  Blazars research is one of the hot topics of contemporary extra-galactic
astrophysics. That is because these sources are the most abundant type of
extra-galactic gamma-ray sources and are suspected to play a central role in
multi-messenger astrophysics. We have used swift_xrtproc, a tool to carry out
an accurate spectral and photometric analysis of the Swift-XRT data of all
blazars observed by Swift at least 50 times between December 2004 and the end
of 2020. We present a database of X-ray spectra, best-fit parameter values,
count-rates and flux estimations in several energy bands of over 31,000 X-ray
observations and single snapshots of 65 blazars. The results of the X-ray
analysis have been combined with other multi-frequency archival data to
assemble the broad-band Spectral Energy Distributions (SEDs) and the long-term
light-curves of all sources in the sample. Our study shows that large X-ray
luminosity variability on different timescales is present in all objects.
Spectral changes are also frequently observed with a "harder-when-brighter" or
"softer-when-brighter" behavior depending on the SED type of the blazars. The
peak energy of the synchrotron component nu_peak in the SED of HBL blazars,
estimated from the log-parabolic shape of their X-ray spectra, also exhibits
very large changes in the same source, spanning a range of over two orders of
magnitude in Mrk421 and Mrk501, the objects with the best data sets in our
sample.
