Base64Fix.ai — Base64 Repair Tools
Fix Broken Base64 Padding Instantly
Missing or incorrect Base64 padding (the = characters) is one of the most common Base64 errors. Fix it automatically.
What Is Base64 Padding?
Base64 encodes 3 bytes at a time into 4 ASCII characters. When the input length is not a multiple of 3, the output is padded with = characters to make the encoded length a multiple of 4.
| Input bytes | Padding needed | Example |
|---|---|---|
| Multiple of 3 (e.g., 6) | None | SGVsbG8h |
| 1 extra byte | == | SQ== |
| 2 extra bytes | = | SGk= |
Why Padding Goes Missing
- →URL-safe Base64 (RFC 4648 §5) strips padding — because = is a reserved URL character.
- →Some APIs and libraries strip trailing = when transmitting Base64 (e.g., in HTTP headers or JSON payloads).
- →JWT tokens use URL-safe Base64 without padding by design.
- →Copy-paste truncation: the = at the end gets cut off accidentally.
How Base64Fix.ai Fixes Padding
// Auto-pad logic (runs client-side in your browser)
function fixPadding(base64: string): string {
const stripped = base64.replace(/=/g, "");
const mod = stripped.length % 4;
if (mod === 2) return stripped + "==";
if (mod === 3) return stripped + "=";
return stripped; // mod === 0: no padding needed
}The algorithm calculates the correct number of = characters needed and adds them before decoding. This happens entirely in your browser — no data is sent to a server.
Fix Base64 Padding — Free & Instant
Paste broken Base64 and we'll fix the padding automatically.
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