Regex Tester
Write a pattern, paste your text, and see matches highlighted in real time. Supports all JavaScript RegExp flags and capture groups.
Test text
Matches
No matchesNo matches found
About Regex Tester
Regular expressions are one of the most powerful and most misunderstood tools in a developer's toolkit. They enable sophisticated text matching, extraction, and transformation in a single compact expression — but writing a regex correctly on the first attempt is rare. An interactive testing environment where you can see matches highlight in real time as you type is essential for developing accurate patterns efficiently.
Our Regex Tester uses JavaScript's native RegExp engine, matching the behavior you will get in Node.js, browser JavaScript, and any JavaScript-based toolchain. Type your pattern in the expression field, enter test text in the input panel, and watch all matches highlight immediately. Toggle the g (global), i (case-insensitive), m (multiline), s (dotAll), and u (unicode) flags to see exactly how they change the match behavior.
The match details panel lists every captured match — including the full match text, start and end index positions, and the values of all numbered and named capture groups. Named groups (`(?<name>...)`) are especially useful because they make your regex self-documenting and allow you to reference captured data by meaningful labels rather than indices. The built-in cheatsheet covers quantifiers, character classes, anchors, lookaheads, and group syntax for quick reference while building complex patterns.
How to Use Regex Tester
- 1Type your regular expression in the pattern field — no delimiters or slashes needed.
- 2Toggle the flags (g, i, m, s, u) you want to apply to the match operation.
- 3Paste or type your test text in the input area below the pattern.
- 4Matches highlight in real time — the match count and positions update as you type.
- 5Review the match details panel to inspect capture group values for each individual match.
- 6Consult the built-in cheatsheet using the reference button if you need syntax reminders.
Use Cases
- →Validate and test email, URL, phone number, or date format patterns before using them in code
- →Extract structured data — dates, IDs, prices, codes — from logs or raw text files
- →Debug a complex regex by building it incrementally and watching match behavior update
- →Learn regex syntax interactively by experimenting with patterns against real text samples
- →Test multiline patterns with the m flag against text blocks or log entries
- →Explore named capture groups for building self-documenting, maintainable regex patterns
Tips
- ✓Always use the g flag when you want to find all matches — without it, only the first match is returned
- ✓Named groups `(?<year>\d{4})` make captured data accessible by name, not index number
- ✓Use ^ and $ with the m flag to match line starts and ends rather than string boundaries
- ✓Lookaheads `(?=...)` and lookbehinds `(?<=...)` match context without including it in the capture
- ✓The cheatsheet tab covers all quantifiers, character classes, anchors, and group types
- ✓Test edge cases explicitly — what happens with empty strings, special characters, or Unicode?
Frequently Asked Questions
This tool uses JavaScript's built-in RegExp engine, which runs natively in your browser. It supports all standard ECMA-262 regex features including lookaheads, lookbehinds, named capture groups, and Unicode property escapes.
Each flag changes how the pattern is applied: g (global) finds all matches instead of just the first; i (case insensitive) makes A match a; m (multiline) makes ^ and $ match the start and end of each line; s (dotall) makes the dot (.) match newline characters.
Parentheses in a regex create capture groups. For example, (\d{4})-(\d{2})-(\d{2}) against "2024-06-15" captures three groups: "2024", "06", and "15".
Only text that matches your pattern gets highlighted in yellow. Non-matching text stays at its normal colour. If you see no highlights, the pattern has no matches in the current test text.
Greedy quantifiers (*, +, {n,m}) match as much text as possible. Lazy quantifiers (*?, +?, {n,m}?) match as little as possible.
Mostly yes. Most regex syntax is shared across languages. For JavaScript code specifically, results from this tool are a perfect match.