Google updated its Search Central documentation on October 23 to clarify its long-standing guidance on URL word separators: use hyphens, not underscores. According to the official changelog entry, titled “Updated guidance on crawlable URL structures,” the revision explains that hyphens mark word boundaries while underscores have historically kept concepts together — a programming convention borrowed from names like format_date. Google says the change synchronizes the documentation with episodes of its “The Non-Canonical Cabinet” video series. It introduces no new ranking rule and requires nobody to rename existing pages.
What the Updated Guidance Says
The revised URL structure best practices spell out the distinction for site owners. Hyphens provide a clear boundary between words, helping both people and search engines identify the concepts in an address. Underscores, by contrast, come from a programming tradition where a name like format_date is treated as a single concept — which is why Google does not recommend them as word separators.
Google’s examples favor /summer-clothing/ over /summer_clothing/. The same recommendation extends into query strings: color-profile=dark-grey beats the underscore-separated equivalent. Beyond the separator question, the guide repeats its standing advice — use readable words, write in your audience’s language, and keep unnecessary parameters out of URLs — giving teams a consistent format when planning a new section or catalog.
No Ranking Change and No Rename Requirement
Search Engine Watch, which reported the changelog entry, emphasized that the update explains an existing preference rather than introducing a new rule. Nothing about how Google ranks pages changed on October 23, and the changelog announces no requirement to rename pages that already use underscores.
That matters because URL changes are expensive. Google’s own site-move guidance, which the updated page points to, treats a path change as a migration: map each old address to its replacement, configure permanent redirects (preferably server-side HTTP 301 or 308 responses), update internal links, refresh the new pages’ self-referencing canonical tags and the sitemap, and test that every redirect reaches the corresponding page. The guidance warns that significant URL changes can produce temporary ranking fluctuations while pages are recrawled and reindexed — for a medium-sized site, new URLs can take a few weeks or more to replace old ones in results, and larger sites may take longer.
Check Your Defaults Instead of Renaming
The practical takeaway from the update is aimed at publishing systems rather than archives. If a CMS generates slugs automatically, inspect the address it creates for a new article or product page. Setting the default separator to hyphens there applies the recommendation to everything new — without moving any page that readers and other websites already link to.
Notably, Google’s Change of Address tool is not part of this workflow: it exists for moves between domains or subdomains, a different operation from changing an article’s slug on the same domain. And for sites that do decide to migrate underscore URLs to hyphens, the changelog points to the same migration discipline Google has documented for years — redirects, canonicals and sitemaps, not a find-and-replace.
Why It Matters
The hyphens-versus-underscores question is one of search’s oldest folk debates, and Google settling it in writing — with the programming-history rationale — gives SEOs a citable source to end it. The deeper signal is procedural: Google’s documentation now ships in sync with its video series, and the changelog has become the site’s running record of what the company actually recommends. That record is also where Google quietly maintains its positions on newer topics, from image format support in Images and Discover to how commerce features behave in Search. For publishers, the October 23 entry is a reminder to treat the changelog as a beat to follow, not an archive to browse.
Background
Google’s preference for hyphens dates back to the earliest webmaster guidelines, when underscores in URLs were a common cause of crawling confusion. The company has restated it many times — including in developer-facing updates over the years — but the October 23 revision is the first to frame the reasoning explicitly in programming terms and to tie the documentation to the “Non-Canonical Cabinet” video series, suggesting Google wants the same explanation repeated consistently across its video and written channels.
Source: Google Search Central, Search Engine Watch
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