This test attempts to:

  • examine whether the domain names of websites are blocked

  • detect the presence of “middle boxes” (software which could be used for censorship and/or traffic manipulation) in tested networks

  • assess which censorship circumvention techniques are capable of bypassing the censorship implemented by the “middle box”

HTTP is a protocol which transfers or exchanges data across the internet. It does so by handling a client’s request to connect to a server, and a server’s response to a client’s request. Every time you connect to a server, you (the client) send a request through the HTTP protocol to that server. Such requests include “HTTP headers”, some of which (the “Host header”) include information about the specific domain that you want to connect to. When you connect to, for example, the host header of your HTTP request includes information which communicates that you want to connect to that domain.

This test implements a series of techniques which help it evade getting detected from censors and then uses a list of domain names (such as to connect to an OONI backend control server, which sends the host headers of those domain names back to us. If a “middle box” is detected between the network path of the probe and the OONI backend control server, its fingerprint might be included in the JSON data that we receive from the backend control server. Such data also informs us if the tested domain names are blocked or not, as well as how the censor tried to fingerprint the censorship of those domains. This can sometimes lead to the identification of the type of infrastructure being used to implement censorship.

Note: The presence of a middle box is not necessarily indicative of censorship and/or traffic manipulation, as they are often used in networks for caching purposes.

Read the HTTP Host test specification.