JSONLint
Validate and format JSON syntax with error highlighting. Quickly check your JSON for errors and beautify it.
Result
Please check your inputs.
How to Use This Tool
Paste or type your raw JSON code into the main text area of JSONLint.
Click the 'Validate' button to instantly check the syntax—any errors will be highlighted with line numbers and caret markers.
Review the error messages displayed below the editor; each points to the exact location and type of issue (e.g., unexpected token, missing comma).
To beautify your JSON, click the 'Format' button—this indents nested structures and aligns data for readability.
Copy the corrected or formatted JSON from the output box and use it in your project, or fix the errors manually based on the highlights.
What Is JSONLint?
JSONLint is a free online tool that validates and formats JSON (JavaScript Object Notation) data. It parses your JSON against the ECMA-404 standard and instantly reports any syntax errors, showing you exactly where and why the problem occurred. For developers working with APIs, configuration files, or data exchange, even a single missing bracket can break an entire application. JSONLint eliminates guesswork by providing clear, color-coded error highlights and line references. Beyond validation, it also beautifies messy or minified JSON into a clean, indented structure, making it easier to read, debug, and share. Whether you’re a beginner learning JSON or a seasoned engineer shipping production code, JSONLint saves time and prevents costly mistakes.
Formula
JSONLint uses a deterministic parsing algorithm based on the JSON grammar defined in RFC 7159 / ECMA-404. The process can be expressed as: Input JSON string → Lexer (tokenization) → Parser (stack-based state machine) → Error detection (error list with line:column) + Success → Formatter (recursive pretty‑print with configurable indentation). The 'variables' are: the raw JSON string (your input), a stack of opening brackets/braces to track nesting, a token stream that breaks the string into meaningful symbols (strings, numbers, booleans, null, delimiters), and an error accumulator that records any deviation from the grammar (like trailing commas, unescaped characters, or mismatched brackets). When no errors are found, the same token stream is passed to the formatter, which recursively outputs each token with proper line breaks and indentation.
Tips for Best Results
🧹 Always lint your JSON before committing to version control to catch hidden syntax errors that could break your build pipeline.
🔍 Pay special attention to trailing commas—they are invalid in JSON but often slip in from JavaScript object literals.
📋 Use the 'Minify' option (if available) or a separate minifier for production to reduce file size; JSONLint’s format shows the readable version.
🚀 For very large JSON files, paste a section at a time or use a command‑line alternative—JSONLint runs client‑side and may be slow on 10MB+ blobs.
Frequently Asked Questions
My JSON shows 'Unexpected token' – how do I fix it?
That error means the parser found a character it didn’t expect at a specific position. Look at the highlighted line and the caret: common causes are a missing comma between array elements, an unquoted key, or an extra closing brace. Double‑check the line above the caret for mismatched brackets or missing quotes.
Is JSONLint the same as a JSON formatter?
JSONLint acts as both a validator and a formatter. Its primary function is to check syntax and report errors, but it also includes a 'Format' button that beautifies your JSON with proper indentation. Unlike a pure formatter, it will refuse to format invalid JSON and instead show the error first.
Does JSONLint support JSON5 or comments in JSON?
No, JSONLint strictly follows the official JSON specification (RFC 7159). Comments, trailing commas, single‑quoted strings, and unquoted keys are not valid in standard JSON. For data that uses JSON5 or similar extensions, you would need a parser that explicitly supports those syntax rules.