Question 1

Why do we encode text to Base64?

Accepted Answer

Base64 encoding lets you safely transmit arbitrary text or binary data over channels that only handle printable ASCII characters, such as HTTP headers, email (MIME), JSON fields, and data URIs in HTML/CSS.

Question 2

Why does Base64 increase the output size by about 33%?

Accepted Answer

Base64 encodes every 3 input bytes into 4 output ASCII characters. This 3-to-4 ratio means every block of 3 bytes becomes 4 characters, resulting in output that is approximately 33% larger than the original.

Question 3

What is the difference between standard and URL-safe Base64?

Accepted Answer

Standard Base64 uses + and / which have special meaning in URLs and must be percent-encoded. URL-safe Base64 replaces + with - and / with _ and omits = padding, so the string can be used directly in URLs, filenames, and query parameters. JWT tokens always use URL-safe Base64.

Question 4

What is the difference between UTF-8 encoding and ASCII encoding for Base64?

Accepted Answer

ASCII only covers 128 characters (0–127). UTF-8 is a superset that encodes all Unicode characters including Korean, Chinese, Japanese, emoji, and more. Using UTF-8 ensures non-ASCII text like 안녕 or 你好 is correctly converted to bytes before Base64 encoding.

Question 5

Where is Base64 encoding commonly used?

Accepted Answer

Common uses include: JWT token payloads (URL-safe), HTTP Basic Authentication headers, embedding images as data URIs in HTML, email MIME attachments, API authentication tokens, inline fonts in CSS, and encoding binary data inside JSON or XML.

Question 6

How do I decode a Base64 string back to the original text?

Accepted Answer

Use the companion Base64 to Text tool on this site. Paste the Base64 string, select Standard or URL-safe mode (or Auto-detect), and click Decode to retrieve the original text.

텍스트 → Base64