Monitoring 100 Gbps network links is a challenging task. Packet filtering allows monitoring applications to focus on the relevant data, discarding packets that do not provide any valuable information. However, such a large line rate calls for custom hardware solutions. This work presents a tool for automatically synthesizing packets filters from a custom grammar, which defines filters in a human-readable format. Thanks to parser generators (Bison) and lexical analyzers (Flex), Verilog code is automatically generated from the filter specification. Rules can be applied over a protocol, a protocol field, the packet payload, or a combination of them. The generated filters use standard AXI4-Stream interfaces, which seamlessly integrate in the packet filtering framework that we have developed for the integrated block for 100G Ethernet available in Xilinx Ultrascale devices. We present the results for two proof-of-concept packet filtering designs. Furthermore, filters are fully pipelined, so the full 100 Gb/s rate is guaranteed. As the framework uses a cut-through approach, latency is kept to a minimum. Finally, the proposed framework allows for the integration of more complex payload-level filters, written in C language with the Vivado-HLS tool.