What is Base64?
Base64 is a method for encoding binary data into text.
It is commonly used to represent data in formats that only support plain text, such as JSON, XML, HTTP headers, and email.
Base64 is not encryption and does not provide confidentiality.
Its purpose is to make binary data safe to transmit or store in systems that expect text.
Why Base64 exists
Many systems were originally designed to handle text only.
Binary data (such as images, files, or cryptographic material) can become corrupted when passed through systems that:
- Expect ASCII or UTF-8 text
- Modify or filter certain byte values
- Are not binary-safe
Base64 solves this by converting binary data into a restricted set of printable characters that are widely supported.
How Base64 works (conceptually)
At a high level, Base64 works by:
- Taking binary data (bytes)
- Grouping the data into chunks of 3 bytes (24 bits)
- Splitting those 24 bits into 4 groups of 6 bits
- Mapping each 6-bit value to a printable character
This mapping uses a fixed alphabet of 64 characters, which is where the name “Base64” comes from.
The Base64 character set
The standard Base64 alphabet consists of:
- Uppercase letters:
A–Z(26) - Lowercase letters:
a–z(26) - Digits:
0–9(10) - Two symbols:
+and/
That gives a total of 64 possible characters.
Padding in Base64 (=)
Because Base64 processes data in fixed-size blocks, the encoded output may include one or two = characters at the end.
Padding is used to:
- Signal the end of the original data
- Ensure the encoded output length is a multiple of 4 characters
Padding does not add information — it only ensures correct decoding.
Common Base64 use cases
Base64 is widely used in modern software and infrastructure.
APIs and web services
Binary data is often embedded in JSON or XML payloads using Base64 encoding.
Examples include:
- File uploads
- Binary configuration data
- API request/response bodies
Data URLs
Base64 can be used to embed small files directly into HTML or CSS.
For example:
- Inline images
- Embedded fonts
This avoids additional HTTP requests but increases payload size.
Email (MIME encoding)
Email systems historically support only text content.
Base64 is used to encode:
- Attachments
- Non-ASCII message content
Tokens and authentication
Base64 is commonly used inside authentication mechanisms such as JWT (JSON Web Tokens).
In these cases:
- The token structure is text
- The payload may represent binary or structured data
Base64 is not encryption
A common misconception is that Base64 provides security.
It does not:
- Protect data from being read
- Hide or obfuscate information
- Provide integrity or authenticity
Anyone can decode Base64 without a key.
Base64 should be treated as a transport encoding, not a security mechanism.
Standard Base64 vs URL-safe Base64
Standard Base64 uses the characters + and /, which can cause issues in URLs and filenames.
URL-safe Base64 replaces these characters:
+→-/→_
Padding may also be omitted.
URL-safe Base64 is commonly used in:
- URLs
- JWT tokens
- Web APIs
When to use Base64
Base64 is appropriate when:
- You need to transmit binary data through text-only systems
- Compatibility is more important than efficiency
- You understand the size overhead (Base64 increases size by ~33%)
Base64 is not appropriate when:
- You need encryption or secrecy
- Bandwidth or storage size is critical
- Binary-safe alternatives are available
Using Base64 safely
When working with Base64:
- Treat encoded data as public
- Avoid assuming secrecy
- Validate and decode input carefully
- Prefer local, client-side tools when handling sensitive data
Safe64 performs all Base64 encoding and decoding locally in your browser, without sending data to a server.
Summary
Base64 is a simple and widely used encoding technique that enables binary data to be represented safely as text.
It plays an important role in:
- Web APIs
- Cloud infrastructure
- Authentication systems
- Email and data transport
Understanding what Base64 does — and what it does not do — helps avoid common mistakes and security misunderstandings.