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In this paper we present the WeCAPP variable star catalogue towards the bulgeof M31. The observations of the WeCAPP microlensing survey (optical R and Ibands) during three years (2000-2003) result in a database with unprecedentedtime coverage for an extragalactic variable star study. We detect 23781variable sources in a 16.1' x 16.6' field centered on the nucleus of M31. Thecatalogue of variable stars contains the positions, the periods and thevariations in the R and I bands. We classify the variables according to theirposition in the R-band period-amplitude plane. Three groups can bedistinguished; while the first two groups can be mainly associated withCepheid-like variables (population I Cepheids in group I, type II Cepheids andRV Tauri stars in group II), the third one consists of Long Period Variables(LPVs). We detect 37 RV Tauri stars and 11 RV Tauri candidates which is one ofthe largest collections of this class of stars to date. The classificationscheme is supported by Fourier decomposition of the light curves. Our datashows a correlation of the low-order Fourier coefficients Phi_21 with Phi_31for classical Cepheids, as well for type II Cepheids and RV Tauri stars.Correlating our sample of variable stars with the X-ray based catalogues ofKaaret (2002) and Kong et al. (2002) results in 23 and 31 coincidences, 8 ofwhich are M31 globular clusters. The number density of detected variables isclearly not symmetric, which has to be included in the calculations of theexpected microlensing event rate towards M31. This asymmetry is due to theenhanced extinction in the spiral arms superimposed on the bulge of M31 whichreduces the number of sources to about 60%, if compared to areas of equivalentbulge brightness (without enhanced extinction being present).Comment: 22 pages, re-submitted to A&A after referee comments have been taken  into accoun

The Wendelstein Calar Alto Pixellensing Project (WeCAPP): the M 31 variable star catalogue