AFF3CT is an open source toolbox dedicated to Forward Error Correction (FEC or channel coding). Itsupports a broad range of codes: from widespread turbo codes and Low-Density Parity-Check (LDPC)codestomorerecentpolarcodes.ThetoolboxiswritteninC++andcanbeusedeitherasasimulatortoquickly evaluate algorithms characteristics, or as a library in Software Defined Radio (SDR) systems orfor other specific needs. Most of the decoding algorithm implementations aim at low latency and highthroughput, targeting multiple Gb/s on modern CPUs. This is crucial in both simulation and SDR usecases:MonteCarlosimulationsrequirehighperformanceimplementationastheycommonlytargettheestimation of approximately 1012bits. On the other hand, the implementations in real systems haveto be very efficient to be competitive against dedicated hardware ones. Finally, AFF3CT emphasizesthe reproducibility of state-of-the-art results by providing public references and open, modular sourcecode.