ConverterBase64 Decode
Decode a declared RFC 4648 alphabet back into bytes. Choose strict UTF-8 text when the bytes are text, or hexadecimal when they are binary or invalid UTF-8.
Decode Base64 Into Bytes
Strict Decoder Policy
| Input condition | Behavior |
|---|---|
| Outer whitespace | Trimmed |
| Internal whitespace | Rejected |
| Missing terminal padding | Accepted when byte length is possible |
| Wrong alphabet | Rejected |
| Non-canonical trailing bits | Rejected |
| Invalid UTF-8 in text mode | Rejected; use hex mode |
Bytes Are Not Automatically Text
A successful Base64 decode restores bytes. It cannot prove which text encoding created those bytes, whether the content is safe to render, or whether it is trustworthy.
Hexadecimal mode exposes each byte without inserting replacement characters. UTF-8 mode uses fatal decoding so malformed byte sequences cannot become misleading text.
Inspect Before Reuse
- Confirm the expected alphabet and padding policy.
- Treat decoded markup, tokens, and control characters as untrusted data.
- Do not publish secrets simply because decoding happens in the page.
Questions About This Tool
Base64 can represent arbitrary bytes. Those bytes may be binary data or text in another encoding rather than valid UTF-8.
No. This profile reconstructs terminal padding when the unpadded length can represent complete bytes, then checks canonical trailing bits.
No. Decoding changes representation; trust, sanitization, and validation remain separate.