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JSON Validator

Check whether text is valid JSON — get a clear pass, or the parser's error if it is not.

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Quick Answer

JSON Validator checks whether your text is well-formed JSON, in your browser. Paste it and you either get a clear Valid JSON confirmation — with a tidy, formatted copy — or the parser's error message pointing to what went wrong. It enforces the strict JSON standard, so comments, trailing commas, single quotes, and unquoted keys all count as invalid. Nothing is uploaded.

What the JSON Validator Does

Before you ship a config, send a payload, or trust a file, it helps to know it is actually valid JSON. This tool gives you a straight answer: paste the text and it tells you pass or fail, and if it fails, it shows the error so you can find the problem.

It validates by parsing — the same way your code will — so a pass here means a real JSON parser accepts it. As a bonus, valid input is returned neatly formatted, so you can eyeball the structure at the same time.

How It Works

The tool runs your text through the browser's built-in JSON parser. If the parser accepts it, the JSON is valid and you see the confirmation; if the parser throws, the JSON is invalid and you see its error message instead.

Validity is judged against the strict JSON standard. That means double-quoted keys and strings, no comments, no trailing commas, and no single quotes — exactly the rules a conforming parser enforces.

What it checks & how

  1. Step 1. Paste the text you want to check — it stays in your browser, never uploaded.
  2. Step 2. The browser's JSON parser attempts to read it.
  3. Step 3. If it parses, you get a Valid JSON confirmation and a formatted copy.
  4. Step 4. If it fails, the parser's error message shows what broke and roughly where.
  5. Step 5. Fix the flagged spot and validate again.

Privacy

Validation runs entirely on your device — your text is never uploaded. That is important when you are checking a real request body, a config, or anything with secrets or personal data in it.

Nothing is stored and there is no account. Clear the box or close the tab and your input and any output leave memory.

Technical Details

EngineBrowser JSON parser (strict)
VerdictValid JSON, or the parser's error
On validAlso returns a formatted copy
ChecksSyntax (well-formedness), not schema
AcceptsStandard JSON only
UploadNever — runs in your browser

Standards & references

  • ECMA-404 / RFC 8259 (JSON) — the standards that define valid JSON; this tool accepts exactly what a conforming parser accepts.
  • Strict JSON rules — double-quoted keys and strings, no comments, no trailing commas, no single quotes — anything else is reported invalid.

Accuracy & Limitations

A pass means your text parses as standard JSON — the same check your application's parser performs. It is a reliable yes/no for well-formedness.

It validates syntax, not meaning. It cannot know whether your JSON has the right keys, types, or values for your use — that is schema validation, a separate job. Valid JSON can still be wrong data.

The error message comes from the browser's JSON parser, so its wording and the position it cites depend on your browser. It reliably flags that something is invalid and points you near it, but it will not always explain the cause in plain English.

It is strict by standard. Comments, trailing commas, single quotes, and unquoted keys are all reported as invalid even though some tools tolerate them — if you need those, you are working with JSON5 or JS objects, not standard JSON.

Real-World Use Cases

Catch a syntax error

Find the stray comma or bracket that is breaking a config or payload.

Verify before sending

Confirm a request body is valid JSON before an API rejects it.

Check pasted data

Make sure JSON copied from a log or chat was not truncated or mangled.

Teach JSON syntax

See immediately why an example is or is not valid.

When to use it — and when not to

Good for

  • A clear valid/invalid answer
  • Finding a syntax error's rough location
  • Confirming standard (strict) JSON
  • A formatted copy when it passes

Not the best choice for

  • Checking JSON against a schema (keys/types)
  • Validating JSON5 or relaxed syntax
  • Explaining every error in plain English
  • Linting style or formatting rules

To enforce required keys and types, use a JSON Schema validator; to just tidy valid JSON, the JSON formatter does that (and also flags invalid input).

Frequently Asked Questions

How does it check validity?
It runs your text through the browser's JSON parser. If the parser accepts it, it is valid JSON; if the parser throws an error, it is not — and you see that error.
What counts as invalid?
Anything outside strict JSON: comments, trailing commas, single-quoted strings, unquoted keys, or a stray or missing bracket, brace, or comma. All of those make standard JSON parsing fail.
Does it check my data against a schema?
No. It checks syntax — whether the text is well-formed JSON — not whether it has the right keys, types, or values. That is schema validation, a separate tool.
Why does it also show formatted JSON?
When your input is valid, the tool returns a pretty-printed copy so you can read the structure while you confirm it is valid. Invalid input shows the error instead.
The error is hard to understand — why?
It is the browser's own parser error, so the exact wording varies by browser. It tells you parsing failed and roughly where; check near that position for a missing comma, quote, or bracket.
Will it accept JSON with comments?
No. Comments are not part of standard JSON, so they are reported invalid. The same goes for trailing commas and single quotes — those belong to JSON5 or JavaScript, not JSON.
Can valid JSON still be wrong?
Yes. Valid means well-formed syntax. The data can still have the wrong fields or values for your application — that is correctness, which a validator cannot judge.
Is my JSON uploaded?
No. It is validated entirely in your browser. Nothing is sent to a server, and clearing the box removes it.
Is there a size limit?
No fixed limit. Validation runs in your browser, so very large inputs depend on your device, but typical files check instantly.
What is the difference from the JSON formatter?
They overlap: both parse your JSON. The validator leads with a clear valid/invalid verdict and the error; the formatter leads with the pretty-printed output. Either one rejects invalid JSON.

References

Reflects what the tool really does — parse-based validation against strict JSON — including that it checks syntax, not your data's schema.

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