Diamond polycrystalline films have been synthesised using the chemical vapour deposition technique in order to fabricate new types of photodetectors for the characterisation of X-ray light sources as encountered in synchrotron experiments. We present here new diamond-based devices for three different applications, including (i) semitransparent beam position monitors with high position resolution (<2μm), (ii) beam profile monitors with 20μ pitch resolution, and (iii) ultrafast diamond detectors for the 100ps range that enable the intensity and temporal monitoring of fast X-ray pulses. These devices can be used for in-line characterisation of synchrotron beam line experiments as well as for synchrotron machine diagnostics.