KitJade
Developer ToolsRuns in your browser

JSON Validator

Pinpoint JSON errors by line and column, instantly.

Use the JSON Validator tool

Runs in your browserUpdated Report a problem

What this json validator does

JSON Validator checks whether a document follows the strict JSON grammar used by APIs, browsers and database engines. Unlike JavaScript, JSON forbids trailing commas, comments, single-quoted strings and unquoted keys — small differences that cause big production failures.

When a document fails, the validator shows the error text reported by the engine together with a line and column position, plus a short excerpt so you can jump straight to the problem. When it passes, you get structural statistics such as object depth and total key count.

Why use it

  • Verify a config or fixture file before committing it.
  • Check a webhook payload from a payment or messaging provider.
  • Confirm that generated JSON is syntactically valid before shipping it to a client.

How to use it

  1. 1Paste the JSON you want to check.
  2. 2Validation runs as you type, or press Validate for large documents.
  3. 3Read the status card: valid documents show size and structure; invalid ones show the location.
  4. 4Fix the highlighted issue and validate again.

Worked examples

Valid document

Input

[{"sku":"A-1","qty":3},{"sku":"B-7","qty":1}]

Output

Valid JSON · 2 objects · depth 3

Duplicate keys

Input

{"user":"a","user":"b"}

Output

Parses, but “user” is duplicated — most parsers keep the last value.

The JSON spec leaves duplicate keys undefined. Treat them as a bug and rename the fields.

Common mistakes

  • Using a trailing comma after the final array element.
  • Assuming valid syntax means valid semantics — types and required fields still need schema validation.
  • Ignoring duplicate keys because the parser accepts them.

Frequently asked questions

What is the difference between JSON validation and schema validation?
Syntax validation checks that the document can be parsed. Schema validation checks that the fields and types match a contract, such as a JSON Schema. This tool performs syntax validation and structure analysis.
Does the validator report duplicate keys?
Yes. Duplicate keys are syntactically legal but ambiguous, so the tool warns you when it finds them.
Can it validate JSON Lines (NDJSON)?
Not directly, because JSON Lines is a sequence of documents rather than one document. Validate one line at a time.

Related tools

All tools

JSON Formatter

Beautify or minify JSON, with precise error positions.

Runs locally

JWT Decoder

Read JWT claims and optionally verify HMAC signatures.

Runs locally

Hash Generator

MD5 and SHA digests for text or files, computed locally.

Runs locally

Base64 Encoder

UTF-8-safe Base64 encoding, including URL-safe mode.

Runs locally