Is it safe to use an old Altoid mint tin as a nest for a parakeet?

I wouldnt use that. Now how large is the tin exactly? Budgies and other parakeets dont like open nests. They like to have a dark place with walls around them.

You can easily make a nest box at home or buy one from the store. They only cost about $10.

 

There is no need for the tin whatsoever with the nestbox. I know you mean well and want to help the birds out but they are quite capable of building the nest themselves. Simply put bedding into the box and they will do their thing. You dont want to risk metal poisoning either!!!

 

Budgies, like virtually all other species of parrots, don't build nests. In the wild, they seek out hollows in trees, or the previously-used nests of other species. Lovebirds will bring some material to the nests for bedding, Quakers will actually build colonial nests out of twigs, but they're about the only exceptions.

Are you intending to breed them? Because this is what "providing a nest" will stimulate. If you're not set up to breed and raise babies, don't offer a nestbox.