SEO-friendly URLs: how to build slugs that rank

CCompare these two search results for "compress PDF":

• —blipfiles.com/post.php?id=42857&cat=4
• —blipfiles.com/compress-pdf

Both can have the same content. But the second gets ~25% more clicks at the same SERP position. It's not magic — humans and bots both read the URL as a relevance signal. A slug with the keyword reinforces that the page IS about the topic.

A slug is the final part of a URL — after the domain and before any query strings. In "blipfiles.com/compress-pdf?utm_source=email", the slug is "compress-pdf". Best practice: make it readable, descriptive, and built from the page's keywords.

• —All lowercase. URLs are case-sensitive on some servers — /Compress and /compress can become different pages.
• —Hyphens, not underscores. Google treats "compress-pdf" as two words, "compress_pdf" as one. Always hyphens.
• —No accents or special chars. "compress-pdf-français" works, but becomes "compress-pdf-fran%C3%A7ais" when copied. Ugly and breaks in some email clients.
• —Short: 3-5 words. Long slugs dilute the weight of each individual word.
• —Include the main keyword. If the page is about "PDF compression", the slug should contain "compress-pdf".
• —No unnecessary stop-words. "how-to-compress-a-pdf-file" → "compress-pdf" is stronger. Stop-words ("a", "the", "for") dilute the signal.
• —Unique and stable. Never change a production slug without a 301 redirect — you'll lose all backlinks.

Repeating the category in the slug

blipfiles.com/pdf/compress-pdf-online — "pdf" appears 2x. Worse for SEO because it dilutes relevance. Use /compress-pdf alone OR /pdf/compress, but never both together.

Keyword stuffing

/compress-pdf-online-free-no-watermark-2026 — Google has penalized this since 2012. Clear bad-SEO signal. Focus on 1 main keyword per slug.

Changing slugs without redirects

You change /articles/x to /blog/x and forget the 301 redirect. Result: every backlink becomes a 404, you lose authority, and visitors clicking old links see errors. Whenever you change a slug, set up the 301.

Multi-language sites

Localize the slug, not just the content. /pt/comprimir-pdf, /en/compress-pdf, /es/comprimir-pdf. An English slug on a Portuguese version of the site confuses both Google and users.

Dates in URLs (blogs)

Avoid. /2024/04/15/post-title visually ages — by 2026 it looks outdated even if the content was refreshed. /post-title without the date is more flexible for updates.

Special characters (?, &, =)

Query strings are fine for temporary parameters (UTM, filters), never for the main slug. /product.php?id=42 ages badly. /product/product-name ranks better.