Base64 Padding Explained: Why = Characters Appear at the End
Understand Base64 padding: why = signs appear, when you get one vs two, and when it's safe to strip them in URL-safe variants.
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Tags: encoding, developer-tools, base64
Base64 Padding Explained: Why = Characters Appear at the End If you've ever looked at a Base64 string and wondered why it ends with one or two equals signs, those are padding characters — and they exist because of a fundamental mismatch between input and output sizes. This post explains exactly why appears, when you get zero, one, or two of them, and how to handle padding in real-world code. The Root Cause: 3 Doesn't Divide 8 Evenly Base64 encodes 3 input bytes as 4 output characters. Every 3 bytes maps cleanly to 4 characters. But real data isn't always a multiple of 3 bytes long. When the input length mod 3 is non-zero, you have a partial final group. The padding character fills that partial group to maintain the invariant that Base64 output length is always a multiple of 4. The three…
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