We prove that a parametric Lipschitz surface of codimension 1 in a smooth manifold induces a boundary in the sense of currents (roughly speaking, surrounds a "domain" with an eventual multiplicity and together with it forms a pair for the Stokes theorem) if and only if it passes a test in terms of crossing the surface by "almost all" curves. We use the AM-modulus recently introduced in [22] to measure the exceptional family of curves.