What regex flavor does this tool validate?
JavaScript regex (ECMAScript). This is the same engine used in Chrome, Firefox, Node.js, and Deno.
Regex Validator checks your regular expression for syntax errors before you use it in code. Invalid regex patterns crash JavaScript applications at runtime with uncaught SyntaxError exceptions — this tool catches those errors instantly. Paste your pattern, click validate, and see in milliseconds whether your regex is syntactically correct and will not throw in production.
The tool attempts to compile your pattern using JavaScript's built-in RegExp constructor. If the constructor throws a SyntaxError, the error message is displayed. If it succeeds, the pattern is confirmed valid. This is the same compilation step that runs when JavaScript evaluates a regex literal in your code.
JavaScript regex (ECMAScript). This is the same engine used in Chrome, Firefox, Node.js, and Deno.
Validation checks if the pattern itself is syntactically correct. Testing runs the pattern against sample text to see if it matches. Use the Regex Tester tool to also test against sample strings.
The validator uses the JavaScript engine. Most common patterns are compatible across JavaScript, Python, and PHP, but JavaScript-specific features like named groups (?<name>) may differ in other engines.
No. The tool runs entirely in your browser. Your pattern is never sent to any server.
Yes, completely free. No account required.
Unmatched parentheses, missing closing brackets in character classes, invalid escape sequences, and unclosed quantifiers (like {2 with no closing }).
Tool workspace
Free online regex validator — instantly check if a regular expression is valid JavaScript syntax. Catch regex errors before they cause runtime bugs. No login needed.
Input
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$Output
Valid regular expression