Polarization, the vector nature of electromagnetic waves, plays a vital role in optics. Polarization is characterized by the amplitude contrast and phase difference between two orthogonal polarization states. The present polarimeters usually perform a series of intensity measurements to carry out the polarization detection, making the process bulky and time-consuming. Thereby, compact and broadband-available polarimetry within a single snapshot is urgently demanded. We propose an all-liquid-crystal polarimeter for broadband polarization detection. It is cascaded by a q-plate and a polarization grating. The former is electrically tuned to meet the half-wave condition, whereas the latter is driven to deviate from this condition. After a polarized light passes through this device followed by a polarizer, its amplitude contrast and phase difference between orthogonal spins are read directly from the diffraction pattern. The intensity contrast between ±1st orders depicts the amplitude contrast, whereas the rotating angle of the dark split reveals the phase difference. The Stokes parameters can be calculated accordingly. The polarimeter works in a broad spectral range of 470 to 1100 nm. Through presetting a q-plate array, polarization imaging is demonstrated. It supplies an all-liquid-crystal and full-visible-band tunable Stokes polarimeter that significantly promotes advances in polarization optics.