  The parity of the number of elementary excitations present in a quantum
system provides important insights into its physical properties. Parity
measurements are used, for example, to tomographically reconstruct quantum
states or to determine if a decay of an excitation has occurred, information
which can be used for quantum error correction in computation or communication
protocols. Here we demonstrate a versatile parity detector for propagating
microwaves, which distinguishes between radiation fields containing an even or
odd number n of photons, both in a single-shot measurement and without
perturbing the parity of the detected field. We showcase applications of the
detector for direct Wigner tomography of propagating microwaves and heralded
generation of Schr\"odinger cat states. This parity detection scheme is
applicable over a broad frequency range and may prove useful, for example, for
heralded or fault-tolerant quantum communication protocols.
