Learn English – it should work vs it must work

meaning

I want to inquire about the difference in meaning between these two sentences:

The code must work perfectly.
The code should work perfectly.

For instance how the usage of "must" and "should" in the previous sentences will change the meaning?

English modals have a lot of shades of meanings, but to keep it simple, for this specific situation:

Should X expresses unconfirmed belief that X happened or will happen. It is synonymous with is expected to X:

The code should work perfectly (but we won't know for sure until we try it.)

Must X expresses that something cannot happen unless X happened or definitely will happen. It is synonymous with is required to X or has to X.

The code must work perfectly (or our job isn't complete, etc.)

Should X can be used as a polite or gentler must X.