The Design Rule Check is part of the PDK. Both the Magic and OpenLane tools make use of it.
It contains rules that check things like:
- The gate of the MOSFET are the correct dimensions,
- Wires on the metal layers are not too narrow and not too close,
- Check that MOSFET gates are protected if they have long connecting wires - this is called an antenna rule.
There are a few thousand rules in the Skywater130 PDK DRC. As the process/node gets smaller, the number of rules increases.
You can find out more about the DRC checks performed by OpenLANE in Mohamed Shalan’s OpenLane FOSSI dialup presentation
I hadn't done any verification before and it was a kind of light bulb moment of what it could bring to your confidence in a particular digital design.