Side-by-side line comparison.
Pretty-print, minify & validate JSON.
Built with privacy in mind. All processing happens entirely in your browser using open-source libraries.
A regex tester is a sandbox for writing and debugging regular expressions. You type a pattern, apply it to sample text, and instantly see every match highlighted, along with the capture groups the pattern produces. It is the fastest way to answer the developer’s eternal question: does this pattern actually do what I think it does?
Regular expressions are powerful and unforgiving. A pattern that works on one sample can silently fail on the next, and the difference between a correct expression and a broken one is often a single misplaced character or an off-by-one quantifier. Testing against real input, with visible matches and a count, turns that guesswork into a repeatable process. Being able to toggle flags like global, case-insensitive, multiline, and dot-all in real time also shows you how each flag changes behavior, which is how developers actually learn the quirks of the language.
This tester is built for instant feedback. There is no compile step and no round trip to a server — every keystroke updates the matches immediately, capture groups are broken out for inspection, and the match count confirms the result. Because all testing happens locally, you can safely work with private data, proprietary logs, or internal formats without them leaving your machine.
It is also an excellent teaching environment: build a pattern step by step, watch matches appear and disappear as you adjust each part, and use the flags to see how global or multiline changes the result. That hands-on feedback is how most developers finally internalize regex behavior.
Testing a pattern against one sample is rarely enough; the same expression must work across variations, such as different capitalization, optional whitespace, and edge-case inputs. This tester makes that easy by keeping the pattern, flags, and sample all editable on one screen, so you can iterate through cases in seconds and confirm the expression holds up before it reaches production code.
Who is it for? Developers validating patterns, data analysts cleaning text, QA engineers building assertions, and students learning regular expressions.
Regular expressions are the most compact way to express text rules, but their compactness is also their danger: a pattern is easy to write and easy to get subtly wrong. A tester gives you immediate, visible proof of what a pattern actually matches, which is the difference between shipping validation that works and discovering the bug in production.
It is also the fastest way to build confidence in a pattern before it touches real data. You can test against private logs, proprietary formats, or sensitive strings without uploading them anywhere, because everything runs in the browser. Combined with capture-group inspection and live flags, it turns regex debugging from guesswork into a repeatable process.
Yes, free with no signup or limits.
No. Testing happens locally in your browser.
No hard limit, though very long test text may slow older devices.
Yes, it works in mobile browsers.