MIME Decoder

MIME (Multipurpose Internet Mail Extensions) encoding is used to convert binary or non-ASCII data into a format that can be safely transmitted over text-based protocols like email (SMTP). MIME defines several Content-Transfer-Encoding schemes to handle different types of data.

This tool decodes three common MIME encoding formats: Base64, Quoted-Printable, and MIME Header Encoding (using the B and Q schemes defined in RFC 2047).

Supported Encoding Types

• Base64 — Encodes binary data into ASCII using a 64-character alphabet. Used for email attachments and binary content.
• Quoted-Printable (QP) — Encodes text with mostly ASCII characters using =XX notation for non-printable bytes. Used for text content with special characters.
• MIME Header (RFC 2047) — Encodes non-ASCII text in email headers (Subject, From, To) using =?charset?B?... (Base64) or =?charset?Q?... (Quoted-Printable) format.

1. Paste MIME encoded text into the input area on the left panel.
2. Click Auto Decode to let the tool detect and decode the encoding type automatically.
3. Use the Manual Mode buttons (Base64, Quoted-Printable, MIME Header) to force a specific decoder.
4. The Detected Encoding section shows what encoding was identified in your input.
5. Click Copy Result to copy the decoded text to your clipboard.

• Email troubleshooting — Decode email source (raw MIME) to read encoded message bodies and attachments.
• Email header analysis — Decode MIME-encoded Subject, From, and To headers in internationalized emails.
• Data inspection — Quickly decode Base64 or Quoted-Printable encoded data without external tools.
• Web development — Debug MIME encoding in form submissions, API payloads, and email generation libraries.
• Security analysis — Inspect MIME-encoded payloads in email headers and message sources for security research.