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JSON Lint

Validate, format, and minify JSON instantly — all in your browser with zero data sent to any server.

1

Paste or Type JSON

Paste any raw JSON payload, API response, configuration file, or webhook data into the editor. You can also load our sample payload to test.

2

Validate & Fix Errors

Click Validate JSON. The tool instantly flags syntax violations—including trailing commas, unescaped quotes, and missing brackets—with line and column markers.

3

Prettify, Minify or Copy

Format your data with 2-space or 4-space indentation for debugging, or compress it with Minify for high-throughput production API calls.

Engineering Reference

Mastering JSON Syntax: Why APIs Break & How to Prevent Failures

JavaScript Object Notation (JSON, standardized under RFC 8259 and ECMA-404) is the universal lingua franca of modern web architecture, RESTful microservices, and CRM webhooks. Despite its simplicity, strict parser implementations in languages like Go, Python, Java, and PHP routinely reject payloads due to minor syntactic mistakes.

cancel Top JSON Syntax Violations

  • Trailing Commas: Adding a comma after the final object property or array element ([1, 2,]) is forbidden in RFC 8259.
  • Single Quotes: JSON keys and strings must strictly use double quotation marks ("key": "val"), never single quotes.
  • Unquoted Object Keys: Unlike JavaScript objects, every key in JSON must be wrapped in double quotes.
  • Unescaped Control Characters: Unescaped line breaks, tabs, or backslashes within string values trigger instantaneous parser termination.

check_circle Production Payload Best Practices

  • Minify for Transport: Strip whitespace, tabs, and indentation to reduce packet size by 20% to 45% on high-volume webhook endpoints.
  • Strict Type Coercion: Never pass numbers or booleans as quoted strings unless preserving arbitrary-precision 64-bit integer IDs.
  • UTF-8 Encoding: Always serialize strings in UTF-8 without byte order marks (BOM) to ensure cross-platform compatibility.
  • Automate Validation: Validate JSON payloads in your CI/CD pipelines before sending webhooks to Salesforce, HubSpot, or custom APIs.

Frequently Asked Questions

How does the online JSON linter and validator work? expand_more

The tool uses JavaScript's native JSON parser with custom error pinpointing. It highlights syntax errors, line numbers, and character positions, allowing you to format, prettify (2-space or 4-space), or minify JSON payloads with instant real-time feedback.

Why does JSON validation fail on trailing commas? expand_more

The RFC 8259 JSON standard strictly forbids trailing commas after the last item in an array or object. While modern JavaScript engines permit trailing commas in object literals, strict JSON parsers will fail. Our validator pinpoints exact trailing comma locations so you can fix them.

Is my JSON payload kept private and confidential? expand_more

Yes. All validation, linting, formatting, and syntax highlighting execute 100% locally in your client web browser. No data, API keys, customer records, or payload bodies are ever transmitted to our servers or third parties.

Can I minify JSON for API payload optimization? expand_more

Yes. Clicking Minify strips all extraneous whitespace, line feeds, and indentation while preserving syntactic integrity. This reduces payload size significantly for high-speed network transmission and serverless execution.

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