How to read one
Everything before the question mark is the page. After it, each parameter is a key, an equals sign and a value, and an ampersand joins the next one: ?color=blue&sort=price. Google's URL structure guidance recommends exactly this format.
Two kinds
Parameters do one of two jobs:
- Content parameters change what the page shows: a filter (?color=blue), a sort order (?sort=price), a page of results (?page=2) or a site search (?q=boots).
- Tracking parameters leave the page as it is and record where the visit came from, such as utm_source and utm_campaign for analytics, or an ad click ID like gclid.
When they cause SEO problems
Each new combination is a new URL. Google's URL structure guide warns that URLs with many parameters can create large numbers of addresses for identical or similar content, so Googlebot may use far more bandwidth than it needs, or Google may be unable to index all the content on your site. Filters that combine, such as color plus size plus price, are the usual cause on shop sites.
How to keep them tidy
Google's URL structure and faceted navigation guides point to three habits:
- Use as few parameters as you can, and drop the ones that don't change the content.
- Give parameter versions a canonical tag that names the clean page. Google's own example is a product page reached through ?gclid=ABCD.
- For filter pages you don't need in Google, its faceted navigation guide suggests blocking them in robots.txt.