I went to an ent yesterday and he told me i had a tonsil cyst which was nothing to worry about. can he tell by just looking?

Yes: Tonsils are very easily visualized by a qualified ENT physician. The question comes down to whether you are symptomatic - pain, trouble swallowing, hoarseness. If any if these are the case, it is unlikely that this is a simple cyst and you should seek additional information. But if the ENT was confident and you have trust in their assessment, then you need go no further for a tonsillar cyst.

Yes: A trained ENT will be able tell that a lesion on the tonsil

Mostly: A tonsil cyst is pretty easy to see just by looking, or even easier with a simple X-Ray.There are SO many important things in the neck area, you don't want to wait too long before something gets infected--the swelling could make it difficult to breathe pretty quickly. It really depends on how big it is, and how irritated it is. So, things to keep in mind is if you have diff.breathing, or more pain