Regex Tester: Test & Debug Regular Expressions Online
Test regex and inspect matches in your browser. Your pattern and test text are not uploaded to JW Tool Box; the site separately collects usage information as described in the Privacy Policy.
Test regex patterns, see matches highlighted in real time, and debug regular expressions — all in your browser.
Free online regex tester — test regex patterns against sample text, toggle flags, inspect matches and capture groups in real time. Runs locally in your browser, so your test data stays private.
How this page is maintained
- Steps and copy are checked against the current tool behavior.
- Browser limits, file-size constraints, or compatibility gaps are documented when relevant.
- Unless a page explicitly says otherwise, files and text stay in the browser during processing.
Free Online Regex Tester & Debugger
Test your regular expressions against real text and see matches highlighted instantly. Whether you're validating emails, parsing log files, extracting data from HTML, or debugging a stubborn pattern, this regex tester gives you immediate visual feedback without leaving your browser.
If you searched for a regex checker, test regex online, or a regular expression debugger, this page is built for that exact feedback loop: type the pattern, type the test text, and see the matches immediately.
Real-Time Validation Loop
As you type your pattern, the interface instantly evaluates the payload, highlighting positive matches, extracting capture groups, and visually exposing greedy quantifiers that might unintentionally swallow your entire document. No more guessing—see exactly what your regex matches (and what it misses) on every keystroke.
Built-In Starter Patterns
Not sure where to start? One-click presets cover the most common regex patterns: email addresses, phone numbers, IPv4 addresses, hex color codes, and invoice IDs. Load a starter, then customize it for your specific use case.
Browser Engine and Limits
The tool uses your current browser's native JavaScript RegExp engine. Controls expose g, i, m, s, and u; highlighting adds g internally to collect all matches. Engine versions and supported syntax vary, so test again in your deployment runtime. There is no execution timeout: avoid large inputs with nested, ambiguous quantifiers that can block the browser.
Your Data Stays Private
The regular expression and test text are evaluated in your browser and are not uploaded to JW Tool Box. The site separately collects usage information as described in the Privacy Policy. Follow your organization's rules when handling production or personal data.
Key features
- Instant highlighting: Matches and capture groups update as you type, so you can iterate without reloading.
- Flag toggles: Switch g, i, m, s, and u flags to test patterns in your current browser.
- Starter snippets: One-click patterns for emails, phone numbers, IP addresses, hex colors, and invoice IDs jumpstart testing.
Frequently asked questions
How do I test regex online?
Enter your pattern, paste sample text, and toggle flags like g, i, or m. Matches highlight instantly so you can debug the pattern before using it in code.
How do I see all matches?
The tester auto-enables the global flag when highlighting so every match is visible at once.
Which regex engine is used?
We use your browser's native JavaScript RegExp engine. Browser and runtime versions can support different features, so also test in your target environment.
What flags are supported?
The controls support g, i, m, s, and u. Sticky (y) and Unicode sets (v) are not offered. Highlighting collects all matches by adding g internally.
Is my text stored?
No. Everything runs client-side. Closing the tab clears your inputs.
Can it handle Unicode?
Yes. Enable the “u” flag to work with emoji, accented characters, and non-Latin scripts.
Related guides
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JavaScript Regex Debugger Guide: Capture Groups, Flags and Browser Limits
Use the JavaScript Regex Tester to inspect matched text, its index and numbered capture groups. This guide focuses on debugging behavior and browser limits. For your first test, use the basic regex walkthrough. Start with a small, reproducible example Enter the pattern without surrounding / characters. For an invoice identifier, use: regex
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How to Test Regex Online: A JavaScript Starter Walkthrough
To test a JavaScript regular expression online, open the Regex Tester, enter the pattern without / delimiters, and paste a short sample. The page highlights matches and lists their starting indexes and numbered capture groups. Use invented text while learning. Your first test: find an invoice number 1. Enter INV(\d{4})(\d{3}) in the pattern field. 2. Leave the default g and i flags enabled.