The name of the code, SQPlab, stands for Sequential Quadratic Programming (SQP) laboratory. It is written in Matlab. This piece of software is used by the author as a kind of laboratory for trying techniques related to the SQP algorithm, but it has been designed so that it can be useful to many. It is also aimed at accompanying the hanging chain project developped along part III of the book 'Numerical Optimization – Theoretical and Practical Aspects' (second edition), by J.F. Bonnans, J.Ch. Gilbert, C. Lemaréchal, C. Sagastizábal, during which it is shown how to implement step by step many aspects of the algorithm.