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JSON Validator

Validate JSON syntax instantly in your browser. Catch parse errors with line and column hints, inspect structure stats, and export a validation report - no upload required.

JSON Input

Paste JSON to check syntax and inspect structure stats.

No JSON yet

Paste JSON above or load the example to validate syntax.

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Developer
Version
1.0.0

Key Features

  • Instant syntax check

    Paste JSON and get an immediate valid or invalid result using the same rules as JSON.parse.

  • Line and column hints

    When a parse error includes a position, the tool highlights the approximate line and column so you can fix issues faster.

  • Structure insights

    Valid documents show root type, size, nesting depth, key counts, and a pretty-printed preview you can copy or download.

How to Use

  1. 1

    Paste your JSON

    Copy JSON from an API response, config file, webhook payload, or log snippet into the editor.

  2. 2

    Review the result

    See whether the document is valid. Invalid input shows an error message; valid input shows structure stats and a formatted preview.

  3. 3

    Copy or download

    Export a validation report, or copy the pretty-printed JSON for use in docs, tickets, or tests.

Use Cases

  • Debugging a failed API integration

    Paste a webhook or API response that a service rejected as malformed and pinpoint the exact character causing the failure.

  • Checking hand-edited config files

    Validate a JSON config file after manual edits to catch trailing commas or unquoted keys before deploying it.

  • Verifying a clipboard paste is complete

    Confirm that JSON copied from a chat, ticket, or log was not truncated or corrupted before you rely on it.

  • Reviewing nested payload structure

    Check the nesting depth and key counts of a large configuration or API response before deciding how to process it further.

Examples

Valid API payload

Confirm a response body is parseable before consuming it.

{"status":"ok","count":3}
Valid JSON · root type: object · top-level keys: 2

Trailing comma error

Catch a common hand-edited JSON mistake.

{"items":[1,2,],}
Invalid JSON with a syntax error near the trailing comma

Nested config file

Inspect nesting depth and property volume for large configs.

{"app":{"db":{"host":"localhost","port":5432}}}
Valid JSON · nesting depth reported with structure stats

Benefits

  • Catch broken JSON before it reaches production
  • Debug API and webhook payloads in seconds
  • Share a clear pass/fail report with teammates
  • Keep sensitive payloads on your device
  • Pair validation with formatting for cleaner diffs

Best Practices

  • Validate first, then beautify - fixing syntax is harder after aggressive reformatting of invalid text.
  • Treat JavaScript object literals and JSON as different languages: no trailing commas, single quotes, or comments in JSON.
  • For contract checks (required fields and types), use a JSON Schema validator in addition to this syntax check.
  • When pasting from logs, strip surrounding non-JSON text such as prefixes, timestamps, or truncated endings.

Common Mistakes

  • Leaving a trailing comma after the last object property or array item.
  • Using single quotes or unquoted keys, which are valid in JavaScript but invalid in JSON.
  • Assuming a successful parse means the payload matches your API schema.
  • Pasting incomplete streamed chunks that cut mid-string or mid-object.

Privacy Notice

All validation and pretty-printing run in your browser with the built-in JSON parser. ToolMint does not upload, store, or transmit the JSON you paste. After the page has loaded, you can continue validating offline.

About This Tool

What is this tool?

A JSON Validator is a developer utility that checks whether text follows the JSON data interchange format. It parses input using standard JSON rules and reports success or a syntax error. ToolMint’s JSON Validator also surfaces structure stats for valid documents - root type, character count, nesting depth, and key or item counts - so you can inspect payloads while confirming they parse correctly. Unlike a schema validator, a syntax validator answers one question first: can this text be parsed as JSON at all?

Why use it?

Invalid JSON breaks APIs, config loaders, CI pipelines, and frontend state hydration. A fast browser-based validator helps you spot missing braces, bad commas, and quote mistakes before you commit, deploy, or file a bug. Because processing stays local, you can validate private customer payloads, auth-adjacent config, and staging responses without uploading them to a third-party service. Clear line and column hints reduce the time spent hunting for a single bad character in a long document.

Limitations

This tool validates JSON syntax only. It does not enforce JSON Schema, OpenAPI contracts, semantic types beyond what JSON.parse accepts, or duplicate-key policies used by some stricter parsers. Extremely large documents may be slow or memory-intensive because parsing happens entirely in the browser. The tool does not repair invalid JSON automatically - it reports the failure so you can fix the source.

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