What Is a URL Slug?

A URL slug is the final component of a web URL — the human-readable part that identifies the specific page. In the URL https://example.com/blog/what-is-seo/, the slug is what-is-seo. Slugs are:

• Lowercase letters and numbers only
• Words separated by hyphens
• No spaces, underscores, or special characters
• Descriptive of the page content

The word "slug" comes from the newspaper publishing world, where it referred to a short name given to an article while it was being edited.

Why URL Slugs Matter for SEO

Google uses the URL as a ranking signal. A slug containing your target keyword helps search engines understand what the page is about. It also appears in search results beneath the title, so a clear, descriptive slug can improve click-through rates.

Slug Type	Example	SEO Value
Descriptive	/how-to-compress-images	High — tells Google and users what the page is
Numeric ID	/page?id=4821	None — no keyword signal
Date-based	/2024/01/15/post	Low — dates can make content look outdated
Keyword-rich	/image-compression-guide	High — clear and concise

Rules for Creating a Good Slug

1. Use lowercase only — /My-Blog-Post and /my-blog-post can be treated as different URLs.
2. Use hyphens, not underscores — Google treats hyphens as word separators.
3. Include your primary keyword — keep it natural and descriptive.
4. Remove stop words — drop 'a', 'the', 'and', 'or', 'in' where possible.
5. Keep it short — 3–5 words is the sweet spot. Under 75 characters is recommended.
6. Avoid dates — dates in slugs can make evergreen content look outdated.
7. No special characters — apostrophes, commas, and ampersands break URLs.

Hyphens vs Underscores in Slugs

This is one of the most common URL mistakes. Google's guidance is clear: use hyphens. Google treats a hyphen as a word separator, so email-marketing-guide is indexed as three separate words. An underscore is not a separator, so email_marketing_guide is indexed as a single compound word, losing keyword targeting for each individual term.

John Mueller from Google confirmed this in a 2016 Webmaster Hangout: "We do treat hyphens as word separators, but underscores are not word separators."

Changing an Existing Slug

If you need to change a slug on an existing page, always set up a 301 redirect from the old URL to the new URL. Without a redirect, anyone who has bookmarked the old URL or linked to it will hit a 404. A 301 redirect preserves the SEO "link juice" accumulated by the original URL and transfers it to the new one.

How to Generate a URL Slug Automatically

Use the ToolsBox Text to Slug generator. Paste any title or phrase and the tool instantly converts it to a clean slug — lowercased, with spaces replaced by hyphens and special characters stripped. It handles accented characters too, converting é to e and ñ to n for URL-safe output.

Frequently Asked Questions

What is a URL slug?

A URL slug is the human-readable end part of a web URL. In https://example.com/blog/what-is-seo/, the slug is 'what-is-seo'. Slugs use lowercase letters, numbers and hyphens — no spaces or special characters.

Why do slugs use hyphens instead of underscores?

Google treats hyphens as word separators and underscores as joiners. 'keyword-research' is indexed as two words ('keyword' + 'research'), while 'keyword_research' is indexed as one compound word. Hyphens give better SEO targeting for each individual keyword.

Should I include stop words in a URL slug?

Generally no. Drop words like 'a', 'the', 'and', 'of' to keep slugs concise. 'how-compress-images' is better than 'how-to-compress-your-images'. However, readability matters too — don't make slugs incomprehensible in pursuit of brevity.

Can I change a slug after publishing?

Yes, but always set up a 301 redirect from the old URL to the new one. Without a redirect you get 404 errors for anyone who had the old link, and you lose the SEO equity (backlinks, rankings) built up by the original URL.