Base64 — Encode and Decode Without Leaving the Browser
Base64 turns arbitrary bytes into text that survives being put somewhere that only accepts text — an HTTP header, a JSON string, a URL, an email body. It is not encryption and it is not compression; it makes data about a third larger and completely readable to anyone who decodes it, which is a distinction worth being clear about because a surprising amount of code treats it as though it were a security measure.
When it helps
You reach for it constantly once you notice. Basic authentication headers are Base64. Data URIs embedding a small image are Base64. JWT segments are Base64url, a variant with different padding. Docker registry credentials, Kubernetes secrets and a great many API callbacks all pass data this way, and when something is failing the first useful step is usually to decode it and confirm it contains what you think it contains rather than an error message or an empty string.
Worth running automatically
The manual case is one-off decoding, but the same operation belongs in an automated check whenever a value is embedded rather than referenced. A monitored endpoint that returns a Base64 payload can be verified for content rather than just a 200 status, which catches the case where the service is healthy and returning an encoded error. If you inline assets as data URIs, tracking their size over time is worthwhile too, because the third of extra weight is easy to forget and compounds quietly as more get added.
What you get out of it
Instant visibility into any of the many places the web hides bytes inside text. Most of its value is confirming that a value you cannot read is actually the value you expect, which is otherwise guesswork.