Match a pattern against sample input, with named captures highlighted and a flag dial.
The tools that come up when the actual job is interpreting data rather than collecting it: CSV viewer with column typing for the export you just got from the database, JSON formatter for the API response, regex tester against the source string, base64 for the binary blob someone embedded in a JSON field, hash for source verification, and the AI summarizer for digesting long-form sources.
Live match highlights as you type the pattern - so you can see whether the alternation does what you think it does.
Show / hide captures per group, including named captures. The group numbering is the same as JavaScript engines, so what you see is what your code will see.
Useful when a colleague hands you a "regex for X" pattern and you need to confirm what it actually matches before relying on it.
How to use it
Paste the sample input, then type the pattern. Matches are highlighted live as you type.
Toggle flags (i, g, m, s, u) and watch the match count update. The tool refuses invalid patterns with a clear error message at the line they fail.
Copy the pattern that matches your real-world strings, not the simplified ones you tested with.
JavaScript, including named groups, lookbehind and Unicode properties. PCRE-only syntax such as possessive quantifiers or atomic groups will not behave the same in a browser-based runtime.
Why does the pattern work here but not in my script?
Almost always the flags or the flavour: case-insensitivity, multiline anchors and the global flag all change what matches. Set the same flags in both places and test against the same sample.
Can I point it at a large log file?
Paste a representative sample to build and debug the pattern, then run it over the full file in your real pipeline. A tester is for shaping the expression, not for processing gigabytes.