Embedding small binary data inside text-only formats: data URIs, JSON values, environment variables, YAML strings. Encoding binary tokens (signatures, keys, hashes) for inclusion in URLs, headers, or cookies. Email attachments and SMIME — historic but still alive.

Don't confuse it with encryption. Base64 is reversible by anyone. If the data is sensitive, encrypt it first. UTF-8 round-trips correctly here — non-ASCII (é, 你好, 🚀) goes through TextEncoder / TextDecoder , not btoa / atob directly. Naive btoa(str) in JavaScript breaks on non-Latin characters. Padding — standard Base64 always ends with 0/1/2 = characters depending on input length. base64url often omits them. Decoders that require padding will reject unpadded input; this tool re-adds it on decode if missing. Whitespace inside encoded strings — the decoder here strips spaces and line breaks (common from copy-paste), but some libraries don't, so re-encode if you're piping to one of those.

Encodeur / Décodeur Base64

Encodez du texte en Base64 ou décodez du Base64 en texte. UTF-8 et variante base64url supportées.

Mode

Variant

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What Base64 actually does

Base64 turns arbitrary bytes into 64 ASCII characters (A–Z, a–z, 0–9 plus two extras). Three input bytes become four output characters, so the result is roughly 33% larger than the input. It's an encoding, not encryption — anyone can decode it.

When to use Base64

Embedding small binary data inside text-only formats: data URIs, JSON values, environment variables, YAML strings.
Encoding binary tokens (signatures, keys, hashes) for inclusion in URLs, headers, or cookies.
Email attachments and SMIME — historic but still alive.

Standard vs base64url

Standard (RFC 4648 §4) uses +, /, =. Fine in email, JSON values, most XML.
base64url (RFC 4648 §5) uses -, _, and typically drops trailing = padding. Used in JWTs, OAuth tokens, and anywhere the value lives in a URL where +///= would need extra escaping.

Common gotchas

Don't confuse it with encryption. Base64 is reversible by anyone. If the data is sensitive, encrypt it first.
UTF-8 round-trips correctly here — non-ASCII (é, 你好, 🚀) goes through TextEncoder/TextDecoder, not btoa/atob directly. Naive btoa(str) in JavaScript breaks on non-Latin characters.
Padding — standard Base64 always ends with 0/1/2 = characters depending on input length. base64url often omits them. Decoders that require padding will reject unpadded input; this tool re-adds it on decode if missing.
Whitespace inside encoded strings — the decoder here strips spaces and line breaks (common from copy-paste), but some libraries don't, so re-encode if you're piping to one of those.