What devices have you found useful when inspecting your stylii for cleanliness?

@rauliruegas I have been pulling my table and arm apart several times a day while I fashion and fit plinth inserts made from 28-mm thick MDF with constrained damping layers in between. On one occasion the small sliding weight got shifted accidentally and the cartridge was tracking close to the old Shure’s recommended 1.2 grams rather than the 2.1 grams it should be. Audibly there was something horribly wrong! Similar thing if too much fluff gets caught by the stylus. There are more nasties if the very fine nylon line holding the anti-skating weight comes off its pulley, or gets itself wrapped around the wire holding the pulley.

As far as I can tell, the tone arm itself is in very good condition, except for some minor corrosion on the electrical connectors to the cartridge. By design, the sliding balance weight is only good for 0 to 1.5 grams so I twist the main weight using a digital scale to get into the ballpark before final adjustment with the sliding weight. There has been a lot of trial, and a lot of error! The classic error was using a small cable tie to fasten the motor cable to the transit mounting, which is spring loaded and well clear of the motor when the whole thing is upside down. Once the right way up, and hidden inside the plinth, the motor descended and got fouled by the cable tie!

The record that I mainly test with is an Accoustic Research demonstration disk, and I use a jazz track with trumpet, piano, bass and drums. An alternative is an Original Master Recording of Sir Adrian Boult conducting Elgar’s orchestral transcription of a Bach organ piece. Plenty of braying brass there! I have a couple of test disks - the "Ultimate Analogue Test LP" and a German equivalent. More vinyl is on its way including Hyperion’s Shostakovich Piano Concertos, which I already use as tests on SACD.

I really am having fun, and learning lots ...

Dear @rauliruegas . I hear you on the suspension issue with too much cleaning. That's why I included my Decca cartridges note. As you know, they don't have a cantilever as such and can take a beating more than a potentially sensitive moving coil. Nevertheless, I felt it statistically relevant to point out there is at least one of us cleaning per side. My records are clean, and it's more of a preventative habit than anything else. 

@richardbrand I inspect styluses with a loupe with a built-in LED light. I also use a digital otoscope with a probe if a screen view is needed.

....trained ants....It's all about scale....

It is interesting to read the diversity of routines that everyone has developed to address this simple task.  I have three main TTs, two with fixed (i.e. non removable headshells) and one with a removable headshell feature.  In all cases I check the stylii for wear using a Wild-Herrbrugg microscope.  In the case of the non-removable headshell arms the cartridges must be removed for inspection.  In all cases the microscope inspection is performed bi-annually, so it is not too burdensome.  For every day cleaning I do many things: in all cases before every play of every side I very lightly apply Stylast to the tip of the diamond only.  The record itself is brushed.  After each side is played the stylus is inspected and if there is any debris collected it is removed.  I have a soft brush provided by Audio Technica, I have a stiff brush provided by Ortofon, I have the gel thingy from Ozow or whoever, and I have an ultrasonic brush that when used with a drop of distilled water does the best job of all.  I bought it from Amazon for not much money.  BTW, I used the microscope to evaluate all these brushes and such plus blue tack.  The ultrasonic brush, made by Hudson if memory serves, did the best job by far.