We present a native-Julia nonlinear programming (NLP) solver MadNLP.jl. This solver implements the filter line-search interior-point method for constrained NLPs; to the best of our knowledge, MadNLP is currently the only native-Julia solver that is capable of handling general nonlinear equality/inequality-constrained optimization problems. MadNLP is interfaced with the algebraic modeling language JuMP.jl, the graph-based modeling language Plasmo.jl, and the NLP data structure NLPModels.jl.