Category: Developer
· URL: /tools/regex-checker.html
Tip: If you want all matches, enable g. The tool limits output to keep it fast.
Ready. Enter a pattern and text, then click Run.
Privacy: runs locally in your browser. No uploads, no tracking scripts.
How to use
Enter a pattern and some test text, then run the checker.
- Type your regex in Pattern (without surrounding slashes).
- Select flags (like g for all matches, i for case-insensitive).
- Paste your text into Test text.
- Click Run to see matches, indices, and groups.
- Optional: enter a Replacement to preview
text.replace()output.
Keywords this page targets (natural cluster): regex checker, regex checker online, regex tester, regular expression tester, validate regex pattern, regex syntax checker, test regex against text, regex match finder, regex flags tester, javascript regex checker, regex capture groups tester, named groups regex tester, regex replace tester, multiline regex tester, case insensitive regex test, global match regex test, debug regex pattern, find all matches regex, regex validator tool, regex group extractor
Secondary intents covered: Check whether a regex pattern is valid (compiles without errors), Find all matches and their positions in the input text, Inspect capture groups and named group values, Test how flags (g/i/m/s/u/y) change results, Preview a replacement result before using it in code, Troubleshoot multiline anchors like ^ and $, Confirm why a pattern matches nothing, Verify behavior of zero-length matches
FAQ
Do I include the /slashes/ around my regex?
No—enter the pattern only. Use the flag checkboxes for g i m s u y.
Why do I only see one match?
Enable the g flag to collect all matches; otherwise JavaScript returns only the first match.
Does it show capture groups and named groups?
Yes—each match lists numbered groups, and named groups when your environment supports them.
Is this the same as PCRE/Python/.NET regex?
No—this tool uses JavaScript RegExp, so some syntax and features may differ from other engines.
Can I test replacements?
Yes—fill in Replacement to preview text.replace(regex, replacement) output.
Why is output truncated?
To keep the page fast, the tool caps matches and preview sizes; refine your pattern or reduce input length.
Why does my regex feel slow or freeze?
Some patterns can cause catastrophic backtracking on large inputs. Try simplifying the pattern or testing smaller text.