URL Slug Best Practices: What Google Recommends
Google has been unusually specific about URL best practices compared to many other SEO factors. The guidelines are documented, the technical reasoning is explained, and the recommendations have been consistent for over a decade. This guide compiles everything Google officially recommends about URL slugs — from hyphens versus underscores to keyword placement and URL length — with practical examples showing how to apply each rule to your own content.
Google's Official URL Guidelines
Google's URL guidance is split between several sources: the Search Central documentation, public statements from Google engineers, and implicit recommendations observable from how Google's crawler and indexing systems behave. The core official guidance includes: use hyphens to separate words in URLs, keep URLs as simple and descriptive as possible, avoid using session IDs and excessive parameters in crawlable URLs, use lowercase letters, and ensure each page has a canonical URL. Google's documentation explicitly states: Use hyphens (-) instead of underscores (_) in your URLs. This is one of the oldest and most consistently cited URL recommendations and is grounded in technical behavior: Google's tokenizer treats hyphens as word separators but treats underscores as word joiners. A URL like seo-tools-for-beginners tells Google it contains four words; seo_tools_for_beginners is treated as one long word, which harms keyword recognition. On URL length, Google's John Mueller has stated that shorter URLs are generally better for usability and sharing, but that URL length itself is not a significant ranking factor. However, unnecessarily long URLs often indicate poor content organization — stuffing keywords into slugs is the URL equivalent of keyword stuffing, and Google's systems are trained to recognize and discount it. On keyword inclusion, Google's guidelines acknowledge that having keywords in URLs can be a minor relevance signal but caution against keyword stuffing in URLs. The right approach is one clear, descriptive keyword phrase per URL slug — not a list of every possible keyword variation. On folder depth, Google recommends making URLs as short as possible while maintaining logical hierarchy. A URL like example.com/blog/seo/url-slugs is preferable to example.com/category/subcategory/sub-subcategory/post-type/url-slugs.
Hyphens, Underscores, and Spaces: The Definitive Answer
The hyphens-versus-underscores question is one of the most frequently asked URL questions in SEO, and Google has answered it definitively and repeatedly. Yet many sites still use underscores, either through CMS defaults or developer preference. Here is everything you need to know. Hyphens are treated as word separators by Google's text processing systems. When Google tokenizes a URL like blue-running-shoes, it reads three separate words: blue, running, shoes. This means the URL contributes to keyword matching for all three words and their combinations. Underscores are not treated as word separators. A URL like blue_running_shoes is tokenized as a single string: blue_running_shoes. This string does not match the individual words blue, running, or shoes in Google's index. The practical implication is that hyphenated slugs provide keyword relevance that underscore slugs do not. Spaces in URLs are encoded as %20, which creates ugly, unreadable URLs: blue%20running%20shoes. Some systems automatically convert spaces to plus signs (+) in certain URL contexts. Neither is acceptable for a clean, readable URL slug. Always convert spaces to hyphens. Plus signs (+) have a specific meaning in query strings (they represent spaces in URL-encoded form parameters), so using them in URL path segments creates potential parsing ambiguity. Avoid them in slugs. Periods (.) are allowed in URL paths but are associated with file extensions (.html, .php, .pdf). Using periods as word separators — blue.running.shoes — is unusual and creates ambiguity that some parsers handle incorrectly. Stick to hyphens. The practical takeaway: if you are building a new site or CMS configuration, set the default permalink format to use hyphens. If you are auditing an existing site that uses underscores, changing the URLs to hyphens is a meaningful SEO improvement but requires 301 redirects from every old URL to the corresponding new URL.
