Run the test to see matches and highlighted text.
Test JavaScript regular expressions and inspect matches directly in your browser.
Patterns run through the browser's own RegExp engine, so what matches here is exactly what matches in your code. Write the pattern body only — the delimiting slashes are implied, and the flags are set with the pills instead. Every match runs on a background thread with a one-second cutoff, so a pathological pattern (catastrophic backtracking) times out that one run instead of freezing the tab.
This uses native JavaScript (ECMAScript) regex semantics — the same engine your frontend or Node.js code runs. Most patterns port to PCRE/Python, but lookbehind support and escape rules can differ — test in the engine you actually deploy to.
g finds all matches instead of stopping at the first; i ignores case; m makes ^/$ match per line; s lets . also match newlines.
Most common causes: an unescaped special character (. + ? ( ) [ ]), or forgetting the g flag when expecting multiple matches.
Wrap part of your pattern in parentheses () — e.g. (\d{4})-(\d{2})-(\d{2}) captures year, month, and day as three separate groups.
Use the Regex Replace Tester for that — this tool focuses on matching and inspecting groups.
No — matching runs entirely in your browser.