Where do I find the boundary string?

It is declared in the top-level Content-Type header as boundary="...". The actual separators in the body are prefixed with two dashes (--boundary), and the final separator is followed by two dashes.

Why are some parts empty?

Multipart/form-data often includes empty parts for unset form fields, or a leading/trailing empty segment from the boundary split. Filter parts with empty bodies after parsing.

TASK

Parse a multipart MIME message and extract each part

Break a multipart/form-data or multipart/mixed MIME message into its constituent headers and bodies for inspection or reprocessing.

1

Multipart MIME bundles several parts (text, attachments, form fields) separated by a boundary string. Each part has its own headers and body. Parsing requires splitting on the boundary and decoding each part's Content-Transfer-Encoding.
2

MIME Decoder →
Paste the full multipart message. The tool splits on the boundary, extracts each part's headers and body, and applies the transfer encoding (base64, quoted-printable, 7bit).
3

MIME Types Reference →
Look up the Content-Type of each extracted part to understand how to render or save it (e.g. image/jpeg → save as binary, text/plain → display).
4

Base64 Decoder →
If a part's body is still Base64 after MIME decode (nested encoding), decode it here to recover the original bytes.

Frequently asked questions

Where do I find the boundary string?: It is declared in the top-level Content-Type header as boundary="...". The actual separators in the body are prefixed with two dashes (--boundary), and the final separator is followed by two dashes.
Why are some parts empty?: Multipart/form-data often includes empty parts for unset form fields, or a leading/trailing empty segment from the boundary split. Filter parts with empty bodies after parsing.