  When learning to use an Application Programming Interface (API), programmers
need to understand the inputs and outputs (I/O) of the API functions. Current
documentation tools automatically document the static information of I/O, such
as parameter types and names. What is missing from these tools is dynamic
information, such as I/O examples---actual valid values of inputs that produce
certain outputs. In this paper, we demonstrate a prototype toolset we built to
generate I/O examples. Our tool logs I/O values when API functions are
executed, for example in running test suites. Then, the tool puts I/O values
into API documents as I/O examples. Our tool has three programs: 1) funcWatch,
which collects I/O values when API developers run test suites, 2) ioSelect,
which selects one I/O example from a set of I/O values, and 3) ioPresent, which
embeds the I/O examples into documents. In a preliminary evaluation, we used
our tool to generate four hundred I/O examples for three C libraries: ffmpeg,
libssh, and protobuf-c.
