On-shell methods have been shown to be a powerful tool to compute higher-point and loop amplitudes. However, most of the time we hear about the applications for renormalizable theories. In this talk, I will give an introduction to spinors and to (massless/massive) amplitudes and show that we can indeed apply these methods for general effective field theories. Afterwards, I am going to discuss how these methods make it easier to build a dark matter model with a massive particle with general spin and work out the phenomenology.
