Why does decoding fail?

Wrong alphabet, corrupt Base64, data that is not gzip-wrapped, or UTF-8 that fails strict decoding.

Standard Base64 is expected; normalize URL-safe forms elsewhere if needed.

Use the regular Base64 decode tool; gzip decode expects compressed binary inside the Base64.

Data sent to a server?

No. Decompression runs locally.

Paste a Base64 string that wraps gzip-compressed data. The tool decodes Base64, decompresses gzip, then decodes UTF-8.

Base64 (gzip)

Text

Whitespace is stripped from the Base64 input, bytes are decoded, then the gzip stream is decompressed.

The result is interpreted as UTF-8 text with strict validation.

Unpack payloads from APIs, logs, or the matching encoder on this site.

Anyone with the Base64 string can recover the original. Treat decoded text like any sensitive content.

Why does decoding fail?: Wrong alphabet, corrupt Base64, data that is not gzip-wrapped, or UTF-8 that fails strict decoding.
URL-safe Base64?: Standard Base64 is expected; normalize URL-safe forms elsewhere if needed.
Plain Base64 text?: Use the regular Base64 decode tool; gzip decode expects compressed binary inside the Base64.
Data sent to a server?: No. Decompression runs locally.