Glossary Term

Parameter Passthrough

glossary parameter passthrough featured

Parameter passthrough is the forwarding of URL parameters from an incoming link to the next URL in a redirect or page hand-off. When a visitor clicks a short link or redirect carrying ?utm_source=newsletter, passthrough makes sure that same parameter arrives on the final landing page. Without it, campaign tags and click IDs are silently stripped and the visit is misattributed.

How Parameter Passthrough Works

A redirect receives a request, reads the query string, and appends it to the destination before sending the visitor on. Every hop has to do this, or the parameters stop at that hop.

Click:   https://go.example.com/spring?utm_source=newsletter&utm_medium=email
Redirect: 302 → https://example.com/sale?utm_source=newsletter&utm_medium=email

The same redirect without passthrough sends the visitor to https://example.com/sale with nothing attached. GA4 then records the session as direct traffic or as the referring domain, not the email campaign.

Passthrough applies to any URL parameters: UTM tags, ad click IDs like gclid and fbclid, affiliate IDs, and custom keys such as promo=spring25. Some link shorteners call the feature “parameter passing”. Bitly, for example, offers it on some paid plans so parameters added after a short link reach the destination.

Why Parameter Passthrough Matters

Analytics tools read parameters on the landing page, not on the link that was clicked. If a link redirect drops the query string, the data is gone before any tracking script runs.

Google’s own Analytics help documentation lists redirects as a cause of lost GCLID values. Its recommended test is to add ?gclid=123-abCD to the destination URL and check whether it survives in the address bar. A lost GCLID breaks the Google Ads to GA4 link, so paid clicks show up without campaign data.

Passthrough also matters beyond redirects:

  • Landing page to form: UTM values copied into hidden form fields so the CRM records the lead source.
  • Domain to domain: GA4’s _gl linker parameter carries session data during cross-domain tracking.
  • Partner hand-offs: affiliate and click IDs forwarded to a checkout or app store page for conversion matching.

Where Parameters Get Dropped

Most passthrough failures happen at infrastructure the marketing team does not control.

  • HTTP to HTTPS and www rewrites written without the query string.
  • Mobile redirects, such as www to m. subdomains. Google names these as a common GCLID failure.
  • Apache RewriteRule with a new query string. If the target URL contains its own ?, Apache discards the original query string unless the rule includes the QSA (query string append) flag.
  • Nginx rewrites ending in ?, which explicitly drop the original arguments.
  • JavaScript redirects that set window.location to a hardcoded URL.
  • Login, consent, or geo walls that send visitors to an interstitial page and back without the original parameters.

How to Configure Parameter Forwarding

Forward the full query string at every hop. Common server examples:

# Apache: keep the original query string alongside a new one
RewriteRule ^spring$ https://example.com/sale?ref=go [R=302,L,QSA]

# Nginx: $request_uri includes the path and the query string
return 301 https://example.com$request_uri;

// JavaScript: append the current query string before redirecting
window.location.replace("https://example.com/sale" + window.location.search);

When the destination already has parameters, merge with & instead of adding a second ?. A URL like /sale?ref=go?utm_source=email corrupts both values.

To confirm the fix, run the tagged link through linkutm’s redirect checker and check that the parameters appear on the final URL, not just the first hop.

Frequently Asked Questions

What is URL parameter passthrough?

URL parameter passthrough is the practice of carrying query parameters from a clicked link to the final destination URL. It is used by link shorteners, redirect services, and landing pages. Its main job is to keep UTM tags and click IDs intact so analytics tools can attribute the visit.

Is parameter passthrough the same as parameter forwarding?

Yes. Parameter passthrough, parameter forwarding, URL parameter forwarding, and parameter passing all describe the same behavior. Vendors pick different names, but each means that query parameters on the incoming request are appended to the outgoing URL.

Do 301 redirects keep query parameters?

A 301 redirect keeps query parameters only if the server rule forwards them. The status code itself does not decide this. Nginx’s $request_uri and Apache’s Redirect directive preserve the query string, while a rewrite that sets a new query string drops it unless configured otherwise.

Why are my UTM parameters missing on the landing page?

The most common cause is a redirect between the click and the landing page that strips the query string. Other causes include a JavaScript redirect, a consent or login interstitial, or a URL with two ? characters. Test each hop with a placeholder parameter to find where it disappears.

Does parameter passthrough create duplicate parameters?

It can. If both the short link destination and the clicked link include utm_source, the final URL may carry two utm_source keys. Which value wins depends on the tool reading it, so keep each parameter defined in one place only.

Before launching a campaign, paste the final tagged link into the UTM link tester to confirm every parameter reaches the landing page.

Back to Glossary