Reconfigurable computing applications often need to divide computation between software running on a conventional desktop processor and hardware mapped to an FPGA. However, the reconfigurable computing development platforms available today either do not provide a sufficient mechanism for the communication and synchronization that is needed or else employ a complex & proprietary API specific to a given toolflow or device, limiting code portability. The Simple Interface for Reconfigurable Computing (SIRC) project provides a straightforward, portable and extensible open-source communication and synchronization API. It consists of both a software-side interface and a hardware-side interface that allows C++ code running on a host PC to communicate and synchronize with a Verilog-based circuit mapped to a FPGA. One key feature of this API is that both the hardware and software user interfaces can remain consistent across all platforms and future releases. This allows applications built for existing systems to migrate to different platforms without significant modification to user code.