Regex tester

Type regex (or re with a space) to open the editor. You can pre-fill it: re /(\w+)=(\d+)/g a=1, b=2.

In the editor

• A pattern box and flag toggles (g i m s u y). Hover a flag to see what it means.
• A test text box.
• Live results: the text highlighted with each match, and a table of positions, matches and capture groups (numbered and named).
• An optional Replace preview with $1, $<name> and so on.
• Ctrl+Enter (or Copy) copies /pattern/flags, with slashes escaped so it pastes straight into code.

Spaces, tabs and line breaks in matches are shown as ·, → and ↵. The match count caps at 500, and the table lists the first 100.

Slow patterns can’t freeze the page

Matching runs in a background worker with a 1.5 second limit. A pattern with catastrophic backtracking, such as (a+)+$ on a long string, shows a warning instead of locking up the page.

Copied regexes are saved in Recent and reopen with their pattern, flags and test text.