You send paid or partner traffic through a redirect and you want every click to arrive at the destination carrying its own identifier — something to join against a conversion later. The obvious tool is a Worker, and for anything that needs to record the click, a Worker is still the only primitive that can. But if all you need is for each click to carry a unique id, there is a way to get one on the free plan, inside a plain Single Redirect, with no code in the request path at all.
We tested it on this site's zone on 30 July 2026. It works, and three of its edges bite. Here is the rule, the measurements, and the traps.
The function that is banned, and the field that is not
The ruleset expression language has uuidv4(). You cannot use it here. The documentation restricts it to rewrite expressions of Transform Rules, and the API enforces that at validation time. This is the live answer to an attempt to put it in a redirect target:
"'concat(\"https://301.sh/?click_id=\", uuidv4(cf.random_seed))' is not a valid
