Johnny B Good wrote:

How can I recognise the junk parts of a url like that? I can see that I
need to keep the "https://www.ebay.co.uk" bit

for eBay you can lose the www. as well if you like

and also the need to
include the "263383424663" unique item code but how did you translate the
"/itm/HP5100i-Inverter-Generator-Petrol-Generator-with-Battery-Key-
Starter-generator/" into "/genny/"?

anything between /itm/ and /theitemnumber
is pure search engine fodder, you can chop it all out for the absolute
shortest

https://ebay.co.uk/itm/263383424663

or replace it with anything you like

https://ebay.co.uk/itm/anything-you-like/263383424663

The same sort of tricks work for toolstation and screwfix, and many but
not all newspaper sites ...

I keep meaning to put up a website that will strip a URL to the bones,
but leave it pointing to the original site, as an alternative to using a
redirection shortening site like tinyurl.