Photonic integrated circuits play a pivotal role in many applications. Particularly powerful are circuits based on meshes of reconfigurable Mach–Zehnder interferometers as they enable active processing of light. This meets demands accross different fields, from communication to signal and information processing and sensor applications. Here, we use a reconfigurable photonic integrated circuit to realize a spatially resolving detector of amplitudes and phases of an electromagnetic field distribution. This is achieved by optically sampling free-space beams with a carefully designed input interface and subsequently processing the resulting on-chip light within the photonic mesh of interferometers. To perform measurements of this kind, we develop and experimentally implement a versatile method for the calibration and operation of such integrated photonics based detectors. Our technique works in a wide parameter range, even when running the chip off the design wavelength. Amplitude, phase, and polarization sensitive measurements are of enormous importance in modern science and technology, providing a vast range of applications for such integrated detectors.