What it does
regex101 is an online regular-expression workspace with matching, substitution, extraction, unit tests, match details and several engine flavors.
Choose the destination regex flavor, enter sample text and inspect matches and captured groups. Keep both accepted and rejected examples in unit tests. Free access includes matching, two editable test strings, a single text or binary file, and a 50-event PCRE2 debugger preview. Pro adds longer traces, document and multi-file extraction, benchmarking and all converter targets; Free conversion targets JavaScript. The docs say editor operations run locally. Saving or publishing sends workspace fields to the service, while draft links contain editor content readable by recipients.
Strengths
- Several regex engine flavors
- Match details, captures and unit tests
Best for
- Checking a text extraction pattern before reuse
Sources
- regex101: Online Regex Tester, Builder, Converter & Debugger (Oct 26, 2026)
- regex101 Free and Pro controls (Oct 26, 2026)
- regex101 local operations versus saved/shared workspaces (Oct 26, 2026)