Encode and decode Base64, base64url and MIME with UTF-8-safe text for Arabic and emoji
Regex Tester
Test JavaScript regular expressions with the d, g, i, m, s, u, v and y flags, showing matches, positions and named groups with a replace preview, inside a Worker with a timeout that prevents freezing.
Workspace
Replace result
How the result is calculated
The expression runs in the JavaScript engine (RegExp) inside a Web Worker with a 1.5-second timeout; if it overruns (catastrophic backtracking such as (a+)+$) the Worker is terminated so the page does not freeze. Every match is shown with its position and numbered and named groups, plus a replace preview with the selected flags. The text limit is 200,000 characters.
Limits:
The engine is JavaScript: some PCRE, Python and Go features (possessive quantifiers, inline
(?i), atomic groups) are unsupported or behave differently. The timeout protects the page but does not fix the expression. No code generation for other languages and no visual explanation.FAQ
Why does my expression time out?
It may contain catastrophic backtracking like (a+)+; simplify it or bound the repetition.
How do I use named groups?
Write (?<name>…); they appear under named, and use $<name> in the replacement.
