Base64 Encoder / Decoder
About this Tool
AllThatConverter's Base64 encoder and decoder is the most popular free online tool for converting text and data to and from Base64 format. Base64 is essential for email attachments, REST API payloads, data URI image embedding, and much more. All processing runs entirely in your browser with no server uploads, so sensitive data stays private. Both standard Base64 and URL-safe Base64url (RFC 4648) are supported. No registration required, completely free.
Processed safely on your device
Everything happens in your browser on this device. Your files are never sent to our servers—so you can use it with peace of mind.
How to Use
Paste the text you want to encode or decode into the input area.
Click 'Base64 Encode' or 'Base64 Decode'.
The converted result appears instantly in the output area.
Click 'Copy' to save it to your clipboard.
Key Scenarios & Use Cases
Inline Image Data URIs
Embed images directly into HTML or CSS as Base64 data URIs, eliminating external file references for email templates or offline pages.
Web APIs and JWT Authentication
Base64 encoding is standard in REST API request bodies, headers, and JWT token payloads.
Email MIME Attachments
The MIME email protocol encodes binary file attachments in Base64 for transmission — this tool helps troubleshoot and verify them.
Config Files and Environment Variables
Safely embed certificates or values containing special characters in config files and environment variables using Base64.
Frequently Asked Questions (FAQ)
Standard Base64 uses + and /, which have special meaning in URLs. Base64url (RFC 4648) replaces + with - and / with _ for safe use in URLs and filenames.
Base64-encoded data is approximately 133% the size of the original — 3 bytes become 4 Base64 characters.
No. All processing runs locally in your browser. Your input never reaches any external server.
Yes. Multibyte characters are first converted to UTF-8 bytes, then Base64-encoded. Decoding reverses the process correctly.