Question 1

What is Base64 decoding?

Accepted Answer

Base64 decoding is the reverse of Base64 encoding. It converts a Base64 string (made up of A–Z, a–z, 0–9, +, /, and = padding) back into its original binary data or text. When the original content was UTF-8 text, decoding produces the human-readable string.

Question 2

How do I detect whether a Base64 string is standard or URL-safe?

Accepted Answer

Standard Base64 uses + and / characters and may end with = padding. URL-safe Base64 uses - and _ instead and typically omits padding. Auto-detect mode checks for the presence of - or _ to determine which variant to use.

Question 3

What happens when a Base64 string contains invalid characters?

Accepted Answer

Decoding will fail and an error is shown. Base64 only allows A–Z, a–z, 0–9, +, / (standard) or - and _ (URL-safe), and = for padding. Whitespace is stripped automatically, but other characters cause an invalid Base64 error.

Question 4

What is the difference between decoding Base64 text and Base64 binary data?

Accepted Answer

When decoding Base64 that represents UTF-8 text, the result is a readable string. When the original data was binary (e.g., an image or file), decoding produces raw bytes that cannot be displayed as text. This tool is optimized for text output using UTF-8 decoding.

Question 5

What are common use cases for Base64 decoding?

Accepted Answer

Common uses include: inspecting JWT token payloads, debugging API responses that contain Base64-encoded fields, reading email MIME attachment metadata, and verifying Base64-encoded credentials in Authorization headers.

Question 6

Why does Base64 decoding require padding characters (=)?

Accepted Answer

Base64 processes data in 4-character blocks. If the encoded string length is not a multiple of 4, padding = characters are added to make it so. During decoding, missing padding is automatically restored so the string can be decoded correctly.

Base64 → 텍스트