The following is a non-exhaustive list of MIME Types detected by default in NiFi:

An example value for the Config Body property that will identify a file whose contents start with "abcd" as MIME Type "custom/abcd" and with extension ".abcd" would look like the following:

For a more complete list of Tika's default types (and additional details regarding customization of the value for the Config Body property), please refer to Apache Tika's documentation