What is RFC 2047 Q-encoding?

RFC 2047 lets non-ASCII text appear in email headers by wrapping it in an encoded-word: =?charset?Q?text?=. The Q variant is a header-specific form of quoted-printable where each non-ASCII byte becomes an equals sign followed by two hex digits, and spaces become underscores.

How does Q-encoding differ from quoted-printable?

Q-encoding is based on quoted-printable but adds header-specific rules: a space is encoded as an underscore, and the characters question mark, underscore, and equals sign are always escaped because they have structural meaning inside an encoded-word.

When should I use Q-encoding versus B-encoding?

Q-encoding stays mostly readable when the text is largely ASCII with a few accented characters, so it is efficient for European-language subjects. B-encoding (Base64) is more compact when most of the text is non-ASCII, such as Chinese or Arabic.

What is the maximum length of an encoded-word?

RFC 2047 limits a single encoded-word to 75 characters including the charset, delimiters, and encoding marker. Longer values must be split into multiple encoded-words separated by whitespace; this tool flags when output exceeds that limit.

Is anything sent to a server?

No. Encoding and decoding happen entirely in your browser with JavaScript, so email content and recipient names never leave your device.

Q-Encoding (RFC 2047) Encoder

RFC 2047 Q-encoding is how non-ASCII text — accented names, emoji, other scripts — is safely placed in email headers such as Subject and From. It wraps the text in an encoded-word: =?UTF-8?Q?...?=. This tool encodes and decodes Q encoded-words in your browser.

How it works

The encoded-word format is =?charset?encoding?encoded-text?=. For the Q encoding:

The text is first converted to UTF-8 bytes with TextEncoder.
Printable ASCII bytes pass through unchanged, except that space becomes _, and =, ?, and _ are always escaped because they are structural.
Every other byte (any byte over 0x7E, control characters, and the escaped ones) becomes = followed by two uppercase hex digits — for example é (UTF-8 0xC3 0xA9) becomes =C3=A9.
The result is wrapped as =?UTF-8?Q?...?=.

Decoding reverses this: it reads the charset and Q marker, turns _ back into a space, and converts each =XX back into its byte before UTF-8 decoding.

Tips and examples

The subject Café encodes to =?UTF-8?Q?Caf=C3=A9?=. A space-separated phrase like Re: déjà vu becomes =?UTF-8?Q?Re=3A_d=C3=A9j=C3=A0_vu?= — note the ?-equivalent colon escaping and the underscore for the space. Keep each encoded-word under 75 characters; the tool warns you when a value is long enough that a real mail client would need to split it across multiple encoded-words.