Base64URL Decoder Online
Restore readable text from a Base64URL value, including strings that omit trailing padding. This decoder checks the URL-safe alphabet and the encoded bytes before displaying the message. Paste a single value, convert and inspect the result without executing any decoded content.
- Decode padded and unpadded values
- Check canonical padding and unused bits
- Reject invalid UTF-8 instead of replacing bytes
Decode a known example first
Paste SGk or SGk= and convert; both produce Hi. Whitespace around the complete input is trimmed, but spaces inside the encoded value are rejected. The example field contains an encoded greeting with an emoji so you can also check a UTF-8 round trip. The output remains plain text even when the decoded content resembles HTML, JSON or a link.
Check the alphabet and padding
URL-safe Base64 uses letters, digits, hyphen and underscore, followed optionally by equals signs. Standard plus and slash characters are rejected here; use Base64 Decoder for that alphabet. The decoder restores missing padding only when the length permits it. It also rejects incorrect explicit padding and nonzero unused pad bits rather than silently accepting several noncanonical spellings of the same bytes.
Distinguish text from binary data
A correctly encoded Base64URL string can represent any bytes, but this tool is a text decoder. If the recovered bytes are not valid UTF-8, conversion stops with a message instead of substituting replacement characters. A signature, compressed file or image may therefore be valid Base64URL and still fail the text check. This is an encoding mismatch rather than proof that the original data is corrupt.
Handle token fragments carefully
A full JWT contains segments separated by dots and cannot be pasted as one Base64URL value. Use JWT Decoder to inspect the header and payload together, or paste a single text segment here. Decoding alone establishes no authenticity. Inputs are limited to 100,000 characters; check whether your source is truncated if its final group or padding repeatedly fails validation.
Technical references: Base64URL decoding and canonical encoding