About Hex Color Regex Tester
This page opens with a pattern for hex colour codes: a hash sign followed by three or six hexadecimal digits, then a word boundary so longer runs do not match. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
It finds 3 colours in the sample: #fff, #0084FF, #1a2b3c. The values "#12", "#ggg" and "#12345" are left out because they have the wrong length or invalid digits.
Eight-digit hex codes with an alpha channel need the group repeated to {4} or a separate alternative.
How to use Hex Color Regex 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
#(?:[0-9a-fA-F]{3}){1,2}\b gives #fff | #0084FF | #1a2b3c
(?:[0-9a-fA-F]{3}){1,2} means three digits, once or twice.
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.
How do I also match 8 digit hex colours?
Use #(?:[0-9a-fA-F]{3,4}){1,2}\b to allow 3, 4, 6 or 8 digits, where the extra digits are the alpha channel.
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.
- 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.
- Regex Named Groups TesterCapture the level, service and message of a log line by name.