GreyCat C API and GCL Standard Library reference. Use for: (1) Native C development with gc_machine_t context, tensors, objects, memory management, HTTP, crypto, I/O; (2) GCL Standard Library modules - std::core (Date/Time/Tuple/geospatial types), std::runtime (Scheduler/Task/Logger/User/Security/System/OpenAPI/MCP), std::io (CSV/JSON/XML/HTTP/Email/FileWalker), std::util (Queue/Stack/SlidingWindow/Gaussian/Histogram/Quantizers/Random/Plot). Keywords: GreyCat, GCL, native functions, tensors, task automation, scheduler.