Regex Tester
The Regex Tester lets you prototype and debug regular expressions against any text input in real time. Enter a JS-flavour pattern (without the surrounding slashes), set flags like g (global) and i (case-insensitive), paste your target text, and the tool lists every match with its zero-based index. Errors in your pattern produce a readable error message instead of a silent failure. A must-have for log parsing, form validation, scraping sed-style substitutions, and learning regex.
How to Use
To use the Regex Tester, simply open the tool page and interact with the controls in the panel above. The interactive panel handles input and produces instant results entirely in your browser — no signup, no upload. Use the Copy button when you want to transfer the output to your clipboard.
Key Features
- Runs in your browser — No data uploads or server roundtrips.
- Free & no signup — Use without registration or limits.
- Privacy first — Your input never leaves your device.
- Instant results — All processing is synchronous and local.
- Copy & download — Copy output or download to a file when supported.
Common Use Cases
This tool is useful for developers, designers, testers, students, and anyone who needs a quick, browser-based utility without installing software.
Tips & Tricks
Bookmark the tool for quick access during your workflow. Combine it with the related tools listed below for end-to-end productivity.
Frequently Asked Questions
Which regex flavour is used?
JavaScript ECMAScript flavour, the same engine your browser uses for string.match and regex.test.
What flags are supported?
All JS flags: g (global multiple matches), i (case-insensitive), m (multiline), s (dotall), u (Unicode), y (sticky).
Why does my pattern work differently than expected?
JS regex lacks some features of PCRE such as possessive quantifiers and named backreferences prior to ES2018.
Can I see capture groups?
Currently we show full matches. Captured groups can be inspected in the browser console using the same regex object.
Are large inputs slow?
Patterns without catastrophic backtracking are fast. Pattern complexity, not text size, is usually the bottleneck.