Keyword Placement and Slug Length
Google uses words in URLs as a relevance signal — but the signal is modest, and there are diminishing returns that make over-optimizing slug length counterproductive. The keyword should appear in the slug, ideally at or near the beginning. A slug that starts with the target keyword — create-seo-friendly-slugs — gives Google the strongest keyword signal. A slug that buries the keyword after filler words — the-most-comprehensive-guide-to-creating-seo-friendly-slugs — dilutes it. Lead with the keyword. Do not repeat keywords in the slug. Slug repetition — seo-seo-tools-best-seo-tool-for-seo — is treated as spam. Use the keyword once, clearly. For multi-word keywords, keep the phrase intact. If your target keyword is url slug best practices, keep the words together and in order in the slug: url-slug-best-practices. Do not reorder them or add words between them. The optimal slug length is three to six words or roughly 20 to 60 characters. Within this range, slugs are descriptive, readable, and contain the keyword without unnecessary padding. Slugs shorter than three words may be too vague (tools, guide, post); slugs longer than eight words add noise that diminishes the keyword signal of each individual word. Avoid adding folder names that duplicate the slug keyword. If your URL structure is /blog/seo/url-slug-seo-guide, the word seo appears twice — once in the folder and once in the slug. This is redundant. Use /blog/seo/url-slug-guide instead, trusting that the /seo/ folder provides enough topical context. Date-based slugs (2026/05/how-to-create-slugs) are used by some news organizations and time-stamped blogs. The date adds no keyword value and adds unnecessary characters. Unless your CMS requires dates in URLs, keep them out of the slug.
Canonicalization and URL Consistency
URL consistency is a separate but closely related issue to slug quality. Even a perfectly formed slug can cause SEO problems if the same content is accessible at multiple URLs — a common issue that dilutes link equity and creates indexing confusion. The most common consistency issue is www versus non-www. If your site is accessible at both https://example.com/post and https://www.example.com/post, you have a canonicalization issue. Google recommends choosing one version and using a 301 redirect from the other, plus a canonical tag confirming the preferred URL. A slug generator cannot fix this for you, but being aware of it ensures you are building clean URLs on top of a clean domain setup. Trailing slashes are another common inconsistency. https://example.com/post/ and https://example.com/post are technically different URLs. Most servers handle this with automatic redirects, but confirm your CMS consistently uses one form or the other. Use a canonical tag to specify the preferred version. Case sensitivity is a slug issue that is often overlooked. Linux-based web servers treat /Post and /post as different URLs. Apache and Nginx typically serve them separately unless configured otherwise. Always use all-lowercase slugs and ensure your server either redirects uppercase variants to the lowercase canonical or your CMS does not generate uppercase URLs. Query parameters in URLs — https://example.com/post?ref=social&utm_source=twitter — do not affect the canonical slug, but they can create duplicate content if Google indexes parameterized versions of your pages. Use the canonical tag to point all parameter variations to the clean, slug-only URL. Google Search Console's URL Parameters tool helps you tell Google which parameters to ignore during crawling. When using a slug generator, always copy the output and verify it matches the URL your CMS actually saves. Some platforms apply their own slug transformations on top of whatever you paste, potentially introducing unexpected characters or truncations.
Frequently Asked Questions
- Does Google penalize sites for having messy URLs?
- Google does not apply a direct penalty for non-ideal URLs — there is no manual action for using underscores instead of hyphens, for example. However, messy URLs cause indirect ranking harm through reduced keyword relevance signals, lower click-through rates from poor readability in search results, and duplicate content issues when URL inconsistencies cause the same page to be indexed under multiple addresses. The cumulative effect of consistently poor URL structure across a large site is a meaningful SEO disadvantage compared to sites with clean, consistent URL patterns.
- Should I include stop words like 'how', 'to', 'the', 'for' in my slugs?
- The general best practice is to remove common stopwords to keep slugs short. However, there is an important exception: when the stopword is part of the target keyword phrase. How-to tutorials often rank well for how-to queries specifically — the words how and to are part of the query intent. If you are targeting the keyword how to create url slugs, the slug how-to-create-url-slugs is appropriate and removing the how-to would change the keyword match. Use a slug generator with stopword removal as a starting point, then manually restore any stopwords that are part of your actual target keyword.
- What happens to SEO if I change a URL slug after publishing?
- Changing a URL slug after publishing causes the old URL to return a 404 error unless you set up a 301 redirect from the old URL to the new one. A 301 redirect preserves most of the original URL's link equity and tells Google the page has permanently moved. Without a redirect, you lose all backlinks pointing to the old URL, any Google Search Console data associated with it, and any social shares or bookmarks. Always implement a 301 redirect when changing a published URL slug. The SEO impact is usually minimal if the redirect is set up correctly, but a missed redirect can result in significant traffic loss.