Does the Sigma 30mm f/1.4 work for both nikon and canon?

I saw an ad online for a "Sigma 30mm f/1.4 for Nikon." Does this mean it only works for Nikon cameras? As a third party brand, shouldn't it work for both Canon and Nikon?

No, generic lenses are built to be used on specific camera systems.

You need to buy a Pentax lens if you own a Pentax, same for Nikon, Canon, Panasonic, Olympus, etc.

There are NO universal mount lenses

Nope… Sigma makes lenses for Sigma, Nikon, Canon, Pentax (and maybe Sony, I'm not sure) cameras. They all have different mounts.

That one works for Nikon. You can buy other versions for Pentax, Canon and Sony.

In the days of MF, Tamron made their, 'Adaptall-2,' system where mounts were interchangeable, but even then, you had to make sure with most third-party lenses that you bought the one that fitted your camera.

A Nikon camera needs a Nikon mount, a Canon camera needs a Canon mount, it's as simple as that. You can't put Ford wheels on a Chevy.

Yes, if it says for Nikon, then it only works for Nikon.

As a third party brand, shouldn't it work for both Canon and Nikon? NO! Because Nikon and Canon's lens sizes(the bottom part where you mount it to the lens) are different