We now offer an official Cleverbot API at www.cleverbot.com/api. All end users must sign up for an API key, which is currently free for low usage numbers.
There are many unofficial Cleverbot APIs made available by others. Cleverbot requires high-powered servers to process user input and return a reply. The revenue to pay for these servers comes almost wholly from ads shown to users while chatting. Unofficial APIs cost us money. They go against our terms of usage, and we ask developers not to use or implement them.
Unofficial APIs may stop working without warning, and often do not correctly implement the context that real Cleverbot replies rely upon.
Note that prior to our official Cleverbot API, we asked all unofficial APIs to add a botapi parameter to all requests to identify their APIs. For example &botapi=[YOUR_API_NAME]. This allowed us to measure usage of unofficial APIs.