Regex Tester
Real-time regular expression testing and debugging with live highlighting
💡 Real-time matching · Supports named groups (?<name>) · Data is processed locally in your browser
About This Tool
Regular expressions are powerful pattern-matching tools used for text validation, search, and replacement. This free online regex tester provides real-time matching with live highlighting — type your pattern and see results instantly, no button clicking needed.
Use this tool to debug complex regex patterns before deploying them in production code, learn how different regex flags (global, case-insensitive, multiline, dotall) affect matching, test named capture groups, and experiment with Unicode property escapes.
It supports all major regex flags (g, i, m, s, u, y), real-time match highlighting with color-coded captures, and handles everything from simple email validation to complex multiline patterns. The debounced input ensures smooth performance even with large test strings.
How to Use
- Enter your pattern in the regex field and pick the flags you need.
- Type or paste the test text below it — matches highlight in real time.
- Toggle flags like global, case-insensitive or multiline to see how behavior changes.
- Named capture groups appear separately for quick reference.
Tip: If nothing matches, check whether a dot or star should be escaped with a backslash.
Common Mistakes
1. Unescaped metacharacters
Dots, stars, pluses and question marks are pattern operators. To match them literally, escape each one with a backslash — a bare dot matches any character.
2. Greedy overmatching
A greedy dot-star grabs as much as it can, often swallowing more than you intended across a line or document. Use the lazy variant to stop at the first closing tag.
3. Catastrophic backtracking
Nested quantifiers on overlapping character classes can freeze the regex engine on certain inputs. Simplify the pattern or add anchors to keep matching linear.
4. Forgetting the multiline flag
By default the caret and dollar signs anchor to the whole string only. With multiline text, enable the m flag so they anchor to each line.