When is a sample valid?
Valid means the pattern matches the whole sample, not only a slice of it. Invalid means it does not. Matches below still list every slice JavaScript finds.
JavaScript regex tester
The pattern runs in your browser with JavaScript RegExp. It is not PCRE2, and the pattern is not uploaded. Valid means the whole sample matches, not only a slice.
Questions
What do the flags do?
g finds every match, not only the first. i ignores letter case. m makes ^ and $ match at line edges. s lets the dot match newlines. u treats the pattern as Unicode.
Is this PCRE2?
No. This tester uses JavaScript RegExp in your browser. It is not PCRE2 and it is not regex101’s debugger.
Do I need an account?
No. There is no sign-in. You can paste more than two sample strings on this page.
Is the pattern uploaded?
No. The pattern, flags, and samples stay in your browser. Nothing is uploaded.