Devices relying on microwave circuitry form a cornerstone of many classical and emerging quantum technologies. A capability to provide in-situ, noninvasive, and direct imaging of the microwave fields above such devices would be a powerful tool for their function and failure analysis. In this work, we build on recent achievements in magnetometry using ensembles of nitrogen-vacancy centers in diamond, to present a widefield microwave microscope with few-micron resolution over a millimeter-scale field of view, 130nTHz−1/2 microwave-amplitude sensitivity, a dynamic range of 48 dB, and submillisecond temporal resolution. We use our microscope to image the microwave field a few microns above a range of microwave circuitry components, and to characterize an alternative atom-chip design. Our results open the way to high-throughput characterization and debugging of complex multicomponent microwave devices, including real-time exploration of device operation.