JSON Validator

JSON Validator & Lint Tool

The JSON Validator checks whether your JSON is valid and pinpoints errors with line and column details. It combines classic JSON validation with lint-style feedback, making it easy to find syntax issues quickly. Whether you are debugging an API response, preparing configuration files, or validating test fixtures, this tool helps you verify correctness in seconds. Everything runs locally in your browser, so your data stays private.

JSON is strict: keys must be in double quotes, trailing commas are not allowed, and strings must escape special characters. A single missing comma or mismatched bracket can break your payload. This validator highlights exactly where the parser fails, which saves time compared to manual inspection. It is also useful for linting large JSON files, where simple mistakes are hard to see.

What this tool checks

• Syntax validity: Ensures your JSON is well-formed.
• Line and column errors: Shows the exact location of parse failures.
• Escaping rules: Detects invalid escape sequences.
• Structure correctness: Confirms brackets, braces, and quotes are balanced.

How to use the JSON Validator

1. Paste JSON into the left editor.
2. Click Validate to run the checker.
3. Read the error message and fix the highlighted line/column.
4. Use Format or Minify if you want a cleaner output.

Example: invalid JSON

{
  "name": "Alice",
  "age": 25,
}

The trailing comma after 25 makes this invalid. The validator reports an error near that position.

Example: invalid quotes

{
  'name': 'Avi'
}

JSON requires double quotes. Replace single quotes with double quotes to validate successfully.

Lint-style feedback

Linting is about giving actionable feedback with precise location. This tool reports line and column so you can jump directly to the error. It is especially helpful for large payloads, where the mistake may be far from the visible error message.

Common errors and fixes

• Trailing commas: Remove trailing commas after the last item in objects or arrays.
• Single quotes: Replace with double quotes for keys and string values.
• Unescaped characters: Escape newlines, tabs, and quotes inside strings.
• Unmatched braces: Ensure every { has a matching } and every [ has a matching ].
• Unexpected tokens: Check for missing commas or extra characters between properties.

Best practices for valid JSON

• Format JSON before validating to spot errors faster.
• Validate early in your workflow, not just at the end.
• Keep JSON examples in version control to track changes.
• Need to analyze json size after validation? Check payload weight quickly.
• Use schema validation for strict rules beyond syntax.

Linting tips for large files

When validating large JSON files, the first error may hide other issues. Fix the earliest error, then revalidate. Repeat until the file validates cleanly. Use the line and column indicators to jump directly to the error location, and consider formatting the JSON to make the structure easier to read.

If you are working with logs or NDJSON, validate one object at a time. A single invalid line can cause the entire file to fail, so isolating the problematic line is often the fastest approach.

For repeated workflows, keep a small set of known-good samples to compare against, which makes it easier to spot structural changes.

Error patterns you will see

• Unexpected token: Usually a missing comma or an invalid character.
• Unexpected end of JSON: A missing closing brace or bracket.
• Invalid escape sequence: A backslash before an unsupported character.
• Unexpected number: A number where a comma or bracket was expected.

Validation workflow checklist

1. Paste JSON and run validation.
2. Fix the first reported error.
3. Re-run validation until clean.
4. Format or minify output as needed.
5. Validate against a schema if required.

Validator vs Linter vs Formatter

Validation checks correctness. Linting provides precise diagnostics. Formatting improves readability. This tool combines validation and lint-style diagnostics, while formatting is handled by the built-in format and minify actions or the dedicated JSON Formatter.

Validator vs Schema Validator

This tool validates syntax only. If you need to enforce required fields, types, or allowed values, use JSON Schema Validator. Combining both gives you reliable JSON that also matches your data contract.

Common JSON pitfalls

• Trailing commas: JSON does not allow trailing commas after the last element.
• Single quotes: JSON strings must use double quotes.
• Unescaped newlines: Line breaks inside strings must be escaped as \\n.
• Invalid numbers: Leading zeros and NaN/Infinity are not valid JSON.
• Comments: JSON does not allow comments, even though some parsers do.

Example: escaping strings

Input:

{
  "message": "Line 1
Line 2"
}

Fix by escaping the newline:

{
  "message": "Line 1\\nLine 2"
}

Checklist for clean JSON

1. Ensure all keys and string values use double quotes.
2. Remove trailing commas from arrays and objects.
3. Escape special characters in strings.
4. Validate and format for readability.
5. Validate against a schema if your API requires strict rules.

Use cases

API debugging: Validate responses or request payloads before sending.

Config files: Ensure JSON configs are correct before deployment.

Testing: Validate fixtures for automated tests.

Documentation: Check example JSON in docs and tutorials.

FAQs

Does this tool modify my JSON?
No. It only checks validity and reports errors.

Is my data uploaded?
No. All validation runs locally in your browser.

Can it validate large files?
Yes, but very large files may be slower in the browser.

Why does it say invalid when JSON looks correct?
Look for hidden issues like trailing commas, unescaped characters, or mismatched brackets.

Does it support comments?
No. Standard JSON does not allow comments.

How is linting different from validation?
Linting refers to the detailed, line/column feedback provided when validation fails.

What if I need strict field rules?
Use JSON Schema Validator for schema-based validation.

Can I format JSON here?
Yes. Use the Format and Minify buttons in the toolbar.

Can I validate JSON with trailing commas?
No. Standard JSON does not allow trailing commas.

Why do I get errors with Unicode?
Ensure Unicode escape sequences are valid 4-digit hex values.

Is validation the same as linting?
Linting emphasizes clear diagnostics, which this tool provides with line/column output.

Can I validate JSON from a URL?
Use Load JSON from URL to fetch data, then validate it here.