What is Base64 and what is it for?

Base64 represents binary data using 64 printable ASCII characters. Used to send binaries through text-only channels: emails, JSON, URLs and data URIs.

Is Base64 encryption?

No. Base64 is just an encoding, reversible by anyone. If you need confidentiality, use real encryption (AES, libsodium, TLS).

When should I use URL-safe Base64?

When the result goes into URLs, HTTP headers or filenames. It replaces + with -, / with _ and skips the = padding, avoiding escaping.

How much does encoded text grow?

Roughly 33% larger. Every 3 bytes of input become 4 output characters.

Online Base64 Encoder

What Base64 is

Base64 is an encoding scheme that represents binary data using 64 printable ASCII characters: A-Z, a-z, 0-9, + and /, plus = as padding. Every 3 bytes (24 bits) map to 4 characters of 6 bits each. The name comes from "base 64": the system uses 64 symbols instead of the 256 possible in raw binary.

It's standardized in RFC 4648. There are variants: standard (with + and /), URL-safe (with - and _) and a few less common ones. Every serious language ships Base64 in its standard library.

When to use Base64

Email attachments. SMTP was designed for ASCII text. MIME uses Base64 to embed binaries (PDF, images) in messages.
Data URIs. data:image/png;base64,iVBORw0KGgo... embeds small images directly into HTML or CSS.
JSON with binary data. JSON only supports text. To send bytes without a multipart endpoint, encode them in Base64.
JWT. Header, payload and signature are encoded in URL-safe Base64.
Basic Auth. The Authorization: Basic ... header carries username:password in Base64 (not secure: requires HTTPS).
Config variables. To store small binaries (SSH keys, certificates) in environment variables or YAML.

The URL-safe variant

In URLs, + and / have special meaning. / separates path segments; + in query strings is interpreted as a space. To avoid escaping, the URL-safe variant replaces them with - and _. It also typically drops the trailing = padding.

This variant is used in JWT, OAuth (PKCE), public API keys and, in general, any token that ends up in a URL.

Size and efficiency

Base64 inflates data by about 33%: every 3 bytes become 4. A 100 KB image becomes 133 KB when Base64-encoded. That's why you should only embed small images as data URIs: for anything larger, serve them as a separate file.

If you need something even more compact, consider Base85 (Ascii85), which encodes 4 bytes in 5 characters (25% overhead). The PDF format uses it for embedded images.

Common Base64 mistakes

Confusing it with encryption. Base64 is readable — anyone can decode it. If you need privacy, encrypt with AES before encoding.
Forgetting UTF-8. For text with accents or emoji, encode to UTF-8 first (which our generator does), never plain ASCII.
Mixing variants. Decoding URL-safe Base64 with a standard decoder fails. Normalize first.
Missing padding. Some decoders require the trailing =. If your string lacks it, add it manually so the length is a multiple of 4.

Privacy of this encoder

Everything is processed in your browser with btoa on top of TextEncoder. No server, no content analytics, no logs. Paste whatever you want: if you close the tab, it goes with you.

Base64 Encoder