Frequently asked questions
- Is my data uploaded to a server?
- No. Every operation runs inside your browser using JavaScript. Nothing you paste or type is sent to our servers, stored or logged. You can disconnect from the network after the page loads and the tool keeps working.
- Which flavour of regular expression is this?
- JavaScript's, because it runs in your browser. It is close to PCRE for everyday patterns; the differences appear in lookbehind, recursion and some Unicode property escapes.
- Why is my pattern so slow?
- Almost certainly catastrophic backtracking - nested quantifiers such as (a+)+ against text that does not match can take exponential time. JavaScript cannot interrupt a running regular expression, so this caps the number of matches and the input size rather than pretending otherwise.
- Do I include the slashes?
- No. Write the pattern on its own and set the flags with the checkboxes.
Related tools
Stuck on an error?
Every common JSON parse error is explained separately, with the cause and the fix: common JSON errors.
How your data is handled
Everything happens on your device. There is no upload, no storage and no logging, and only your interface preferences - theme, indentation, font size and word wrap - are kept between visits. Closing the tab clears the document.