Aregex tester onlinelets you write a regular expression, paste your test text, and see matches highlighted in real time — without writing a single line of code. You get instant feedback on whether your pattern works and exactly what it captures.
Regex Visualizer is a free online regex tester that runs entirely in your browser. Nothing leaves your device. Paste your text, enter your pattern, and matches appear immediately as you type.
What does an online regex tester do?
An online regex tester takes a pattern and a piece of text and shows you:
- Which parts of the text match the pattern (highlighted inline)
- The content of each capturing group for every match
- How many matches the pattern finds in total
- Whether the pattern compiles without errors
Good tools also let you switch flags — global, case-insensitive, multiline — and see the results change immediately.
How to test a regex pattern online
- OpenRegex Visualizer.
- Type or paste yourregular expressioninto the pattern field. Do not include the surrounding slashes if the tool handles them for you.
- Paste the text you want to search into the test area below the pattern.
- Matches highlight as you type. Each match is outlined or colored so you can see exactly what the pattern found.
- Click any match to inspect the group captures — useful when your pattern has multiple capturing groups.
- Toggle flags like
g(find all matches) ori(ignore case) from the flag controls and watch the results update.
Common reasons a regex does not match
When your pattern matches nothing, the problem usually falls into one of these categories:
- Anchors in the wrong place:using
^and$makes the pattern match only the full string. Remove them if you want to find a match inside a longer text. - Missing global flag:without
g, the engine stops after the first match. Enable global mode to find every occurrence. - Special characters not escaped:characters like
.,(,[, and+have special meaning in regex. To match them literally, add a backslash:\.,\(. - Case mismatch:by default, most engines are case-sensitive.
hellodoes not matchHellounless you add theiflag. - Greedy quantifier consuming too much:
.*matches everything to the end of the line. Use.*?for a lazy match that stops as early as possible.
Testing email patterns — a common use case
Finding email addresses in text is one of the most common regex tasks. A good starting pattern is:
[a-zA-Z0-9._%+\\-]+@[a-zA-Z0-9.\\-]+\\.[a-zA-Z]{2,}
Steps to test it:
- Open the regex tester.
- Paste the pattern above into the pattern field.
- Set the
gflag and theiflag. - Paste a paragraph of text that contains email addresses.
- Every email address in the text highlights as a match. Check the results to make sure the pattern does not pick up anything it should not.
Testing date patterns
Date formats vary, so you usually need to test your pattern against real examples. To match dates in YYYY-MM-DD format:
\\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\\d|3[01])
Paste a few valid and invalid dates into the tester to confirm the pattern accepts the right values and rejects the wrong ones — such as month 13 or day 32.
Understanding group captures in the tester
Capturing groups, written as(pattern), store part of the match so you can use it separately. When the tester shows group results, each numbered group corresponds to a pair of parentheses in your pattern, from left to right.
Example pattern:
(\\d{4})-(\\d{2})-(\\d{2})
For the input2026-07-29, the tester reports:
- Group 1:
2026 - Group 2:
07 - Group 3:
29
Named groups, written as(?<year>\\d{4}), make the output easier to read in tools that support them.
Multiline mode explained
Without the multiline flagm, the anchors^and$match only the very start and end of the whole string. Enablemand they match the start and end of each line. This changes how many results the tester returns for multi-line input.
Toggle themflag in the tester while looking at a multi-line sample to see the difference right away.
Privacy when testing online
If your test text contains personal data — emails, names, user IDs — check that the tool runs locally in your browser and does not send anything to a server.Regex Visualizer processes everything on your device. No text you enter is ever uploaded.