Decode encoded words from email Subject and From headers, or build your own – the RFC 2047 mechanism that lets ASCII-only headers carry any language.
Show calculation steps
Processed privately in your browser — nothing you paste is uploaded, logged or stored.
How to use the MIME Header Encoder and Decoder
- Paste an email header value, such as a Subject line containing encoded words.
- Set the direction. When encoding, choose B for mostly non-ASCII text or Q for mostly ASCII.
- Click "Convert header".
Frequently asked questions
Why do email headers need their own encoding?
Because the original mail standards allowed only 7-bit ASCII in headers. RFC 2047 defines "encoded words" – a wrapper naming a charset and an encoding – so that a Subject line can carry any language while remaining pure ASCII on the wire.
What is the difference between the B and Q encodings?
B is Base64, which suits text that is mostly non-ASCII. Q is a quoted-printable variant that leaves ASCII readable and escapes the rest, which suits mostly-Latin text with a few accents. Both are equally valid.
Why do adjacent encoded words join without a space?
It is a deliberate rule: whitespace between two encoded words is discarded, so that long text can be split across several words – each capped at 75 characters – without introducing spaces that were never in the original.
The charset in a header is not supported. What happens?
The tool falls back to UTF-8 and tells you, because the browser only decodes charsets it knows. The result may be wrong for an unusual legacy charset, and the note makes that explicit rather than hiding it.
