Base64 and URL encoding: Unicode examples and decoding errors

Pick the mode for the job

Open the encoding tool (Chinese interface). Base64 mode encodes UTF-8 text. URL mode encodes a parameter value, including spaces and reserved characters. The output of one mode is not automatically valid input for the other.

Round-trip Unicode text

Select Base64, enter 有界 and encode. The expected result is 5pyJ55WM. Swap the result into the input and decode to recover the original characters. This example has been checked against the current implementation. The tool handles text; it is not a general binary-file viewer.

Encode a URL parameter

In URL mode, enter 有界 AI/a+b. The expected output is:

%E6%9C%89%E7%95%8C%20AI%2Fa%2Bb

Space becomes %20, while the slash and plus sign are escaped too. Decoding should restore the input exactly. Encode individual parameter values before assembling a URL; encoding a complete address does not produce an equivalent navigable URL.

Understand decoding failures

The string !!!! is invalid Base64. The value /w== represents a byte that cannot be decoded as valid UTF-8 text and is rejected. An incomplete URL escape such as %E4 also fails. Inspect the source format and completeness instead of deleting characters until an error disappears.

Plus signs and confidentiality

URL decoding follows decodeURIComponent behavior: a literal plus sign is not converted to a space. Form encoding may require different handling. Base64 does not conceal secrets from someone who can decode it. Processing stays in the browser, but copied output can still contain information that should not be shared.