JSON Lint Online

Validate JSON syntax and find errors with precise line numbers — fast, private, browser-based

What Is JSON Linting?

JSON linting is the process of analyzing JSON text to detect syntax errors, structural problems, and deviations from the JSON specification (RFC 8259). A JSON linter parses the input and reports the exact location and nature of any errors — missing commas, unclosed brackets, trailing commas, single-quoted strings, unquoted keys, and other common mistakes that cause JSON parsers to fail.

Unlike simple validation that returns only pass or fail, linting provides actionable diagnostics: the line number, character position, and a description of what the parser expected versus what it found. This makes linting indispensable for debugging API responses, configuration files, data exports, and any JSON that was manually edited or generated by string concatenation rather than proper serialization. A good linter catches the errors that cost developers the most debugging time.

How to Lint JSON Online

1. Paste your JSON into the editor — the linter begins analyzing immediately as you type
2. Errors are highlighted inline with red markers at the exact position of each problem
3. Read the error message below the editor for a description of what went wrong
4. Fix the reported issues — the most common are trailing commas, missing quotes, and unclosed brackets
5. When all errors are resolved, the status indicator turns green confirming valid JSON

Why Use PinusX JSON Linter?

PinusX lints your JSON with 100% client-side processing — your data never leaves your browser. Every syntax check, error detection, and line number calculation happens locally in your browser tab. This matters because developers frequently lint JSON files containing database connection strings, API credentials, and infrastructure configurations. In November 2025, jsonformatter.org exposed over 80,000 user credentials that had been pasted into their server-based tool. PinusX prevents this by design: no data is transmitted, no server processes your input, and no logs are created. Your sensitive JSON configurations stay on your machine where they belong.

Frequently Asked Questions

What errors does the JSON linter detect?

The linter detects all JSON syntax errors including: trailing commas after the last element, single quotes instead of double quotes, unquoted property names, missing colons between keys and values, unclosed brackets or braces, duplicate keys in the same object, control characters in strings, invalid escape sequences, and non-standard values like undefined or NaN.

Does JSON allow trailing commas?

No. Unlike JavaScript, the JSON specification (RFC 8259) does not allow trailing commas after the last element in an array or object. A trailing comma like [1, 2, 3,] is invalid JSON and will be flagged by our linter. This is one of the most common JSON syntax errors.

Can I lint JSON with comments?

Standard JSON does not support comments. If your file uses JavaScript-style comments (// or /* */), the linter will flag them as syntax errors. For configuration files that need comments, consider using JSONC, JSON5, or YAML formats instead, which natively support comments.

What is the difference between JSON lint and JSON validate?

In practice they are very similar. Both check for valid JSON syntax. The term linting traditionally implies more detailed diagnostics — specific error messages, line numbers, suggestions for fixes — while validation may just return a boolean valid/invalid result. Our tool provides full linting with detailed diagnostics.

Can I lint very large JSON files?

Yes. The linter handles files up to several megabytes efficiently since all processing is local. For extremely large files, error detection focuses on the first error encountered since subsequent errors may be cascading effects of the initial problem.

Your data never leaves your browser. 100% client-side processing.