What does Regex Tester do that other Developer pages on this site do not?

JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab. Short version: Test or replace with a JavaScript regex locally.

Does Regex Tester upload my file or text to Tool-You servers?

No. Regex Tester runs in this browser tab. Files stay on the device. Limit note: JavaScript RegExp only. Match or replace. Max 200 matches. Avoid catastrophic backtracking.

Should I use Text Diff instead of Regex Tester?

Use Regex Tester when you need Test or replace with a JavaScript regex locally. Use Text Diff when you need Compare two texts line by line, with ignore options. They share a category (Developer) but not the same job.

What are the limits of Regex Tester?

JavaScript RegExp only. Match or replace. Max 200 matches. Avoid catastrophic backtracking. Also: JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.

Regex Tester

Test or replace with a JavaScript regex locally.

JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.

What Regex Tester does

JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.

This URL is only for Regex Tester (developer · regex tester). Test or replace with a JavaScript regex locally. Other Developer tools on Tool-You look similar in the chrome, so the job definition below is the part that belongs to Regex Tester alone: JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.

How to use Regex Tester

Keep this tab on Regex Tester (/developer/regex-tester). Pasting into the wrong Developer tool (for example Text Diff) changes the job.
Paste or type the input Regex Tester expects. Path hint: developer · regex tester. Test or replace with a JavaScript regex locally.
Apply the Regex Tester action only. Word Counter is a different transform (Count words, characters, lines, and UTF-8 bytes.). JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.
Copy the output of Regex Tester if you need it elsewhere. Size/complexity still follows: JavaScript RegExp only. Match or replace. Max 200 matches. Avoid catastrophic backtracking.
If the text job is actually Compare two texts line by line, with ignore options., leave Regex Tester and open Text Diff.

When not to use Regex Tester

Skip Regex Tester when a neighbor tool matches better — start with Text Diff or Word Counter — or when the description already warns the job will fail. In the tool’s own words: JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.

Questions about Regex Tester

What does Regex Tester do that other Developer pages on this site do not?: JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab. Short version: Test or replace with a JavaScript regex locally.
Does Regex Tester upload my file or text to Tool-You servers?: No. Regex Tester runs in this browser tab. Files stay on the device. Limit note: JavaScript RegExp only. Match or replace. Max 200 matches. Avoid catastrophic backtracking.
Should I use Text Diff instead of Regex Tester?: Use Regex Tester when you need Test or replace with a JavaScript regex locally. Use Text Diff when you need Compare two texts line by line, with ignore options. They share a category (Developer) but not the same job.
What are the limits of Regex Tester?: JavaScript RegExp only. Match or replace. Max 200 matches. Avoid catastrophic backtracking. Also: JavaScript regex, not PCRE. Match list or replace with $1 / $& groups. Catastrophic backtracking can freeze the tab.