Libfastcounters is a C library to maintain counters. It makes it convenient for a server program to count many kinds of events. Incrementing is fast, on the order of nanoseconds. Incrementing is atomic. Counters are shared across processes. Counters are persistent. You can address counters by number or by name. Libfastcounters includes a command line tool to create, modify, and read the persistent counters file.