If URLs don’t meet Google’s criteria, “Google Search will likely crawl your site inefficiently — including but not limited to extremely high crawl rates, or not at all.” URLs must follow IETF STD 66, with reserved characters percent encoded.
Officially documented · Google Search Central
“Don’t use fragments to change the content of a page, as Google Search generally doesn’t support URL fragments.” If JavaScript changes the content, use the History API. For parameters, use an equal sign between key and value and an ampersand between parameters.
Officially documented · Google Search Central
When possible, use readable words rather than long ID numbers in URLs. “Use words in your audience’s language in the URL (and, if applicable, transliterated words).” Non-ASCII characters in links should be percent encoded.
Officially documented · Google Search Central
“We recommend using hyphens (-) instead of underscores (_) to separate words in your URLs.” Underscores are commonly used to join concepts that belong together, while hyphens clearly mark a word boundary.
Officially documented · Google Search Central
Google clarified the hyphen and underscore guidance on October 23, 2026.
Officially documented · Google Search Central
“Google Search’s URL handling is case sensitive”, so /APPLE and /apple are distinct URLs. If your server treats them the same, use one case throughout.
Officially documented · Google Search Central
“Overly complex URLs, especially those containing multiple parameters, can cause problems for crawlers by creating unnecessarily high numbers of URLs that point to identical or similar content on your site.” Additive filtering is a common cause. In Google’s hotel example, Googlebot only needs a small number of lists from which it can reach each hotel’s page.
Officially documented · Google Search Central
See Crawl budget for when crawl volume matters, and Canonical URL signals for consolidating the duplicates that parameters create.