De or het modelcode?

The correct Dutch article is:

de modelcode

Rule Words ending in -ode: always de. See the rule

How to use modelcode

the modelcodede modelcode
this modelcodedeze modelcode
that modelcodedie modelcode
our modelcodeonze modelcode
your modelcodejouw modelcode
every modelcodeelke modelcode
which modelcode?welke modelcode?
a big modelcode / the big modelcodeeen grote modelcode, de grote modelcode