Recognising base64-encoded JSON

If you see a chunk of text beginning with eyJ, it’s probably base64-encoded JSON. Here’s a demonstration.

Commonly when dealing with various APIs, you’ll be confronted with base64-encoded data. If the base64 encoding starts with eyJ, you can be pretty sure that it’s base64-encoded JSON.

Here’s a demonstration:

% echo '{"a' | base64
eyJhCg==
% echo '{"z' | base64
eyJ6Cg==
% echo '{"A' | base64
eyJBCg==
% echo '{"Z' | base64
eyJaCg==

Essentially, if the text begins with {", then any ASCII character in the range 64-127 (that’s upper- and lower-case A-Z, plus a few bits of punctuation), it’ll encode starting with eyJ. Since JSON keys are strings, and are almost always alphabetic, this is what you’ll most commonly see.