Computer-executable instructions comprising some or all of a program can be delivered to a client for execution on a real-time basis such that the client receives anew the computer-executable instructions for each new execution of the program. Such an environment enables instrumentation instructions to be inserted into the computer-executable instructions after a request and prior to the delivery of the computer-executable instructions. The inserted instrumentation instructions can be spread across multiple deliveries of the same computer-executable instructions, and they can be modified to account for information received from previously inserted instrumentation instructions. The instrumentation instructions can be inserted as part of the server process, the client process, or as part of a proxy server that can be used at the discretion of the program developer.