# Payload Extensions

Payload extensions add a custom checkbox to the payload build menu via the [register\_payload\_extension](/crystalc2/documentation/sleep/functions.md#register_payload_extension) sleep function.  They are useful for merging evasion or other runtime capabilities into the agent, where you want the easy option of enabling/disabling them each time you build a new payload.  Capabilities that you always want merged are better off being put in the `agent.spec` file directly.

Your spec file must use the `ext` label, e.g. `ext.64` and/or `ext.x86`.  See the SOCKS extension as an example.

{% embed url="<https://github.com/crystal-c2/crystal-extensions/tree/master/socks>" %}


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