Regex Tester
Test your regular expressions with real-time matching, groups, and replace functionality.
📋 Matches:
✏️ Replace Result:
How to Use Regex Tester
Follow these simple steps to get the best results.
Enter regex pattern
Type your regular expression pattern with any flags (g, i, m) in the pattern field.
Input test string
Paste the text you want to test against your regex pattern in the test string area.
View matched results
See all matches highlighted in real-time with capture group breakdowns and match positions.
Frequently Asked Questions
Everything you need to know about Regex Tester.
About the Regex Tester Tool
Test and debug your Regular Expressions in real-time with the ToolFlic Regex Tester. RegEx is famously powerful but often difficult to get right. Our tool provides a live environment where you can enter your pattern and test it against various strings, with instant visual feedback and capture-group highlighting.
Core Advantages
Save hours of frustration by testing your patterns before you implement them in your code. Our tester helps you understand exactly how your regex is matching (or not matching) your text, making it an essential learning and debugging tool for developers at all levels.
Architecture & Security
Built on the browsers native JavaScript RegExp engine, our tool provides an accurate representation of how your patterns will behave in a real-world web environment. It features a reactive UI that updates as you type, providing an instant feedback loop for your patterns.
Under the Hood: the Regex Tester explained properly
No marketing filler — just the mechanics, the trade-offs and the real limits, explained clearly.
How it actually works
The pattern and the flags are handed to the browser's own RegExp engine, the same JavaScript engine semantics you get in Node or in a <script> tag, so a match here is a match in your application. Five flags are exposed as checkboxes - g, i, m, s and u - and the results panel lists every match with its index, the captured text and any capture groups in order.
Testing is live: editing the pattern or the subject re-scans immediately. The replace field understands $1-style group references, so you can see the rewritten text beside the match list rather than discovering it in a console, and matched text is HTML-escaped before display so angle brackets in your subject show as characters instead of breaking the panel.
What that means for your results
Running on the real engine rather than a PCRE approximation is what makes this trustworthy for JavaScript work. What you see is literally what String.replace(), matchAll() and split() will do with the same arguments.
The u flag engages unicode mode, which changes how quantifiers and character classes treat surrogate pairs - useful when a pattern silently mis-slices emoji or non-Latin text, and a difference that is easy to miss without testing both ways.
Where it falls short — honestly
JavaScript regex is not PHP's PCRE. There is no \A or \Z anchor, no conditional subpatterns, no (?#comment) syntax, and named groups use the (?<name>…) form that older engines spell differently. Backslashes must also survive whatever language is embedding the pattern, so a regex that tests fine here can still need extra escaping inside a string literal.
Matching is unanchored unless the pattern says otherwise, and a globally-quantified subpattern over a very long subject can stall the tab, since nested quantifiers backtrack badly. The tool reports matches for the text you provide; it has no knowledge of the file format those matches came from.
A real end-to-end workflow
The productive loop is to paste a realistic sample rather than a toy string: an actual log line, the HTML attribute you want to grab, the CSV field with awkward quoting. Turn on m when ^ and $ should mean line boundaries, and turn on g when you expect more than one result, because the difference in the match list tells you immediately which you meant.
Build the pattern in pieces: match the smallest certain part, add one group, confirm the group list, then widen. Once it works, the replace panel shows the rewritten output before you touch your source. If the same text needs counting rather than matching, Word Counter and Character Counter give you the totals.
In-Depth Guides Using This Tool
Tested workflows, exact sizes and limits — written step by step by the ToolFlic team.
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