Tools Viewer

JSON Validator

What Is a JSON Validator?

A JSON validator checks whether your JSON is written correctly. A missing comma, an unclosed bracket, single quotes, or an unquoted key can make JSON invalid and break an app or API request. A validator finds these problems and tells you where they are.

ToolsViewer's online JSON validator checks your JSON when you click Validate and shows a report with the error location, when one is available, plus extra warnings and hints.

How to Use the JSON Validator

Step 1: Add your JSON
Paste your JSON, import a .json or .txt file, fetch a public URL, or load the sample.

Step 2: Click Validate
The tool parses your JSON and checks the syntax.

Step 3: Read the result
The Result panel shows whether the JSON is valid. For invalid JSON, it shows the error message with the line and column when available.

Step 4: Fix the issue
Correct the problem and validate again. If a repair hint appears, you can open JSON Repair to fix common mistakes automatically.

JSON Validator Features

  • JSON syntax validation
  • Error messages with line and column when available
  • Hints for common mistakes, such as single quotes and unquoted keys
  • Warnings for duplicate keys
  • Warnings for numbers that may lose precision (unsafe integers)
  • A hint when a repaired version is available
  • Sample, Import, Fetch URL, and Validate options
  • Download the validation report
  • Send your JSON to related tools
  • Private processing in your browser

Common Uses

Check API payloads: Validate request and response bodies before sending them or while debugging.

Verify configuration files: Catch syntax errors in settings files before they cause problems.

Check copied JSON: Make sure JSON copied from logs, docs, or chat is valid.

Find duplicate keys: Spot repeated keys that can silently override each other.

Learn JSON syntax: See exactly what makes a JSON document invalid.

Supported Formats

  • JSON text
  • .json files
  • .txt files containing JSON
  • Public URLs
  • Output as a text validation report

This tool checks JSON syntax only. To check whether your data matches a set of rules, use the JSON Schema Validator.

Explore related tools like JSON Repair, JSON Schema Validator, and JSON Minifier to fix, check, and compress JSON online.