SwiftCalcTools

Regex Tester — Regular Expression Tester & Debugger

Test and debug regular expressions online. Real-time regex matching with match highlighting and group capture visualization.

💻 Developer Tools ✅ Free

By SwiftCalcTools Editorial Team · Formula verified

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Preparing your calculator

How to Use Regex Tester

  1. 1Enter the required values in the input fields above.
  2. 2Click the Calculate button or results update instantly as you type.
  3. 3View your results in the output panel below the inputs.
  4. 4Adjust any values to recalculate instantly.

Frequently Asked Questions

g (global): find all matches, not just the first. i (case-insensitive): A matches a. m (multiline): ^ and $ match line starts/ends, not just string start/end. s (dotAll): . matches newline \n (by default it doesn't). x (extended, not in JS): ignore whitespace for readability. In JavaScript, you can combine flags: /pattern/gim.
Email (basic): /[\w.-]+@[\w.-]+\.[a-z]{2,}/i. Phone (India): /[6-9]\d{9}/. URL: /https?:\/\/[\w-]+(\.[\w-]+)+[\S]*/i. Date (YYYY-MM-DD): /\d{4}-\d{2}-\d{2}/. IP address: /\b\d{1,3}(\.\d{1,3}){3}\b/. HTML tag: /<[^>]+>/g. Whitespace trim: /^\s+|\s+$/g. Word boundary: \b matches between word and non-word characters.
.* is greedy — it matches as many characters as possible. .*? is lazy (non-greedy) — it matches as few characters as possible. Example: on "start <b>bold</b> end", <.*> matches the whole <b>bold</b> (greedy). <.*?> matches just <b> (lazy, stops at first >). Use lazy quantifiers when you want the shortest possible match.
Parentheses () create capturing groups that capture the matched substring. \1 backreferences the first group. Example: /(\w+)\s+\1/ matches repeated words like "the the". (?:...) is a non-capturing group (groups without saving). Named groups: (?<name>...) lets you reference by name. Groups appear in the match result and are shown in this tester's match table.