Every URL has two parts working against each other: the domain, which never changes, and the slug, which is where all the actual information lives. Get the slug wrong — spaces turned into %20, a stray apostrophe, a date baked into an otherwise timeless guide — and you've created a link that's ugly to share and harder for search engines to parse, even if the page itself is great.
What Is a URL Slug?
A URL slug is the part of a URL that comes after the domain name and identifies the specific page. In calquto.com/blog/mortgage-calculator-guide, the slug is mortgage-calculator-guide. Slugs replace page titles — which contain spaces, capital letters, and special characters — with clean, URL-safe text.
💡 The term "slug" itself comes from newspaper newsrooms, decades before the web existed. A slug was the short, working identifier editors and typesetters gave a story before it went to print — a shorthand label used internally, distinct from the eventual published headline. When early web content management systems needed a name for the URL-friendly identifier attached to each article, the newspaper term carried over directly, and it's stuck in web development terminology ever since.
Slug Formatting Rules
A proper URL slug follows a small set of rules: lowercase only — URLs are case-sensitive on most servers, so "Guide" and "guide" can technically resolve to different pages. Hyphens between words, not underscores — Google treats hyphens as word separators but reads underscore-joined text as a single token. No spaces — spaces get encoded as %20 in URLs, which looks broken and is easy to mistype. No special characters — stick to letters, numbers, and hyphens. No stop words (optional) — dropping "a," "an," "the," and "and" keeps slugs tighter without losing meaning.
| Title | Good Slug | Bad Slug |
|---|---|---|
| Mortgage Calculator Guide | mortgage-calculator-guide | Mortgage Calculator Guide |
| How to Save $10,000 | how-to-save-10000 | how_to_save_$10,000 |
| The Best Tax Tips for 2026 | best-tax-tips-2026 | the-best-tax-tips-for-2026 |
SEO Best Practices for URL Slugs
Google and other search engines read slugs as signals of page content. Include the primary keyword — "mortgage-calculator-guide" tells Google what the page is about before it even reads the body. Keep it concise — shorter slugs are more shareable and memorable; aim for 3-5 words. Make it permanent — changing a slug after publishing breaks every inbound link pointing to it, and while 301 redirects help, they aren't a perfect substitute for the original URL's accumulated signal. Avoid dates in slugs unless the date is essential to the content — "tax-tips-2026" goes stale within a year, while "tax-tips" stays evergreen indefinitely. Never keyword-stuff — "mortgage-calculator-mortgage-payment-home-loan" reads as spam to both users and search engines.
💡 The slug appears directly in Google's search results, right below the title. A clean, descriptive slug functions as a second headline of sorts — it tells someone scanning results exactly what they'll find before they even click, which measurably improves click-through rate over a URL full of numbers or gibberish.
Slugs in Popular CMS Platforms
WordPress auto-generates slugs from post titles — always review and edit before publishing, since the defaults often include stop words. Set "Post name" as the permalink structure under Settings → Permalinks. Shopify generates slugs from product titles, editable in the SEO section of each product listing. Webflow auto-generates from the page name, editable in Page Settings. Ghost auto-generates from the post title. Nearly every CMS allows manual slug edits but will warn that changing a slug after publishing requires setting up a redirect to avoid broken links.
Quick Checklist
- Always edit auto-generated slugs before publishing — CMS defaults often include stop words and aren't optimized
- Keep slugs to 3-5 words focusing on the primary keyword
- Use hyphens, not underscores — Google treats hyphens as word separators, underscores join words
- Make slugs permanent — plan before publishing, as changes break inbound links
- Remove dates from slugs unless the content is inherently time-bound
- Set up 301 redirects whenever a slug must change — never let pages return 404
For informational purposes only. Not financial, tax, or legal advice. Consult a qualified professional before making major decisions.