What is a slug in a URL?

A slug is the human-readable, URL-safe part of a web address that identifies a page. For example, in https://example.com/blog/what-is-a-slug, the slug is 'what-is-a-slug'. Slugs are typically derived from the page title by lowercasing, replacing spaces with hyphens, and removing special characters.

How is a slug generated from a title?

The standard transformation: 1) Lowercase everything. 2) Replace spaces with hyphens. 3) Remove or transliterate non-ASCII characters. 4) Remove characters that are not letters, numbers, or hyphens. 5) Collapse multiple hyphens. 6) Trim leading and trailing hyphens.

Should slugs use hyphens or underscores?

Hyphens are strongly preferred. Google treats hyphens as word separators and underscores as part of a word. 'what-is-a-slug' is indexed as four words; 'what_is_a_slug' is indexed as one token. Use hyphens for SEO.

What is a Slug?

A slug is the URL-friendly identifier derived from a page title. The title "What is a Slug?" becomes the slug what-is-a-slug — lowercase, spaces replaced with hyphens, special characters removed.

How a Slug Is Generated

Given the title "Hello, World! (2024)", a slug generator applies these steps:

Lowercase: hello, world! (2024)
Replace spaces with hyphens: hello,-world!-(2024)
Remove non-alphanumeric characters (keep hyphens): hello-world-2024
Collapse consecutive hyphens: hello-world-2024
Trim leading/trailing hyphens: hello-world-2024

For non-ASCII characters (accented letters, CJK, Arabic), the best practice is to transliterate to ASCII first — e.g. é → e, ü → u.

Hyphens vs Underscores

Google's John Mueller has confirmed hyphens are preferred over underscores in slugs. A hyphen acts as a word separator in search indexing; an underscore does not. best-coffee-shops is indexed as three separate words; best_coffee_shops is a single token.

Where Slugs Are Used

Blog and CMS URLs: /blog/what-is-a-slug
Product pages: /products/blue-denim-jacket
Category and tag pages
API endpoints: /api/users/john-doe
Git branch names (by convention)

Generate a URL slug from any text: Open Slug Generator →

Frequently Asked Questions

Should slugs include stop words?

It depends. Short slugs are cleaner (/blog/slug-guide) but longer descriptive slugs match more search queries (/blog/what-is-a-url-slug). For SEO, include the target keyword; remove truly meaningless filler words like "a", "the", "is" only if the slug is excessively long.

Can I change a slug after publishing?

You can, but it breaks existing links and resets any SEO equity unless you set up a 301 redirect from the old slug to the new one. Change slugs sparingly on established pages.

Related Terms

URL Encoding — How special characters are safely encoded in URLs.
HTTP Redirects — How to handle slug changes without breaking links.