What Is URL Parameter?

How URL Parameters Work

A URL parameter is how a web page receives instructions through its address. Everything after the ? is the query string, and inside it each parameter is a key=value pair — ?color=grey tells the page to show grey items. Add more and you chain them with &: ?color=grey&size=small&sort=price. The server reads these keys and decides what to render.

Parameters do wildly different jobs, and the SEO consequences depend on which job. Some are content-defining: ?color=grey genuinely changes which products appear, so the resulting URL is arguably a distinct page worth indexing. Others are presentational: ?sort=price reorders the same items without changing what they are. And some are passive: a tracking tag like ?utm_source=email or a session ID changes nothing a user sees. The trouble is that to a naïve crawler, all three look like brand-new URLs pointing at content it must fetch and evaluate.

That is why parameters sit at the center of faceted navigation problems. Google’s faceted navigation guidance uses the example https://example.com/items.shtm?products=fish&color=radioactive_green&size=tiny and notes that changing any of the parameters “would show a different set of items.” Multiply the options across several filters and the URL space explodes. Google’s own warning is that these URLs “seem to be novel and crawlers can’t determine whether the URLs are going to be useful without crawling first,” so crawling them “tends to cost sites large amounts of computing resources due to the sheer amount of URLs.” Every request spent on a pointless combination is a request not spent on a real new page — a direct hit to crawl budget.

Managing Parameters

Because parameters can spawn duplicates, the job is to tell search engines which variants matter. The main tools are a canonical URL tag pointing near-duplicate variants back to the clean version, a robots.txt disallow to keep crawlers out of worthless combinations entirely, and — for pure UI state — URL fragments after a #, which Google generally does not crawl. What no longer exists is a dedicated Google setting for this, which is the crux of the worked example below.

Example of URL Parameters

The most instructive real event is Google’s own retirement of the tool built for this exact problem. In a March 2022 Search Central post titled “Spring cleaning: the URL Parameters tool”, Google announced it was deprecating the URL Parameters tool in Search Console, and it went offline on 28 April 2022.

The reasoning is specific and quantified. The tool had launched in 2009, back in the Webmaster Tools era, when parameters like session IDs were rampant and site owners wanted granular control over how Google treated each one. Thirteen years later, Google said its crawlers had simply gotten better at guessing which parameters matter — so much so that, by its own estimate, only about 1% of the parameter configurations site owners had specified in the tool were still useful for crawling. Google added that no action was required from existing users: its crawlers would continue determining how to handle parameters automatically, and owners wanting more control should use robots.txt rules or canonical tags instead.

The lesson lands in two parts. First, parameters are enough of a real crawling problem that Google maintained a dedicated tool for them for over a decade. Second, the answer is no longer a tidy dashboard toggle — Google now expects its crawlers to figure most of it out, and expects you to handle the rest with standard directives. That shifts the responsibility onto site owners to design parameter handling into the site itself, deciding upfront which parameters deserve an indexable URL and canonicalizing or blocking the ones that only ever produce duplicates.

Frequently Asked Questions

The Bottom Line

A URL parameter is the key=value data tacked onto a URL after a question mark to drive filtering, sorting, sessions, or tracking. Handled with care it is ordinary web plumbing; handled carelessly it multiplies your URLs into a duplicate-content and crawl-budget problem. With Google’s dedicated parameter tool gone since 2022, deciding which parameters deserve their own URL and neutralizing the rest is now squarely the site owner’s job.