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.
If you choose one of your Crafting skills as your Expertise, add double your Crafting rank when rolling the check.
There are 6 custom crafting disciplines in Sarsei, which should cover all things players may wish to craft:
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