Developer

Base64 Encoder & Decoder

Convert between plain text and Base64 in either direction. Handles full UTF-8, the URL-safe variant, and works entirely in your browser — no uploads, no tracking.

URL-safe variant (base64url)

Plain text input

Base64 output

Conversion stats

Live counts update as you type.

Input characters

Output characters

Input bytes (UTF-8)

Output bytes

Size ratio

—

Output lines

Variant

Standard

Direction

Encode

What is Base64?

Base64 is a binary-to-text encoding that represents arbitrary bytes using a 64-character alphabet — uppercase A-Z, lowercase a-z, digits 0-9, plus `+` and `/`. It was designed for systems that only handle printable ASCII, so binary data like images, JSON tokens, or email attachments can travel through text-only channels unchanged. The output is about 33% larger than the input because every three bytes become four Base64 characters. This tool runs entirely in your browser using the standard `TextEncoder` / `atob` / `btoa` APIs, so nothing you paste leaves your device.

How to use the Base64 tool

1
Pick a direction
Choose encode to go from plain text to Base64, or decode to go from Base64 back to text.
2
Paste or type your input
Works with any UTF-8 text — emoji, non-Latin scripts, and multi-byte characters are all handled correctly.
3
Toggle URL-safe if needed
Tick the URL-safe checkbox to use the base64url alphabet (`-` and `_` instead of `+` and `/`) with padding stripped. Required for JWT tokens and many web APIs.
4
Copy the result
Click copy to grab the output, or click swap direction to feed the result back into the input with the opposite mode.

How Base64 works

Group the input into 3-byte blocks   (24 bits each)
Split each block into 4 groups of 6 bits
Map each 6-bit value (0–63) to the Base64 alphabet
 
Standard alphabet: A-Z a-z 0-9 + /
URL-safe alphabet: A-Z a-z 0-9 - _
 
Pad the last block with = until length is a multiple of 4
Output length = ceil(input_bytes / 3) × 4

Because 3 bytes equal 24 bits and 4 Base64 characters carry 24 bits of information, the encoding is lossless and exactly reversible. When the input length is not a multiple of three, the encoder pads the final group with `=` characters so every valid Base64 string is a multiple of four characters. The URL-safe variant defined in RFC 4648 §5 swaps the two characters that are reserved in URLs (`+` becomes `-`, `/` becomes `_`) and typically drops the padding, producing a form that can be pasted into a URL or a JWT without percent-encoding.

Reference: RFC 4648 — The Base16, Base32, and Base64 Data Encodings

Examples

Input	Output
"Hello, world!" → encode	SGVsbG8sIHdvcmxkIQ== Standard alphabet with two `=` padding characters.
"café ☕" → encode (UTF-8)	Y2Fmw6kg4piV Multi-byte characters are encoded as their UTF-8 bytes first.
c3ViamVjdHM_Zm9vJmJhcj0x → decode URL-safe	subjects?foo&bar=1 URL-safe variant uses `_` instead of `/` and drops padding.
aW52YWxpZA!!! → decode	Error `!` is not in the Base64 alphabet, so the tool reports an error.

Common use cases

Decode the header and payload sections of a JSON Web Token (JWT)
Inline images or fonts as data URIs in CSS or HTML
Transmit binary files through text-only channels like email or chat
Serialize credentials for HTTP Basic Authentication headers
Debug API requests that send binary bodies as Base64 strings
Encode a file for a quick copy-paste when file transfer is blocked
Read the contents of an encoded configuration value without writing a script
Convert a URL-safe token back to its original form for inspection

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Frequently asked questions

Is Base64 a form of encryption?

No. Base64 is encoding, not encryption — anyone can reverse it with the same kind of tool you are using now. Never use Base64 on its own to protect passwords, tokens, or private data. Use encryption (AES, RSA, etc.) for secrecy; Base64 exists purely to move binary data through text-only channels.

Why is the output always longer than the input?

