Magnet links

The Magnet URI scheme, defines the format of magnet links, a de facto standard for identifying files by their content, via cryptographic hash value rather than by their location.

Although magnet links can be used in a number of contexts, they are particularly useful in peer-to-peer file sharing networks because they allow resources to be referred to without the need for a continuously available host, and can be generated by anyone who already has the file, without the need for a central authority to issue them. This makes them popular for use as "guaranteed" search terms within the file sharing community where anyone can distribute a magnet link to ensure that the resource retrieved by that link is the one intended, regardless of how it is retrieved.

The standard for Magnet URIs was developed by Bitzi in 2002, partly as a "vendor- and project-neutral generalization" of the ed2k: and freenet: URI schemes used by eDonkey2000 and Freenet, respectively, and attempts to follow official IETF URI standards as closely as possible.

Magnet URIs consist of a series of one or more parameters, the order of which is not significant, formatted in the same way as query strings that ordinarily terminate HTTP URLs. The most common parameter is "xt" ("exact topic"), which is generally a URN formed from the content hash of a particular file, e.g.:

magnet:?xt=urn:btih:c12fe1c06bba254a9dc9f519b335aa7c1367a88a&dn

This refers to the hex-encoded SHA-1 hash of the torrent file info section in question. Note that, although a particular file is indicated, an availability search for it must still be carried out by the client application.

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