Runs locally in your browser. Nothing you enter is uploaded to our servers.
Result will appear here
Tips for testing regex
Test both matching and non-matching examples.
Watch catastrophic backtracking on user-controlled input.
Anchor patterns (^/$) when you mean a full-string match.
Document flags (i, m, s) your runtime will use.
Prefer simple patterns you can explain in a code review.
See what a regular expression actually matches
Processing stays in your browser — your input is not uploaded to our servers.
Paste a pattern and a sample string to highlight matches, groups, and misses. Flags like case-insensitivity change the result as much as the pattern.
A pattern that works in this JS-flavored tester may still differ in Python, grep, or .NET.
Test a regex
Enter the pattern and a sample
Use a realistic snippet from logs, not a single happy-path word.
Read matches and groups
Empty groups and greedy quantifiers are the usual surprises.
Tighten before shipping
Prefer explicit character classes over `.+` on untrusted input.
Regex tester FAQ
Which regex dialect is this?
JavaScript in the browser. Lookbehind and Unicode property escapes depend on the engine version.
Can a regex ReDoS my browser?
Pathological patterns can lock a tab. Keep samples small while you experiment.
Is the sample uploaded?
No. Matching is local.