About Regex Named Groups Tester
This page opens with a pattern that splits a log line into three named groups: level, service and message. A named group is written (?<name>...), and the table under the tester shows one column per name. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
The three sample lines give 3 matches, one per line. In code, the groups are on the match object as match.groups.level, match.groups.service and match.groups.message, which reads far better than match[1], match[2] and match[3].
Group names must be valid identifiers and unique within the pattern. Named groups are part of modern JavaScript and of many other languages, though the syntax differs a little between them.
How to use Regex Named Groups Tester
- Type or paste a regular expression into the pattern field, or pick one from the Try chips: email, URL, phone, date, IPv4 or hex colour.
- Toggle the flags you need: g for all matches, i to ignore case, m for multiline, s so the dot matches line breaks, u for Unicode and y for sticky.
- Paste your test text. Matches are highlighted as you type.
- Read the table under the tester for each match, its position, and its numbered and named groups.
- Switch to Replace to try a replacement string. Use $1, $2 and $<name> to reuse groups, then copy the result.
- Read "What the pattern means" to check the pattern does what you think.
Features
- JavaScript regex flavour with flags g, i, m, s, u and y.
- Live highlighted matches, with alternating colours so neighbouring matches stay distinct.
- Numbered and named capture groups in a table.
- Replace mode with $1, $<name> and $& in the replacement.
- A plain-English explanation of every token, with groups indented.
- A small pattern library with real test strings.
- Catastrophic backtracking protection: matching runs in a Web Worker and is stopped after a short time limit.
- Clear error messages for an invalid pattern.
Worked examples
(?<level>INFO|WARN|ERROR)\s+\[(?<service>\w+)\]\s+(?<message>.+) gives 3 matches with level, service and message
Each line yields the three named values in the table.
Privacy: how it works
- The pattern and the text are processed by code in this browser tab. Nothing is sent to Ulkaa or to any other server.
Tips
- Escape the special characters . * + ? ( ) [ ] { } ^ $ | \ with a backslash when you mean them literally.
- Prefer specific classes over the dot: [^"]* is faster and safer than .* when matching up to a quote.
- Anchor a validation pattern with ^ and $, or it will match a valid piece inside invalid text.
- Turn on the m flag when your text has several lines and you want ^ and $ per line.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial and no credit card. Ulkaa Tool does the work with your own device, so there is no server bill to pass on to you.
Do I need an account?
No. There is no sign-up and no login. Open the page and use it. An Ulkaa account is not needed for anything on this tool.
Does it run in my browser?
Yes. Your pattern and text are processed by code running in your browser tab, on your own device.
Is my data uploaded?
No. Your pattern and text are never sent to Ulkaa or to anyone else. You can check this yourself by watching the Network tab in your browser developer tools while you use the tool.
Do named groups still have numbers?
Yes. A named group is also numbered by position, so $1 and $<name> can refer to the same text.
More Regex Tester pages
- Regex TesterType a pattern and some text, and see every match, group and replacement as you type.
- Email Validation RegexCheck which lines look like an email address, and see why the others do not.
- URL Regex TesterFind web addresses in a block of text with a pattern you can edit.
- Phone Number Regex TesterMatch phone numbers written with brackets, dashes, dots or spaces.
- Date Regex TesterMatch YYYY-MM-DD dates and rewrite them with named groups.
- IPv4 Address Regex TesterMatch four numbers from 0 to 255 separated by dots.
- Hex Color Regex TesterFind #rgb and #rrggbb colours in a stylesheet or text.
- Password Strength RegexSee which sample passwords pass a rule built from lookaheads.
- Remove Extra Spaces With RegexReplace runs of whitespace with a single space.
- Extract Numbers With RegexPull every number, including decimals and negatives, out of text.
- Regex Replace With Capture GroupsReorder words with $1 and $2 in the replacement.