Regex Builder

1. Select a value type. Begin with the preset closest to the business field.
2. Set match scope. Keep whole-value matching on for form-field checks; turn it off for search inside text.
3. Use Custom when needed. Enter only the base pattern, without slash delimiters.
4. Generate the expression. Copy the pattern and any displayed flag hint.
5. Prove the rule. Test positive, negative, boundary, and hostile inputs in the target regex engine.

Generate a search pattern or whole-value rule

A pattern generator must know whether the expression should locate a fragment or describe an entire value. With complete-value matching disabled, an email-like pattern can find an address inside a support note. With it enabled, any extra prefix, suffix, or trailing text makes the whole input fail.

The builder adds ^(?: before the base and )$ after it. The non-capturing group preserves precedence without creating an extra numbered capture. This is useful for form-field checks, import rules, and configuration values.

Regex pattern generator examples

Email-like value

Type: Email address
Complete value: yes
Pattern: ^(?:[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,})$
Flags: i

IPv4 address with bounded octets

Type: IPv4 address
Complete value: yes
Pattern: ^(?:(?:(?:25[0-5]|2[0-4]\d|1?\d?\d)\.){3}(?:25[0-5]|2[0-4]\d|1?\d?\d))$

ISO-shaped date

Type: ISO date
Pattern: ^(?:\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01]))$

Lowercase URL slug

Type: URL slug
Pattern: ^(?:[a-z0-9]+(?:-[a-z0-9]+)*)$
Accepts: regex-tools-2026
Rejects: Regex Tools

Custom order code

Type: Custom
Base: [A-Z]{3}-\d{4}
Complete value: yes
Pattern: ^(?:[A-Z]{3}-\d{4})$

What each preset does and does not validate

Email and URL presets cover familiar application input but do not reproduce every relevant standard. The ISO date preset constrains month and day ranges but does not know leap years or month length. The UUID preset accepts standard variants and versions in a canonical hyphenated shape. The IPv4 preset constrains octets to 0–255.

Slug, integer, decimal, and hex-color patterns intentionally define narrow shapes. If a project allows Unicode slugs, locale-specific decimal separators, leading zeros, or shorthand color rules, change the business specification before changing the regex.

Wrap a custom base expression safely

Custom mode accepts the expression itself, not slash delimiters or trailing flags. For example, enter [A-Z]{3}-\d{4} rather than /[A-Z]{3}-\d{4}/g. Choose complete-value matching if the complete field must be one order code.

The builder does not rewrite or explain an arbitrary custom expression. Keep it readable, use non-capturing groups for precedence, and document the business meaning beside application code.

Test generated regex before production

Create a small matrix containing normal accepted values, minimum and maximum lengths, missing sections, duplicated separators, unexpected spaces, mixed case, Unicode, and near-matches that must fail. Test long nonmatching input when a custom pattern contains repetition or alternatives.

PCRE, JavaScript, Python, Java, and .NET differ in features and escaping. A pattern copied into JSON or a programming-language string may require another layer of backslashes. Use the PCRE2 pattern reference for this output, then verify it in the final runtime.

Related Trexmi tools

Test the generated expression with Regex Tester PRO, use it to transform text in Regex Replace, or collect its matches with Regex Extractor.