EasyDeveloper

JSON Validator

Validate JSON and pinpoint the first error with a line, column and plain-English explanation.

Local ProcessingYour data stays in your browser. Nothing is uploaded.

An API response arrives, a config file gets edited by hand, a colleague pastes JSON into a ticket - and something does not parse. The JSON Validator runs your document through the same parser your browser uses and tells you, in plain language, where the first problem is and what most likely caused it.

Paste JSON and press Validate. A valid document gets a clean confirmation with its byte size. An invalid one gets the line and column of the first error, a short snippet of the surrounding text, and a best-effort explanation - a trailing comma, a single-quoted string, a leftover comment or a non-finite number are the usual suspects, and each is described with how to fix it.

Validation happens entirely in your browser. The document never leaves your device, so you can check a payload that contains tokens or internal config without a second thought about where the text is going.

The validator also catches a classic copy-paste trap: a document that looks fine in an editor but fails the instant a real parser touches it. Some tools quietly tolerate invalid input or auto-correct it, which hides problems until they surface in production. Here you get the strict verdict of the same engine your own code will run, so what you see is what your application will experience.

Features

  • Validate JSON instantly and get a clear pass or fail result.
  • Pinpoint the first error with an exact line and column, not a vague message.
  • Get a plain-English explanation of the most likely cause - trailing commas, single quotes, comments and more.
  • See a trimmed snippet of the document around the error so you know exactly where to look.
  • Works with large documents: validation is a single native parse pass.
  • Confirms valid documents with their byte size, so you know the payload you are about to ship is sound.
  • No signup and no install - open the page, paste and validate.
  • Everything runs locally - nothing is uploaded, stored or tracked.

How to Use

  1. 1

    Paste your JSON

    Copy the document into the input area. It can come from an API response, a config file or a log line - the validator does not care where it came from.

  2. 2

    Press Validate

    Hit Validate (or press Ctrl+Enter). The result appears immediately: a green confirmation for valid documents, or a red error block that locates the first problem.

  3. 3

    Read the error

    For invalid input, the report shows the line and column, a short context snippet and a plain-English explanation of the likely cause. Use the context snippet to jump straight to the offending text.

  4. 4

    Fix and re-check

    Edit the input and validate again. The parser re-runs in a single pass, so iterating is fast even on long documents.

Example

Valid JSON

{"name":"Alice","age":30,"items":[1,2,3]}

↓

✓ Valid JSON
Size: 42 bytes

Invalid - trailing comma

{"name":"Alice","age":30,}

↓

✗ Invalid JSON
Line 1, Column 25
Explanation: A trailing comma. JSON does not allow a comma after the last item in an object or array.

Invalid - single quotes

{'name':'Alice'}

↓

✗ Invalid JSON
Line 1, Column 2
Explanation: Single quotes around a string. JSON strings must use double quotes.

Common Problems

Trailing commas

A comma after the last property or array element is invalid in JSON even though it is legal in JavaScript. The validator flags it at the exact position of the closing bracket.

Single-quoted strings

JSON strings must use double quotes. 'name' is valid JavaScript but not valid JSON - replace the single quotes with double quotes and escape any inner quotes.

Comments left in the document

JSON has no comment syntax. If you converted a config from YAML or a JS object, strip out // and /* */ lines before validating.

Unquoted object keys

{name: "Alice"} parses in JavaScript but not in JSON. Every key must be wrapped in double quotes.

NaN and Infinity

JSON only represents finite decimal numbers. NaN, Infinity and values that overflow to them are rejected, often at a position that looks like a perfectly good number.

Technical Details

Validation uses the browser's native JSON.parse, the same engine that runs in every modern browser. That means the verdict matches what your own code will see when it calls JSON.parse.

The error position is derived from the character offset the parser reports, then converted into a 1-based line and column. The column counts characters, not bytes, so UTF-8 text does not shift the reported position.

The plain-English explanation is a heuristic pass over the characters around the error offset. It is conservative: when the cause is not obvious, it falls back to a neutral description rather than guessing.

Validation is a single native parse, so there is no streaming or chunking and no practical limit below the browser's memory ceiling. Documents in the hundreds of kilobytes validate in milliseconds.

Everything runs client-side. The document is read and parsed in memory and nothing is transmitted, which makes the validator safe for payloads that contain secrets.

Frequently Asked Questions

Does valid JSON always mean the data is correct?

No. Validation checks syntax, not meaning. A document can be perfectly well-formed yet contain a value you did not expect - a string where a number should be, or an empty object where you expected data. Validation only guarantees the parser can read it.

What is the difference between this and JSON Formatter?

The validator reports whether a document parses and where the first error is. The formatter beautifies and minifies a document. They are complementary: validate first to make sure a document is sound, then format it for reading.

Why does my browser accept this but the validator rejects it?

A common cause is a JSON5 or JavaScript-style feature - comments, single quotes or trailing commas - that your own tooling strips out before parsing. JSON.parse is strict, and the validator uses the same strict grammar.

Is my JSON uploaded anywhere?

No. Validation runs entirely in your browser. Nothing is sent to a server, stored or logged.

Can it validate very large files?

Within your browser's memory limits, yes. Validation is a single native parse pass, so even multi-megabyte documents usually validate instantly.

Why does my backend reject JSON that this validator accepts?

Different parsers enforce subtly different things: some reject a byte-order mark at the start of a file, some are stricter about duplicate keys, and older libraries are stricter about nesting depth or extremely large numbers. When a backend disagrees, check the edges of the document for invisible characters and compare against the strictest parser you have.

Data & Privacy

Your data stays in your browser. Nothing is uploaded.

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