I'm not coming up with anything by searching; does anyone know?
Many WGs are done on the basis of mündlicher Vertrag. I have heard that there is then some letter that the WG host could sign and give to you to give to the Gemeinde, just basically saying "yeah that person lives here".
Verbal contracts are dodgy, but that's another story.
When I first moved here and stayed in a friends spare room, he wrote a statement along the lines of "ATO moved here on the DD.MM.YY" and scribbled a signature on it. That was accepted.
"Ask the Gemeinde" could be the best solution though to be sure.
Yep, this is common, that a letter is drafted for Migrationsamt identifying the person, and saying very simply that the person is living at the address, from what date, and whether an end-date has been agreed, or not.
The person writing the letter details their status, as the main renter (the person who signed the contract with the owner), or 1 of the main renters (if more than 1 signed the contract with the owner).
Be prepared in case there's a little back-and-forth. I've known a very recent example of someone taking the letter to Migrationsamt, and it being refused, only for them to go back the next day with the very same letter, encounter someone different at the counter, and for everything to be accepted.
In Zurich the owner or main tenant has 14 days to announce your residence. They can do this online here or download the snail mail form here Click on "Einzugsanzeige Stadt Zürich (PDF, 1 Seite, 1 MB)" (Assuming you're in Zurich City)
Yeah I should have specified. My case is the same as the one yiu describe, where it's a trusted friend's spare room and it's not worth making a contract.
As soon as they write you a letter for the gemeinde, you have a contract
It is always worth making a contract. It is easy enough to do. A contract has the great advantage of setting down what you're agreeing, clearly, so there are no misunderstandings. And it helps each party to know, clearly, what the procedure is when one or the other side decides to leave the contract. In the case of a WG, this can be particularly useful of one party is leaving, but the other wishes to stay, and a new agreement is needed with the new people.
Source: experience.
I've had various living people with us. A letter to the Gemeinde stating that that's where they live and from when, signed by owner/principle renter is sufficient.
And you can download simple examples easily
e.g. the Untermietvertrag here: https://www.mieterverband.ch/mv/miet...am-wohnen.html
Just two pages, mostly tickboxes.