We present SUSPECT, an open source toolkit that symbolically analyzesmixed-integer nonlinear optimization problems formulated using the Python alge-braic modeling library Pyomo. We present the data structures and algorithms used toimplement SUSPECT. SUSPECT works on a directed acyclic graph representation ofthe optimization problem to perform: bounds tightening, bound propagation, mono-tonicity detection, and convexity detection. We show how the tree-walking rules inSUSPECT balance the need for lightweight computation with effective special struc-ture detection. SUSPECT can be used as a standalone tool or as a Python library to beintegrated in other tools or solvers. We highlight the easy extensibility of SUSPECTwith several recent convexity detection tricks from the literature. We also report ex-perimental results on the MINLPLib 2 dataset.