DEVELOPER / THE EVERYDAY TOOLKIT
Regular Expression Tester.
Test JavaScript patterns in a worker with an execution timeout. This is a free utility from my portfolio toolkit, with local browser processing and no account required.
Runs in an isolated worker with a one-second timeout. Supports g, i, m, s, u and y. Up to 1000 matches, 2000 pattern characters and 100,000 text characters.
SIMPLE BY DESIGN
How to use Regular Expression Tester
- Enter a JavaScript expression without slash delimiters and supply any supported flags.
- Paste representative text, including a few cases that should not match.
- Run the test and inspect indexes and capture groups; simplify patterns that hit the timeout.
Try a pattern with visible matches and a time limit.
Testing a regular expression against representative text helps reveal unwanted matches, missed cases and capture-group behavior. Enter the JavaScript pattern without surrounding slashes and select flags separately. Matching runs in a worker that is terminated after one second, reducing the risk of locking up the interface on expensive patterns. Results include each match, its JavaScript string index and capture groups. A successful test is not proof that a pattern safely validates all possible input.
A FEW THINGS TO KNOW
A little more clarity.
Why does a pattern time out?
Some patterns take excessive time on particular inputs. The worker is stopped after one second. Shorten the test or reduce ambiguous, nested repetition.
Is my input sent to a server?
No. This utility processes your input in your browser. URLs you paste are treated as data; the tool does not fetch them. Be careful with clipboard history on shared devices.
FROM THE JOURNAL
Use Regular Expressions for Focused Input Validation
Write small, testable patterns without treating a matching string as proof of a valid business operation.