Flat shell for an accelerator card

Using a flat shell for an accelerator card includes reading a flat shell from one or more computer readable storage media using computer hardware, wherein the flat shell is a synthesized, unplaced, and unrouted top-level circuit design specifying platform circuitry. A kernel specifying user circuitry is synthesized using the computer hardware. The kernel is obtained from the one or more computer readable storage media. The synthesized kernel is linked, using the computer hardware, to the flat shell forming a unified circuit design. The unified circuit design is placed and routed, using the computer hardware, to generate a placed and routed circuit design specifying the platform circuitry and the user circuitry for implementation in an integrated circuit.