Regex for URL Slug Validation — Lowercase, Hyphenated

Regex for URL Slug Validation

A URL slug is the human-readable portion of a URL path, typically derived from a title. SEO and routing best practices recommend lowercase ASCII letters, digits, and single hyphens between words.

Standard Pattern

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

This pattern enforces:

• One or more lowercase letters or digits to start
• Zero or more groups of - followed by alphanumerics
• No leading, trailing, or consecutive hyphens

Tested Examples

Input	Valid?
hello-world	yes
my-blog-post-2024	yes
a	yes
Hello-World	no (uppercase)
-hello	no (leading hyphen)
hello--world	no (double hyphen)
hello_world	no (underscore)
hello world	no (space)

With Length Limits

Most CMSs cap slugs at around 60–80 characters for SEO and URL display:

^[a-z0-9]+(?:-[a-z0-9]+){0,15}$

Or use a length anchor:

^(?=.{3,80}$)[a-z0-9]+(?:-[a-z0-9]+)*$

Generating Slugs from Titles

Validation is one half; generation is the other. A typical pipeline:

title
  .toLowerCase()
  .normalize("NFD").replace(/[\u0300-\u036f]/g, "")  // strip accents
  .replace(/[^a-z0-9]+/g, "-")
  .replace(/^-+|-+$/g, "")

Unicode Slugs

Some platforms allow Unicode (e.g. Wikipedia). To accept letters in any script:

^[\p{L}\p{N}]+(?:-[\p{L}\p{N}]+)*$

(Requires the u flag.)

Why It Matters

Strict slug validation prevents broken canonical URLs, duplicate routes from case-only differences, and accidental whitespace that breaks redirect rules.