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Encodeur Base64

Base64 encoding converts binary data (images, files, arbitrary bytes) into ASCII text using 64 printable characters. It is essential for embedding binary data in text-based protocols: HTTP headers, email attachments (MIME), JSON payloads, and data URLs in HTML/CSS. Our tool handles text-to-Base64, file-to-Base64, URL-safe Base64, and data URL generation.

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What is Base64?

Base64 is a encoding scheme that converts binary data into ASCII text format. It uses 64 safe characters to represent data, making it ideal for transmitting data across text-only channels.

Common uses include:

  • Encodage d'images en data URIs HTML/CSS
  • Encodage des identifiants en HTTP Basic Auth
  • Transfert de données binaires par e-mail ou API
  • Incorporer des fichiers binaires dans JSON ou XML
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À propos de Base64 Encoder / Decoder

Base64 encoding converts binary data (images, files, arbitrary bytes) into ASCII text using 64 printable characters. It is essential for embedding binary data in text-based protocols: HTTP headers, email attachments (MIME), JSON payloads, and data URLs in HTML/CSS. Our tool handles text-to-Base64, file-to-Base64, URL-safe Base64, and data URL generation.

Comment l'utiliser

  1. Enter text or paste binary data to encode to Base64.
  2. Paste a Base64 string to decode back to text or binary.
  3. Upload an image to generate a Base64 data URL (data:image/png;base64,...).
  4. Toggle between standard Base64 (uses + and /) and URL-safe Base64 (uses - and _).

Formule et méthodologie

Base64 encodes 3 bytes → 4 characters. Output size = ceil(input bytes / 3) × 4. Padding with = to make output length a multiple of 4. Character set: A–Z, a–z, 0–9, +, / (standard) or -, _ (URL-safe). Encoded size ≈ input size × 4/3 (+33%). btoa() and atob() in JavaScript; base64_encode() in PHP.

Cas d'usage courants

  • Embedding images directly in HTML/CSS without separate HTTP requests
  • JWT tokens: header and payload are Base64url encoded
  • API authentication: Basic Auth sends "username:password" as Base64
  • Email: MIME encoding for attachments (multipart/mixed)
  • Environment variables: storing binary secrets as Base64 in .env files

Questions fréquentes

Base64 represents every 3 bytes of binary data as 4 ASCII characters. 3 bytes × 8 bits = 24 bits; divided across 4 characters of 6 bits each = 24 bits. But each Base64 character is stored as 1 byte (8 bits), not 6. So 3 bytes become 4 bytes — a 33% increase. For this reason, inline Base64 images in CSS increase CSS file size by 33%, which can outweigh the benefit of saving an HTTP request.
Standard Base64 uses characters + and / which have special meaning in URLs (+ = space, / = path separator) — they must be percent-encoded in URLs. Base64url replaces + with - and / with _ and omits the = padding, making the output URL-safe without encoding. JWT tokens, OAuth codes, and web-safe file identifiers use Base64url. Always use Base64url when the encoded value will appear in a URL.

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