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JSON Validation

JSON Validator

JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules. Essential for developers catching malformed payloads before integration, validating API responses, and debugging configuration file syntax errors.

JSON format and quality

In brief

JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules.

Reviewed: 2026-09-18

What this tool supports

  • Instant JSON validation
  • Syntax error detection
  • Line number highlighting
  • Detailed error messages
  • Works offline
  • No data uploads
  • Supports large files
  • Free to use
  • JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules.
  • Use {"active": tru} as the local source.

How to Use JSON Validator

Validate your JSON data and find syntax errors with this browser-based tool.

  • Step 1

    Paste your JSON

    Copy your JSON and paste it into the input area.

  • Step 2

    Review validation

    The tool automatically validates and shows any errors.

  • Step 3

    Check error details

    Error messages include line numbers and descriptions.

  • Step 4

    Fix the errors

    Correct the highlighted issues in your JSON.

  • Step 5

    Use supported input

    Start with {"active": tru}.

  • Step 6

    Choose relevant options

    JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules.

Common mistakes

Validating minified JSON without checking for hidden syntax errors

Consequence: Minified JSON can hide trailing commas or missing quotes that only surface in strict mode.

Fix: Paste the raw JSON and let the validator check every character against RFC 8259.

Assuming valid syntax means valid data schema

Consequence: JSON can be syntactically correct but contain wrong types, missing required fields, or invalid values.

Fix: Use JSON Schema validation separately for business rule checking beyond syntax.

Ignoring BOM or invisible characters in pasted JSON

Consequence: Byte order marks and zero-width spaces from copy-paste can cause parse failures.

Fix: If validation fails unexpectedly, try re-typing the JSON manually or use a hex editor to check for invisible characters.

Best practices

  • Fix errors in reported order — JSON parsers stop at the first syntax break, so later line numbers shift after each correction.
  • Distinguish syntax validity from schema conformance: passing validation confirms RFC 8259 syntax, not required fields or value formats.
  • Check for invisible characters when a document looks valid but fails — copied text can carry zero-width spaces and non-breaking spaces that break parsing.
  • Validate before minifying, converting, or sorting; every downstream tool assumes input that parsed successfully.

Connected workflows

Prepare and process

JSON Validator

JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules.

  1. Use supported input
  2. Choose relevant options
  3. Run locally
  4. Review diagnostics

Verify before integration

JSON Validator

Validate Syntax error near "tru" before another application uses it.

  1. Run locally
  2. Verify the result
  3. Copy, download, or continue

Continue through the tool family

JSON Validator

Correct the reported syntax position in the source, then run JSON Formatter to normalize the fixed document.

  1. Verify the result
  2. Copy, download, or continue

Browser limitations

  • Validating very large documents (multiple MB) parses the full structure in one pass; extremely large inputs are bounded by available tab memory.
  • Clipboard access requires browser permission and may be blocked in private browsing, iframes, or restricted security contexts.
  • Error positions reference the parsed text as provided; documents with mixed line endings report positions in the normalized text.

Authoritative resources

JSON.orgPublisher: json.org · Reviewed: 2026-09-18JSONLintPublisher: jsonlint.com · Reviewed: 2026-09-18RFC 8259: JSONPublisher: rfc-editor.org · Reviewed: 2026-09-18ECMA-404 JSON syntaxPublisher: ecma-international.org · Reviewed: 2026-09-18

Concrete examples

Input
{"active": tru}
Result
Syntax error near "tru"

This example verifies JSON Validator's primary behavior without uploading data.

Frequently asked questions

What is JSON Validator?

JSON Validator checks your JSON data for syntax errors and highlights issues with line numbers.

Does JSON Validator upload my data?

The validator checks for syntax errors like missing commas, unclosed brackets, trailing commas, and invalid escape sequences in your JSON.

How do I validate JSON?

Each error includes the exact line and column number, a description of the problem, and suggestions for how to fix it.

Can I fix errors automatically?

The validator highlights errors but does not auto-fix them. You must fix them manually.

What types of JSON syntax errors are caught?

The validator catches missing commas, unclosed brackets, trailing commas, invalid escape sequences, duplicate keys, NaN/Infinity literals, single quotes instead of double quotes, and comments in JSON.

What JSON validation errors does the tool detect?

The validator catches syntax errors (missing commas, unclosed brackets, trailing commas), structural issues (duplicate keys, invalid escape sequences), type problems (NaN and Infinity literals), and encoding issues. Each error includes the line and column number for quick debugging.

Can I copy the validated output?

The validator catches common mistakes including duplicate keys, NaN/Infinity literals, single quotes instead of double quotes, and comments in JSON.

What types of JSON errors does the tool detect?

The tool detects syntax errors (missing quotes, trailing commas, wrong brackets), type errors, encoding issues, and structural problems. Error positions include line and column numbers.

What does JSON Validator do?

JSON Validator parses the supplied text and reports JSON syntax failures locally; it does not apply JSON Schema or application business rules.

What is a concrete JSON Validator example?

Yes. The validator processes everything locally in your browser. No JSON data is sent to any server during validation.

Privacy and offline behavior

JSON Validator processes input and produces output inside this browser. The tool does not upload tool data. Browser capabilities such as files, clipboard, camera, Canvas, Web Crypto, workers, or downloads are used only after the workflow or an explicit user action requires them.