Because Base64 represents every three bytes with four printable characters. That is a fixed 4/3 expansion, or roughly 33% larger. Short inputs are padded with `=` to keep the output a multiple of four characters, which can make the overhead a little higher for very short strings.

What's the difference between standard and URL-safe Base64?

The standard alphabet from RFC 4648 uses `+` and `/`, which both have special meanings inside URLs. The URL-safe variant (also RFC 4648) replaces them with `-` and `_`, and usually drops the trailing `=` padding. Use URL-safe Base64 for JWTs, query parameters, filenames, and anything else that might hit a URL parser.

Does this tool handle UTF-8 correctly?

Yes. Input is encoded to UTF-8 bytes before Base64 conversion, and decoded output is parsed as UTF-8. Emoji, accented characters, and non-Latin scripts all round-trip cleanly. The browser-native `btoa` function alone would fail on non-ASCII input, so this tool layers a UTF-8 step before calling it.

Why did decoding fail with an "invalid character" error?

The input contains characters outside the Base64 alphabet (letters, digits, `+`, `/`, `=`), or the padding is wrong. Copy-pasting from email clients sometimes introduces stray whitespace or quote marks — strip them and try again, or enable the URL-safe option if the string comes from a JWT or a URL.

Can I decode a JWT with this tool?

Yes, but you'll need to split the token by dots first. A JWT has three Base64url-encoded segments (header, payload, signature) separated by `.`. Paste each segment into the decoder with the URL-safe option enabled. The header and payload decode to JSON; the signature is raw bytes and will typically show as garbled characters.

Are there character-count limits?

There is no hard limit imposed by this tool, but the browser uses memory proportional to the input size. Pasting hundreds of megabytes can freeze the tab — for very large files, prefer a streaming encoder in Node.js or a command-line tool like `base64`.

Is anything stored or sent to a server?

Nothing is uploaded or logged. The encode and decode operations run entirely in your browser using the standard `TextEncoder` and `atob` / `btoa` APIs. Close the tab and the input is gone.

Last updated 2026-04-23

What is Base64?

How to use the Base64 tool

Pick a direction

Choose encode to go from plain text to Base64, or decode to go from Base64 back to text.

Paste or type your input

Works with any UTF-8 text — emoji, non-Latin scripts, and multi-byte characters are all handled correctly.

Toggle URL-safe if needed

Tick the URL-safe checkbox to use the base64url alphabet (`-` and `_` instead of `+` and `/`) with padding stripped. Required for JWT tokens and many web APIs.

Copy the result

Click copy to grab the output, or click swap direction to feed the result back into the input with the opposite mode.

How Base64 works

Group the input into 3-byte blocks   (24 bits each)
Split each block into 4 groups of 6 bits
Map each 6-bit value (0–63) to the Base64 alphabet
 
Standard alphabet: A-Z a-z 0-9 + /
URL-safe alphabet: A-Z a-z 0-9 - _
 
Pad the last block with = until length is a multiple of 4
Output length = ceil(input_bytes / 3) × 4

Examples

Input	Output
"Hello, world!" → encode	SGVsbG8sIHdvcmxkIQ== Standard alphabet with two `=` padding characters.
"café ☕" → encode (UTF-8)	Y2Fmw6kg4piV Multi-byte characters are encoded as their UTF-8 bytes first.
c3ViamVjdHM_Zm9vJmJhcj0x → decode URL-safe	subjects?foo&bar=1 URL-safe variant uses `_` instead of `/` and drops padding.
aW52YWxpZA!!! → decode	Error `!` is not in the Base64 alphabet, so the tool reports an error.

Common use cases

Decode the header and payload sections of a JSON Web Token (JWT)

Inline images or fonts as data URIs in CSS or HTML

Transmit binary files through text-only channels like email or chat

Serialize credentials for HTTP Basic Authentication headers

Debug API requests that send binary bodies as Base64 strings

Encode a file for a quick copy-paste when file transfer is blocked

Read the contents of an encoded configuration value without writing a script

Convert a URL-safe token back to its original form for inspection