MIME Decoder
Decode MIME encoded text including Base64, Quoted-Printable, and MIME headers with auto-detection.
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Decode MIME Text
Decoded Result
Manual Mode
What is MIME Encoding?
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.
How to Use This MIME Decoder
- Paste MIME encoded text into the input area on the left panel.
- Click Auto Decode to let the tool detect and decode the encoding type automatically.
- Use the Manual Mode buttons (Base64, Quoted-Printable, MIME Header) to force a specific decoder.
- The Detected Encoding section shows what encoding was identified in your input.
- Click Copy Result to copy the decoded text to your clipboard.
Common Use Cases
- 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.
Frequently Asked Questions
What is the difference between Base64 and Quoted-Printable?
Base64 encodes data into a compact ASCII representation using 64 characters, making it ideal for binary data and attachments. Quoted-Printable preserves most ASCII characters as-is and only encodes non-printable bytes (using =XX), making it more human-readable for text content with occasional special characters.
What is MIME Header Encoding (RFC 2047)?
MIME Header Encoding allows non-ASCII characters in email headers. The format is =?charset?encoding?encoded_text?= where charset is the character set (e.g., UTF-8), encoding is either B (Base64) or Q (Quoted-Printable variant), and encoded_text is the encoded content.
Can I decode email attachments with this tool?
This tool decodes MIME-encoded text content. For binary attachments (images, PDFs, etc.), the Base64 decode output will show the raw binary bytes. Use a dedicated Base64 to file converter for reconstructing attachment files.
How does auto-detection work?
The auto-detection checks your input against known MIME encoding patterns: MIME Header encoding (=?...?=), Base64 (valid Base64 string), and Quoted-Printable (=XX pairs). If multiple patterns match, it prioritizes MIME Header > Base64 > Quoted-Printable.
Is this tool safe for sensitive data?
Yes. All decoding happens entirely in your browser using JavaScript. No data is sent to any server. Your encoded content never leaves your device.
