#488 · Developer Tool

MIME Encoded Word Decoder

Decode RFC 2047 MIME encoded-words in email header values, supporting UTF-8 and ISO-8859-1 with both Base64 and Q encodings. Processing stays in the browser, so the input is not sent to a conversion service.

Developer Input

MIME header value
Ad space

How to use this developer tool

  1. Paste mime header value or load the sample.
  2. Choose any format-specific option shown above the run button.
  3. Select Decode Header Words or press Ctrl/Cmd + Enter.
  4. Review the summary and download the result if it matches your target format.

What this developer tool does

It replaces each valid encoded-word while leaving surrounding plain ASCII header text in place.

The form =?charset?B?...?= uses Base64; =?charset?Q?...?= uses quoted-printable rules where underscores represent spaces.

Adjacent encoded-words separated only by whitespace are joined as required for folded header text.

Example

Input

Subject: =?UTF-8?Q?Caf=C3=A9_updates?= =?UTF-8?B?4pyT?=

Run the included sample to see the exact output and byte statistics produced by the current options.

Use cases

  • Check values copied from email, URLs, tokens, or configuration files.
  • Prepare deterministic test fixtures without a server-side dependency.
  • Inspect byte-level transformations before adding them to application code.

Tips for reliable output

  • Keep the original input beside the result while debugging.
  • Confirm the alphabet or MIME variant expected by the receiving system.
  • Use hexadecimal output when bytes are not valid text.
  • Test Unicode and empty-edge cases in your own integration.
  • Do not treat reversible encoding as a security control.

Processing details

Charset labels are normalized before TextDecoder is used. UTF-8, US-ASCII, and ISO-8859-1 are accepted.

Unsupported legacy charsets are rejected instead of being guessed.

Frequently asked questions

What input does the MIME Encoded Word Decoder accept?

MIME header value is accepted as plain text in the input area.

How does the MIME Encoded Word Decoder handle invalid data?

Unsupported legacy charsets are rejected instead of being guessed.

Is output from the MIME Encoded Word Decoder encrypted?

No. The transformation is an encoding or inspection operation, not encryption.

Can I use the MIME Encoded Word Decoder with Unicode text?

Yes. Text input is converted with UTF-8 where the format requires bytes.

What should I verify before using the result?

Adjacent encoded-words separated only by whitespace are joined as required for folded header text.

Format notes

PropertyValue
InputMIME header value
RunsLocally in the browser

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