Regex Tester
Test regular expressions in real time - enter a pattern and test strings, see matches highlighted with capture groups, and browse a built-in pattern library. All processing runs locally in your browser.
Test regular expressions in real time - enter a pattern and test strings, see matches highlighted with capture group details. All processing runs locally in your browser.
Why Use Our Regex Tester?
Real-Time Pattern Matching
See matches highlighted instantly as you type your regex pattern and test strings. Every modification to the pattern, flags, or test string updates the results immediately - no need to click a separate "test" button.
100% Private - No Data Upload
The regex tester runs entirely in your browser. Your patterns, test strings, flags, and matches never leave your device. No server uploads, no accounts, no tracking - your sensitive data stays completely private.
Full Regex Feature Support
Supports all standard regex flags (g, i, m, s, u, y), capturing groups with named group display, alternation, character classes, quantifiers, lookahead/lookbehind, and word boundaries. Works with any valid JavaScript RegExp pattern.
Built-In Pattern Library & Reference
Browse a library of 10 preset patterns (email, URL, phone, IP, dates, hex colors, and more) with ready-to-use test strings. An interactive quick reference table covers character classes, quantifiers, anchors, groups, and escape sequences.
Common Use Cases for Regex Testing
Web Development & Form Validation
Test and refine regex patterns for form validation - email addresses, phone numbers, ZIP codes, credit card numbers, and custom input formats. See exactly what matches and what doesn't before deploying to production code.
Learning & Teaching Regex
Students learning regular expressions can experiment with patterns and see immediate visual feedback. The quick reference table provides a handy guide to all major regex concepts while the preset library offers real-world examples to study.
Data Cleaning & Text Processing
Extract, validate, and transform data from CSV files, logs, or unstructured text. Use regex to find specific patterns (dates, IDs, URLs) in large text blocks, test the pattern iteratively, and then apply it in your data pipeline.
Debugging Complex Patterns
When a regex pattern doesn't work as expected, use the tester to isolate the issue. Test edge cases, empty strings, special characters, and boundary conditions. The capture group display helps debug group extraction issues.
Log Analysis & Monitoring
Parse server logs, application traces, and monitoring output using regex patterns. Test patterns against sample log entries to ensure they correctly extract timestamps, error codes, IP addresses, and other structured data from semi-structured logs.
Search & Replace Preparation
Before running a search-and-replace operation in your editor or IDE, use the regex tester to verify your pattern matches the intended text. Test the pattern against representative samples to avoid unintended replacements.
About the Regex Tester
Learn how regular expressions work, how our tester displays matches, and why browser-local processing keeps your data private.
What is a Regular Expression?
How the Tester Works
Understanding Regex Flags
Privacy & Security
Regex Tester FAQs
Everything you need to know about testing regular expressions with our free online tool.
What is a Regex Tester?
A regex tester is an interactive tool that lets you enter a regular expression pattern and a test string to see which parts of the text match. It displays matches in real time with visual highlighting, shows capture group details, and provides a quick reference for common regex syntax.
How do I enter a regular expression?
Type your regex pattern in the pattern input field (without delimiters - just the pattern). For example, to match email addresses, enter [a-z]+@[a-z]+\.[a-z]{2,}. Toggle the flag buttons (g, i, m, s, u, y) to modify how the pattern is applied. The forward slashes are shown automatically around the pattern.
What regex flags are supported?
All six JavaScript RegExp flags: g (global - find all matches, not just the first), i (case-insensitive), m (multiline - ^ and $ match line start/end), s (dotall - . matches newlines), u (unicode - treat pattern as Unicode), and y (sticky - match only from lastIndex). Click each flag button to toggle it on or off.
How are matches displayed?
Matching text segments are highlighted in yellow in the test string display. Below the highlighted text, a match summary shows the total match count and each match value. If your pattern contains capturing groups, each match expands to show the extracted group values labeled $1, $2, and so on.
Does the tool support capturing groups?
Yes. Any parentheses () in your pattern create capturing groups. The tester displays each captured group separately for every match, labeled $1, $2, etc. This is useful for extracting specific parts of matches, such as the username and domain from an email address.
What are the preset patterns for?
The preset patterns provide ready-to-use regex examples for common use cases: email, URL, phone numbers, IP addresses, ISO dates, hex colors, capitalized words, numbers, whitespace, and quoted text. Click a preset to load the pattern and a sample test string - great for learning or quick testing.
How do I use the quick reference?
Click the "Quick Reference" button to toggle the regex reference table. It covers character classes (\d, \w, \s), quantifiers (+, *, ?, {n,m}), anchors (^, $, \b), groups and lookahead, escapes, and character sets. Click any pattern in the reference to test it instantly.
Is my data safe?
Absolutely. The regex tester runs entirely in your browser using JavaScript's built-in RegExp engine. Your patterns and test strings are never sent to any server, stored, or logged. No accounts, no uploads, no tracking - your data stays completely private.
Can I copy my regex pattern?
Yes. Click the "Copy Pattern" button to copy the current regex pattern to your clipboard. The pattern is copied as a plain string (without delimiters or flags), ready to paste into your code, editor search bar, or other tools.
Is the Regex Tester free?
Yes - 100% free with no signup, no account, and no usage limits. Test unlimited regex patterns with as many test strings as you need. No ads, no paywalls, no hidden fees. Completely free forever.