Regex Tester
Test regular expressions live with real-time highlighting.
The concept of regex was invented by mathematician Stephen Kleene in 1951. Most developers still Google regex syntax every single time!
How to use the Regex Tester
Enter a regular expression pattern in the pattern field, set any flags (g for global, i for case-insensitive, m for multiline, s for dotAll), and paste your test string. Click Test to see all matches highlighted in real time. The match list shows every captured string. Use the quick-pattern buttons to instantly load common patterns like email, URL, or IP address matchers.
Step-by-step guide
- 1 Enter pattern
Type your regular expression pattern in the /pattern/ field. Use the flags input next to it for g, i, m, or s.
- 2 Paste test string
Paste or type the text you want to test against in the Test String area.
- 3 Click Test
Press ⚡ Test or press Enter in the pattern field. Matches are highlighted and listed below.
- 4 Use quick patterns
Click Email, URL, Numbers, Words, or IP to instantly load a common pattern and see it work.
What can you do with this tool?
- Debug and validate regular expressions during development
- Test email, URL, IP address, and phone number patterns
- Build and verify input validation patterns for forms
- Extract data from strings with capture groups
- Learn regex syntax with live feedback
- Test regex patterns before using them in JavaScript, Python, or Go
Why use STB's Regex Tester?
STB's Regex Tester is completely free — no account, no email, no credit card. It runs entirely in your browser so your data never leaves your device. Whether you're a developer, student, or just someone who needs a quick regex tester, open this tool and get results in seconds. No ads, no rate limits, no paywalls — just a fast, clean tool from Software That Benefits, a studio dedicated to free tools for developers and students.
Frequently Asked Questions
What regex flavor does this tool use?
This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. Most common patterns work the same across languages, but some advanced features like lookbehinds and named capture groups may behave slightly differently in Python, Java, or .NET.
What does the 'g' flag do?
The global (g) flag makes the regex find all matches in the test string instead of stopping at the first one. Without it, only the first match is returned. Always use g when you want to count or list all occurrences.
What is the difference between 'm' and 's' flags?
The multiline (m) flag makes ^ and $ match the start and end of each line, not just the whole string. The dotAll (s) flag makes the dot (.) match newline characters, which it normally skips.
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