How to use this tool
- Type your pattern and any flags (e.g. "gi" for global + case-insensitive).
- Paste or edit the test text — matches highlight live.
- Check the match list below for each match's full text and any capture groups.
Common mistakes to avoid
- Forgetting the g flag is the most common reason "only one match" shows up when you expected several.
- Remember JavaScript regex syntax differs slightly from PCRE/Python — e.g. lookbehind support and some escape sequences vary.
Why test regex in the browser?
This runs your pattern through JavaScript's own native RegExp engine — the exact engine your code will actually use if you're writing JavaScript, rather than a different regex flavor that might behave subtly differently.
Frequently asked questions
- Which flags are supported?
- Every flag JavaScript's RegExp supports: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode), and y (sticky). Enter them together, e.g. "gi".
- Why does my pattern only show one match?
- Without the g (global) flag, JavaScript's regex engine stops after the first match — add g to find every occurrence in the text.
- What are the numbered groups under each match?
- Capture groups from parentheses in your pattern — e.g. (\d+) captures a run of digits as group 1, shown as $1.
- Why does my pattern show an error?
- The error message is JavaScript's own RegExp constructor error, e.g. an unmatched parenthesis or an invalid flag combination — it points at exactly what's malformed.
How GetByteRush compares
Most free tools for this online work the same way: you upload your file to their server, wait, then download the result — which means your file (and often your email, for a "free" account) sits on someone else's infrastructure. Here's the actual difference:
| Feature | GetByteRush | Typical online regex testers |
|---|---|---|
| Regex engine | JavaScript native RegExp — matches your actual runtime | Varies — some use a different flavor (PCRE, etc.) |
| Data ever leaves your device | No — 100% client-side | Varies |
| Account required | Never | Sometimes |
("Typical online tools" reflects publicly documented behavior of common free file-processing sites as of 2026 — always check a specific competitor's own privacy policy and pricing page, since these details change.)