regex101
Test regular expressions in a selected engine, inspect explanations and capture groups, and preview text replacements.
Overview
regex101 puts a regular expression, test text, and match details in one workspace. You can compare highlighted matches with an explanation of the pattern and the values captured by each group.
The official engine guide lists JavaScript, PCRE2, Python, Go, and other options. Choose the engine that matches your application before refining a pattern. Similar syntax can behave differently.
Why it is useful
A successful match can still capture the wrong field. Inspect full matches, group names, and positions together, then use Substitution to preview the replacement text.
Good fit for
Developers testing extraction or validation patterns, people cleaning up text, and learners working with groups and quantifiers.
Try it when
In our JavaScript test, (?<item>[A-Z]+)-(?<id>\d+) matched ABC-123 and XYZ-42 but left no-match unselected. The details panel showed the separate item and id captures.
Entering $<item>:$<id> in Substitution produced ABC:123, no-match, and XYZ:42. Unmatched text stayed unchanged. Replacement syntax differs by engine; see the official substitution guide.
Before using it
Use anonymized samples, not credentials or personal data. Test the pattern again in your target runtime, especially for Unicode, escaping, and edge cases. We did not test other engines, saving or sharing, or advanced debugging features.
