Test a regular expression
The quick way to build a pattern: type, see what lights up, check the group table, adjust. There is no button to press — the result updates as you type.
- Runs entirely in your browser
- Works offline
- No upload
- No sign-up
- No watermark
Loading the tool…
How it works
- Type the pattern and tick the flags you need (options such as “ignore case”).
- Paste the text you want to search. Matches are highlighted as you type.
- Read the table of captured parts, or type a replacement to preview the result of a find-and-replace.
Why nothing is uploaded
Every operation on this page is done by code running inside your browser tab, using the same engine that renders web pages. The file is read from disk into your tab’s memory, transformed there, and written back out as a download. It is never sent anywhere — not to us, not to a third party.
Verify it yourself
- Open your browser’s developer tools (F12) and select the Network tab.
- Load your file and run the tool.
- The only requests you will see fetch the tool’s own code — and, for a few heavy tools, their open-source engine from a public CDN — plus one small page-view ping to loreatec.jp (page address and title, nothing more). None of them carry your file.
Frequently asked questions
Which regex flavour (dialect) is this?
JavaScript’s — the engine built into every browser and into Node. Lookahead, lookbehind and named groups all work. If your pattern is meant for Python or PCRE, the basics carry over, but check it there too: possessive quantifiers and recursion do not exist here.
What do the group columns mean?
Each pair of capturing parentheses in your pattern becomes a numbered column — $1, $2 — and named groups show their names. If a group took no part in a match, the cell shows a dash. That is different from a group that matched an empty string.
Why does my pattern hang other testers but not this one?
A pattern that can match “nothing” at every position can loop forever. This tester steps past empty matches and caps the total number of matches, so a broken pattern shows its odd result instead of freezing the tab.
Is my test text sent anywhere?
No. People often paste production logs and customer data into regex testers without thinking. Here the matching runs entirely in this browser tab, so nothing leaves your computer.