How to Use the Regex Library to Find a Predefined Pattern

What the Regex Library is for

Regex Library helps you browse predefined regular-expression patterns for formats such as email addresses, web addresses, IPv4 addresses, ISO dates, and hexadecimal colors. Use it when you need to locate a pattern by category and review the expression with a short description. The tool retrieves patterns from its built-in library; it does not provide a separate field for submitting text to test against a pattern.

How to find a pattern

1. Open the Regex Library.
2. Decide whether you want to browse the library or retrieve one category. To browse, leave the category selector empty. To retrieve one pattern, choose a category such as email, web addresses, IPv4, ISO dates, 24-hour times, UUIDs, or MAC addresses.
3. If you type or select a category, letter case does not matter. For example, EMAIL is looked up in the same way as email.
4. Submit the selection or run the lookup using the available control.
5. Review the returned regular-expression text and its brief description. If you left the selector empty, review the 16 patterns in sorted order. If you supplied a category that is not recognized, change it to one of the available categories and submit the lookup again.

The available categories cover email, web addresses, US phone numbers, IPv4 and IPv6 addresses, ISO dates, 24-hour times, hexadecimal colors, credit card numbers, US ZIP codes, strong passwords, URL slugs, UUIDs, Base64 strings, HTML tags, and MAC addresses. Because the interaction is category-based, copy or adapt a retrieved expression for use in your own workflow rather than looking for a field that accepts candidate text.

How to read the result

A successful category lookup gives you two useful pieces of information: the regular-expression text for the recognized category and a brief description of that pattern. The category is represented in lowercase, even if you used different capitalization when selecting it. With an empty selector, the result is a sorted library of 16 predefined patterns rather than one category-specific entry.

Treat the expressions as starting points for commonly used formats, not as a guarantee that every real-world value will be accepted or rejected correctly. This library does not establish standards compliance or cover formats beyond its listed categories. It also does not test arbitrary candidate text because the exposed interaction only selects and retrieves a predefined pattern. An unrecognized category produces a failed result, so a failure at lookup time indicates that the category selection was not recognized, rather than showing that a candidate value failed a pattern.

Worked example

You need to locate a predefined pattern for an email address before adapting it for a separate development workflow.

Select the email category and submit the lookup. You can also use EMAIL; the category lookup ignores letter case.

The result returns the recognized category as email in lowercase, together with the corresponding regular-expression text for the email format and a brief description of what that pattern matches.

Limitations

• The tool retrieves predefined patterns for its listed categories and does not test arbitrary candidate text or establish coverage beyond those categories.

Common errors

• Selecting a label outside the predefined category list causes a failed lookup. Choose a supported category, such as email, IPv4, or URL slugs, and submit the lookup again.

FAQ

Can I browse the whole regex library?

Yes, if you leave the category selector empty, the tool returns all 16 predefined patterns in sorted order.

Does the category lookup ignore capitalization?

Yes. A supplied category is looked up without regard to letter case, and a recognized category is represented in lowercase in the result.

Can I test my own text with a pattern?

No. The exposed interaction selects a predefined category and retrieves its expression and description; it does not provide a separate candidate value for testing.