Regex pattern library

12 curated, production-ready regular expressions. Each comes with a plain-English explanation, matching and non-matching examples, edge cases that bite people, and ready-to-paste code in 13 languages.

Validation

4 patterns

Patterns that answer 'is this input shaped correctly' for things like email addresses, URLs, and IPs.

Email address

email regex

Practical, permissive email validator that catches typos without rejecting real addresses.

/^[^\s@]+@[^\s@]+\.[^\s@]+$/i

Open

URL (HTTP/HTTPS)

url regex

Practical HTTP/HTTPS URL validator that accepts real URLs and rejects the obvious junk.

/^https?:\/\/[^\s/$.?#].[^\s]*$/i

Open

IPv4 address

ipv4 regex

Strict IPv4 that rejects out-of-range octets like 999.999.999.999.

/^(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)$/

Open

US phone number

us phone number regex

US phone number that accepts every common formatting people actually type.

/^(?:\+?1[\s-.]?)?(?:$\d{3}$|\d{3})[\s-.]?\d{3}[\s-.]?\d{4}$/

Open

Format

5 patterns

Patterns that match well-defined data formats — dates, versions, identifiers.

UUID v4

uuid regex

RFC 4122 UUID version 4 — the random-bytes variant nearly every database uses.

/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i

Open

ISO 8601 date / datetime

iso 8601 date regex

ISO 8601 dates and optional datetimes with timezone, the format every modern JSON API speaks.

/^\d{4}-\d{2}-\d{2}(T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2})?)?$/

Open

Semantic version

semver regex

The official semver.org reference regex — major.minor.patch with optional pre-release and build metadata.

/^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$/

Open

Hex color

hex color regex

CSS hex color in 3-, 6-, or 8-character (with alpha) form.

/^#(?:[0-9a-f]{3}|[0-9a-f]{6}|[0-9a-f]{8})$/i

Open

URL slug (kebab-case)

slug regex

Lowercase alphanumerics with single hyphens between words — the canonical URL slug shape.

/^[a-z0-9]+(?:-[a-z0-9]+)*$/

Open

Extraction

1 pattern

Patterns for pulling structured tokens out of running text — JWTs, IDs, references.

JWT (JSON Web Token)

jwt regex

Three base64url-encoded segments separated by dots — the JWT shape.

/^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+$/

Open

Security

2 patterns

Patterns for security-adjacent checks — credit cards, password strength.

Credit card (shape-only)

credit card regex

Shape check for credit-card numbers — 13 to 19 digits with optional spaces/hyphens.

/^(?:\d[ -]*?){13,19}$/

Open

Strong password

password regex

12+ characters with upper, lower, digit, and symbol — the familiar 'complex password' rule.

/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W_])[A-Za-z\d\W_]{12,}$/

Open

Not finding what you need?

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