Normes Base64

Publié 11 octobre 2026

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This standards reference on Base64Encoding explains standards in plain language for developers and everyday users.

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“Base64” is a family of encodings. They all share the same 3-bytes-to-4-characters algorithm but differ in the last two alphabet characters, padding, line wrapping and extra framing.

Standard	Chars 62/63	Padding	Line length	Used in
Standard (RFC 4648 §4)	`+` `/`	required	none	APIs, JSON, data URIs
MIME (RFC 2045)	`+` `/`	required	max. 76	E-mail attachments
PEM (RFC 7468)	`+` `/`	required	exactly 64	Certificates, keys
Base64URL (RFC 4648 §5)	`-` `_`	optional	none	URLs, JWT, file names
IMAP (RFC 3501)	`+` `,`	none	none	Mailbox names in modified UTF-7
XML name token / identifier	`.` `-` / `_` `:`	none	none	XML `NMTOKEN` and `Name` values
OpenPGP armor (RFC 4880)	`+` `/`	required	max. 76	PGP messages, with CRC-24 checksum

Not sure which one you have? Use the standard detector, then convert between them with normalization.

Standard Base64 The standard Base64 encoding defined in RFC 4648 section 4: alphabet, mandatory padding, no line breaks, canonical encoding and validation regex. Base64URL What Base64URL is, how it differs from standard Base64 (- and _ instead of + and /, no padding), where it is used (JWT, URLs) and how to convert between them. MIME Base64 Base64 Content-Transfer-Encoding for e-mail as defined in RFC 2045: 76-character lines, CRLF line endings, ignored characters and how attachments are encoded. PEM What the PEM format is: Base64-encoded DER data between -----BEGIN----- and -----END----- lines, 64-character line wrapping, common labels and conversion. IMAP How IMAP mailbox names use a Base64 variant with + and , (RFC 3501 modified UTF-7). Alphabet, no padding, and how to decode IMAP Base64 online. XML XML Base64 variants for NMTOKEN (. -) and Name (_ :) values. How they differ from RFC 4648 and when to use them in XML documents. OpenPGP OpenPGP ASCII armor wraps Base64 in BEGIN/END headers with a CRC-24 checksum. How it differs from MIME Base64 and how to decode armored messages online.

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