Base64 Encode / Decode

What is Base64 Encode / Decode?

Base64 is one of those things you run into constantly as a developer but rarely think about until you need to encode or decode something in a hurry. You get a Base64 string in an API response and need to see what's inside. You need to embed a small image directly in CSS. You're debugging a JWT token and want to read the payload. You're working with email headers that encode subject lines in Base64. This tool handles all of that instantly.

AllKit's Base64 encoder and decoder works in both directions: paste plain text to get Base64, or paste Base64 to get the original text back. It fully supports UTF-8, so you can encode text in any language — Chinese, Arabic, emoji, special characters — and it all round-trips correctly. It also supports URL-safe Base64 (using - and _ instead of + and /) which is commonly used in JWT tokens, URL parameters, and file names.

The tool handles large inputs efficiently because everything runs in your browser using native JavaScript APIs. There's no server involved, no file size restrictions from an upload endpoint, and no waiting for network roundtrips. Paste a massive Base64 string from a data URI and see the decoded result instantly.

Security matters when you're encoding and decoding data. Because this tool runs entirely client-side, your data never touches a server. This makes it safe for decoding Base64 strings that contain sensitive information like API keys, tokens, encoded credentials, or personal data. You're not sending your secrets to some random server to decode them.

Why use AllKit?

• No ads, no distractions — a clean interface that lets you focus on the task
• Privacy-first — 100% client-side processing, nothing is uploaded
• Free forever — core tools are free with no usage limits
• API available — integrate into your workflow via our REST API

How to Use Base64 Encode / Decode

1. Choose your mode: Encode (text to Base64) or Decode (Base64 to text). The default is Encode.
2. Paste or type your input in the top text area. For encoding, enter the plain text you want to convert. For decoding, paste the Base64 string.
3. The result appears instantly in the output area below. There's no need to click a button — the conversion happens in real time as you type.
4. Use the URL-safe toggle if you need Base64 that's safe for URLs and filenames. This replaces + with - and / with _ in the output, which is required for JWT tokens and URL parameters.
5. Click the Copy button to copy the result to your clipboard. A brief confirmation appears to let you know it worked.
6. To swap directions (decode what you just encoded, or vice versa), click the swap button to flip the input and output.
7. For file encoding, you can paste the content of binary files as text. For image embedding, the output gives you a data URI you can use directly in HTML or CSS.

Common Use Cases

Technical Details

Base64 encoding maps every 3 bytes of input to 4 ASCII characters using a 64-character alphabet: A-Z, a-z, 0-9, + and /. The = character is used for padding when the input length isn't a multiple of 3. This means Base64 output is always exactly 4/3 the size of the input (about 33% larger).

URL-safe Base64 (also called Base64url, defined in RFC 4648) replaces + with - and / with _ to avoid conflicts with URL syntax. It optionally omits the = padding. This variant is used in JWTs, many OAuth implementations, and anywhere Base64 data appears in URLs.

The tool uses the browser's native btoa() and atob() functions for ASCII content, with a TextEncoder/TextDecoder wrapper for full UTF-8 support. This means encoding and decoding is handled by optimized browser engine code, not a JavaScript library, so it's extremely fast.

For UTF-8 content, the encoding process first converts the string to a UTF-8 byte sequence, then Base64-encodes those bytes. Decoding reverses the process. This correctly handles multi-byte characters including emoji (which are 4 bytes in UTF-8), CJK characters, accented letters, and any Unicode content.