Session ID
An identifier a site gives a visitor for one visit. In URLs it creates a new address per visitor for the same page; Google advises avoiding session IDs in URLs and using cookies instead.
Reviewed by Alexander Yarovenko · Updated: 2026-10-08
A session ID is a unique identifier a website gives to a visitor so it can recognise them from one request to the next, for example to keep a shopping cart. It can live in a cookie or be added to every URL as a parameter such as ?sessionid=6EE2…. The URL form is the SEO problem: each visitor gets different URLs for one page. Google’s advice: wherever possible, avoid session IDs in URLs and consider using cookies instead.
What it is and where the boundary lies
The identifier itself is harmless. Websites need some way to link a visitor’s requests together, and a cookie does that without touching the address. The trouble starts when the ID is placed in the URL and appears in links the crawler can follow: a crawler arrives with a new ID, sees what looks like a new URL for the same content, and finds another link with another ID. Google lists session IDs among the irrelevant parameters that create unnecessarily many URLs pointing to identical or similar content.
How it differs from similar terms
| Term | What it is | Relation to a session ID |
|---|---|---|
| Session ID | an identifier for one visit | the subject here |
| URL parameters | key-value pairs added to a URL | the form a session ID takes in a URL |
| Duplicate content | one content at several URLs | the result of session IDs in URLs |
| Canonical tag | a signal for the preferred URL | a way to consolidate the variants |
| Faceted navigation | filters that create many URLs | another source of URL explosion |
Why it matters
Google says overly complex URLs, particularly with several parameters, can create an unnecessarily high number of URLs pointing to the same or similar content. As a result Googlebot may use much more bandwidth than necessary, or Google Search may be unable to index all the content on the site. A session ID multiplies this directly, since it makes a new URL for every visitor. For people it also causes trouble: a link copied from the address bar carries someone else’s session.
How to find and fix it
- Look at your own URLs. Browse the site and watch the address bar for parameters such as
sessionid,sidorPHPSESSIDthat appear on the way. - Check what Google sees. In the Page indexing report and URL Inspection, look for the same page appearing under several parameter variants, and note which one Google selected as canonical.
- Move the session to a cookie. Configure the application so it keeps the session in a cookie and does not append the ID to links, which is the fix Google recommends.
- Consolidate what remains. Point rel="canonical" on the parameter variants to the clean URL, or redirect them permanently, and link internally to the clean URL only.
- Do not rely on robots.txt for consolidation. Google says not to use it for canonicalization.
Practical example
| URL a crawler may meet | What it is |
|---|---|
| https://example.com/shoes/ | the clean URL |
| https://example.com/shoes/?sessionid=A1B2 | same page, first visitor |
| https://example.com/shoes/?sessionid=C3D4 | same page, second visitor |
With the session in a cookie, all three collapse to the first address.
Common mistakes
- Appending the ID to every link: this is the pattern that creates a URL per visitor.
- Using robots.txt as the fix: Google lists it for blocking problem URLs, but says not to use it for canonicalization; fixing the source is better.
- Forgetting the clean canonical: parameter variants should point to one preferred URL.
- Linking internally to variants: internal links should use the URL you consider canonical.
- Using the same parameter for tracking and sessions: keep tracking separate and trim parameters that do not change content.
How to validate the result
Crawl a sample of your pages and confirm that no links carry a session parameter. Inspect a previously affected URL and check that Google’s selected canonical is the clean address. Watch the Page indexing report for duplicate statuses to shrink, and allow time for recrawling.
More questions
Does a session ID hurt rankings?
Google does not state a ranking effect. It says that session IDs in URLs create many URLs for the same content, which can waste crawling and prevent complete indexing.
What should replace it?
Google says to consider using cookies instead.
Is any parameter in a URL a problem?
No. Google asks you to trim parameters that do not change the content and notes that complex URLs with many parameters are the risk.
Next practical step
Open your site in a clean browser, click through three pages and look at the address bar. If a parameter follows you, ask your developer to move it to a cookie. Then read the URL parameters entry.
Related concepts
- URL parameters — what appears after the question mark.
- Duplicate content — the result.
- Canonical tag — naming the preferred URL.
- Crawl budget — crawling spent on variants.
- URL structure — keeping addresses simple.