Decode Base64 strings back to readable plain text. Base64 is a reversible encoding (not encryption) used in APIs, email attachments, JWT payloads, and data URLs.
How decoding works
Each group of four Base64 characters represents three original bytes. Padding symbols (=) at the end indicate how many bytes were present in the final incomplete group. This tool validates the alphabet and padding, then outputs UTF-8 text when the underlying bytes represent valid Unicode.
Common use cases
- Inspecting Base64 fields returned by REST or GraphQL APIs
- Recovering text from
data:URLs or configuration snippets - Verifying that an encoder produced the expected output (round-trip testing)
- Reading the payload section of a JWT before signature verification elsewhere
Limitations
Decoding arbitrary Base64 may produce non-printable or invalid UTF-8 bytes if the original data was binary (images, compressed files). This tool targets text payloads. Invalid characters, wrong padding, or truncated strings will fail decoding. Base64 decoding reveals content to anyone with the string—it does not protect secrets.
Example
SGVsbG8= decodes to Hello. Whitespace in pasted input is typically ignored; only characters from the Base64 alphabet are processed.