What are your “hard rules” about commenting your code?

Question

I have seen the other questions but I am still not satisfied with the way this subject is covered.

I would like to extract a distiled list of things

Answer 1

There are no hard rules - hard rules lead to dogma and people generally follow dogma when they're not smart enough to think for themselves.

The guidelines I follow:

1/ Comments tell what is being done, code tells how it's being done - don't duplicate your effort.

2/ Comments should refer to blocks of code, not each line. That includes comments that explain whole files, whole functions or just a complicated snippet of code.

3/ If I think I'd come back in a year and not understand the code/comment combination then my comments aren't good enough yet.