Free Online JavaScript Validator
JavaScript Validator checks your JavaScript code for syntax errors, formats minified code into readable structures, and provides a suite of conversion and analysis tools for everyday development work. We built six JavaScript utilities into one workspace so you can validate syntax, beautify code, minify files, convert JS objects to JSON, escape text for string literals, and analyze code metrics without installing software or creating an account. Paste your code into the editor, upload a file from your computer, or drag and drop it onto the workspace. Your code stays on your device because all processing happens locally in your browser.
JS Validator
Checks JavaScript syntax using the browser native parser and reports errors with messages, line numbers, and file metrics.
JS Formatter
Beautifies minified or unformatted JavaScript using js-beautify with 2-space, 4-space, and tab indentation options.
JS Minifier
Strips comments and collapses whitespace to reduce file size, showing real-time size comparison in the context bar.
JS to JSON
Converts JavaScript object literals to valid JSON, handling single quotes, unquoted keys, and trailing commas.
JS Escape
Escapes plain text for safe embedding in JavaScript strings, outputting double-quoted, single-quoted, and template literal formats.
JS Analyzer
Counts total lines, code lines, comments, functions, variables, classes, async calls, and file size in a metric dashboard.
Online JavaScript Validator for Catching Syntax Errors
A single syntax error in a JavaScript file can silently break an entire page or application. Our JavaScript Validator catches these errors before you deploy by running your code through the browser native JavaScript parser and reporting the exact error message, line number, and column position. The context bar at the top of the workspace shows a pulsing status indicator, validation state, and file statistics so you always know whether your code is clean. This real-time feedback loop means you can paste code, see results instantly, fix the problem, and paste again without waiting for build processes or server round trips.
Upload JavaScript Files From Your Computer
You can load JavaScript into the workspace three ways: paste it into the code editor on the left, drag and drop a file anywhere onto the workspace, or click the Upload File button in the toolbar. We accept .js, .jsx, .ts, .tsx, .mjs, .cjs, and .json files. Because everything runs in your browser, there is no upload size limit imposed by a server and your files never leave your machine. This makes the validator safe for proprietary code, production bundles, and files containing sensitive configuration data.
How JavaScript Syntax Validation Works
The validator passes your code to the browser JavaScript engine via the Function constructor. The engine attempts to parse the code and throws a SyntaxError if any part of the code is not valid JavaScript. This is the same parser that runs your code in production, so the result is authoritative. For valid code the tool reports line count, character count, and file size. If ES module syntax like import or export is detected, the tool notes that module-level validation has limitations since the Function constructor operates in script mode.
Format, Minify, and Convert JavaScript
Beyond validation, you often need to transform JavaScript code for different purposes. The JS Formatter expands minified code into clean, indented JavaScript using the js-beautify library with your choice of 2-space, 4-space, or tab indentation. The context bar shows a live indent mode selector so you can switch between formats and see the result update immediately. The JS Minifier reverses this process by stripping all comments and collapsing whitespace to produce compact code for production, displaying the original and output sizes with a percentage badge showing the reduction achieved.
Convert JavaScript Objects to JSON
The JS to JSON tool takes JavaScript object and array literals and converts them to valid JSON format. It handles common differences between JS notation and JSON: single quotes become double quotes, unquoted property keys get quoted, and trailing commas are removed. If regex-based conversion fails, it falls back to evaluating the expression through the Function constructor for maximum compatibility. The output appears in a syntax-highlighted code editor you can copy or download.
Escape Text and Analyze Code Metrics
The JS Escape tool takes plain text and escapes it for safe embedding inside JavaScript string literals. You get three output formats: double-quoted, single-quoted, and template literal, so you can pick whichever fits your coding style. The JS Analyzer counts total lines, code lines, blank lines, comment lines, function declarations, variable declarations, class definitions, async functions, and file size, displaying everything in a grid of metric cards for a quick codebase overview.
Your JavaScript Stays Private in Your Browser
We process everything locally using the browser JavaScript engine and the js-beautify library loaded from a CDN. No server requests, no cookies, no account required. You can safely validate production code, proprietary business logic, and configuration files containing API keys knowing that nothing is transmitted anywhere. Close the browser tab and your code is gone.
Related JavaScript and Code Tools
If you work with JavaScript regularly, these tools complement what you can do here:
- JS Beautifier -- format, beautify, minify, and validate JavaScript code
- JavaScript Compress -- compress and strip JavaScript for production
- JavaScript Obfuscator -- protect JavaScript with obfuscation
- JS Validator -- validate syntax, lint errors, and analyze code health
- JSON Formatter -- format, minify, validate, and transform JSON data
- HTML Formatter -- format and beautify HTML documents