eCAP is a software interface that allows a network application, such as an HTTP proxy or an ICAP server, to outsource content analysis and adaptation to a loadable module. For each applicable protocol message being processed, an eCAP-enabled host application supplies the message details to the adaptation module and gets back an adapted message, a "not interested" response, or a "block this message now!" instruction. These exchanges often include message bodies.

The libecap library implements eCAP API in C++.