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Great question! When you see base64 string, one way you can tell is if there are 1-3 equal ‘=‘ signs on the end, and this is padding. Ex. a2e771gafs==. This is because all base64 string is usually divisible by 4, and the padding is added so that it can be divisible by 4 properly. For example, the string above is divisible by 4 with the padding: a2e7, 71ga, fs==. Most of the time though base64 decoders don’t need this padding, but if you’re really unsure of what type of string it is, you can put it in a cipher text identifier and it’ll tell you it’s base64, for instance the CyberChef ‘Magic’ option can do that for you. But for me, I can just kinda tell right away because I’ve seen base64 so many times.