Regex Tester
Test and debug regular expressions instantly in your browser. Live match highlighting, group captures, flag toggles, and quick patterns — all free and private.
🔍 Regex Tester
🎯 Matches
📦 Captured Groups
📋 How to Use the Regex Tester
- 1Enter Your Pattern: Type your regular expression in the Pattern field. Omit surrounding slashes — enter only the raw pattern text.
- 2Toggle Flags: Click the flag buttons to enable or disable g (global), i (case insensitive), m (multiline), s (dotAll), and u (unicode) as needed.
- 3Paste Your Test String: Type or paste the text you want to match against in the Test String box below the pattern.
- 4See Live Highlights: Matches are highlighted in alternating yellow and green directly in the test string area as you type.
- 5Review Match Details: The results panel shows total match count, first match position, all matched strings, and any captured group values.
- 6Use Quick Patterns: Click any Quick Pattern button to load a pre-built regex for common use cases like email, URL, Indian mobile number, and more.
⭐ Key Features
Live Match Highlighting
Matches are highlighted in real time as you type — alternating colors help distinguish overlapping or adjacent matches clearly.
Full Flag Support
Toggle g, i, m, s, and u flags individually with a click. The active flags display updates the pattern preview in real time.
Capture Group Display
All capturing groups — including named groups using (?<name>…) — are extracted and displayed separately in the groups panel.
Quick Pattern Library
Nine pre-built patterns for email, URL, IP address, Indian mobile, hex color, date, HTML tag, PIN/ZIP code, and whitespace.
Inline Error Reporting
Invalid regex syntax shows a clear error message with the exact reason — no cryptic browser console errors.
100% Private
All regex processing runs entirely in your browser using JavaScript's native RegExp engine. No data is sent to any server.
🧮 How the Regex Engine Works
/pattern/flags → JavaScript new RegExp(pattern, flags)Global Match:
string.matchAll(regex) → iterator of all match objectsMatch Object:
{ index, [0]: fullMatch, [1]: group1, groups: {named} }Highlighting: Matches replaced with
<mark> tags in mirrored display layerError handling:
try { new RegExp(p,f) } catch(e) { showError(e.message) }Common Regex Syntax Reference
| Token | Meaning | Example |
|---|---|---|
| . | Any character except newline | c.t → cat, cut, cot |
| \d | Any digit (0–9) | \d{3} → 123 |
| \w | Word character [a-zA-Z0-9_] | \w+ → hello_123 |
| \s | Whitespace (space, tab, newline) | \s+ → spaces |
| ^ | Start of string (or line with m flag) | ^Hello |
| $ | End of string (or line with m flag) | world$ |
| * | 0 or more of preceding token | ab* → a, ab, abb |
| + | 1 or more of preceding token | ab+ → ab, abb |
| ? | 0 or 1 of preceding token (optional) | colou?r → color, colour |
| {n,m} | Between n and m repetitions | \d{2,4} → 12, 123, 1234 |
| [abc] | Character class — matches a, b, or c | [aeiou] |
| [^abc] | Negated class — not a, b, or c | [^0-9] |
| (abc) | Capture group | (\d+)-(\w+) |
| (?<name>…) | Named capture group | (?<year>\d{4}) |
| (?:…) | Non-capturing group | (?:ab)+ |
| a|b | Alternation — a or b | cat|dog |
| \b | Word boundary | \bword\b |
| (?=…) | Positive lookahead | \d+(?= kg) |
| (?!…) | Negative lookahead | \d+(?! kg) |
📌 Practical Examples
🇮🇳 Example 1 — Validating Indian Mobile Numbers (Backend Team, Bengaluru)
A Bengaluru-based startup's backend team needed to validate Indian mobile numbers in form submissions. Indian numbers are 10 digits starting with 6, 7, 8, or 9. They used the pattern:
[6-9]\d{9} with the g flag
Test string: "Call us at 9845012345 or 011-23456789 or +91-7896541230" — correctly identifies 9845012345 and 7896541230 as valid Indian mobile numbers and excludes the landline.
🇮🇳 Example 2 — Extracting Order IDs from Log Files (E-commerce, Mumbai)
A Mumbai-based dropshipping company needed to extract order IDs in the format ORD-YYYYMMDD-XXXX from thousands of lines of server logs. Pattern used:
ORD-\d{8}-\d{4} with the g flag
Pasting 500 lines of logs returned 47 order ID matches instantly, with each result listed in the matches panel for copy-paste into their reporting sheet.
🌍 Example 3 — Scrubbing PII from Support Tickets (SaaS Company, UK)
A UK SaaS team used the regex tester to build and verify a pattern to detect email addresses in exported customer support tickets before sharing them with a third-party analytics vendor:
[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,} with gi flags
The tool's capture group display helped them confirm the domain portion was being isolated correctly before implementing the pattern in their Node.js script.
🇮🇳 Example 4 — Named Groups for Date Parsing (Developer, Pune)
A Pune developer parsing mixed date formats from a CSV export used named capture groups to extract year, month, and day separately:
(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})
The groups panel showed year: 2024, month: 07, day: 15 for each date match — confirming the pattern before integrating it into a Python data pipeline.
❓ What Is a Regex Tester?
A Regex Tester is an interactive tool that lets you write a regular expression pattern and immediately see which parts of a text string it matches. Instead of writing code, running it, and reading output in a terminal, you get visual feedback in real time — making it dramatically faster to develop, debug, and refine complex patterns.
Regular expressions (regex) are used by developers, data analysts, SEO professionals, and QA engineers for tasks like form validation, log file parsing, data extraction, search-and-replace operations, and text cleaning. The patterns can range from simple digit detection to multi-group, multi-flag expressions with lookaheads and named captures.
This tool uses JavaScript's native RegExp engine — the same engine that runs in Chrome, Firefox, Safari, and Node.js — so patterns you build here work directly in any JavaScript application without modification.
📖 Want a deeper guide to regular expressions — from basics to advanced patterns with real examples?
Read Our Full Guide: Regular Expressions Explained — A Practical Guide for Developers →❓ Frequently Asked Questions
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📬 Contact Us
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