root, so `"hello"` or `42` alone will be rejected by some very old libraries — but by the current standard they are perfectly valid JSON documents.

Is my JSON uploaded to be validated?

No. The parsing happens in this page using the browser's own JSON parser, so nothing is transmitted. That matters more here than on most tools, because the JSON people need to validate is usually a real API response with real customer data in it.

JSON Validator

Paste JSON and find out immediately whether a parser will accept it — and if not, exactly where it breaks. Rather than repeating the engine's message, this points at the failing line with a caret and names the usual culprits: a trailing comma, single quotes, a stray comment, or a JavaScript value like NaN that JSON has no concept of. When the document is valid it describes what's actually in it, so you can see whether it's the payload you expected.

Your text

Describe the structure when it's valid

Lists the top-level keys and their types, so you can see at a glance whether it's the document you expected.

Result

Nothing is uploaded — this tool runs inside your browser, so your files never leave your device.

Help us improve

Why use this tool

Marks the failing line and column with a caret
Names the likely cause — trailing comma, single quotes, comments, NaN
Summarises the top-level keys and their types when the JSON is valid
Runs in your browser, so API responses with real data stay on your machine

How it works

1Paste the JSON you want checked.
2If it's invalid, read the marked line and the suggested cause underneath.
3Fix it and paste again — a parser stops at the first error, so there may be more.

JSON Validator — frequently asked questions

Four causes account for nearly all of it. A trailing comma before a closing bracket, which JavaScript allows and JSON does not. Single-quoted strings — JSON requires double quotes, on keys as well as values. Comments, which JSON has none of. And JavaScript values like NaN, Infinity or undefined, which have no JSON representation. This tool checks for all four and says which it found.

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