Cold stellar streams, remnants of tidally disrupted globular clusters, have been employed as exquisite tracers of dark matter in the Milky Way. Because of their different positions in phase space, different ages, and different levels of observational scrutiny, different streams tell us different things about the Galaxy. We employ a Cramer–Rao or Fisher-matrix approach to understand the quantitative information content in the known streams. In simple, static, analytic models of the Milky Way, streams on eccentric orbits contain the most information about the dark-matter shape. For any individual stream, there are near-degeneracies between dark-matter halo properties and parameters describing the Galactic bulge, disk and the stream progenitor itself, but we find that simultaneous fitting of multiple streams ought to constrain all parameters to a precision of a few percent. At this level, simulated dark matter halos deviate from analytic parametrizations, so we chart the way forward by discussing constraints streams place on more flexible models of the Galactic gravitational potential.