You gain Crafting ranks every level equal to half (rounded up) of your Proficiency Bonus, and you may have a maximum rank of twice your Character Level in any discipline (up to rank 20).
You may also gain one tenth of a rank for each unique item you craft. A unique item meaning an item or effect (in regards to Runesmithing and Provisioning) with unique properties. A rank 1 Dagger has different properties to a rank 2 Dagger, so they each count individually.
Once you have gained a full rank in this manner, you are incapable of gaining more partial ranks until you have passed a 'Certification Test'. This test involves successfully crafting an item one rank higher than your new rank. Ranks gained through level up are assumed you have completed this test.
There are 6 custom crafting disciplines in Sarsei, which should cover all things players may wish to craft:
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