Different board houses require different design specs. There are many features to choose from, so these specs are packaged in a single file called a DRU.

OSH Park

OSH wants you to follow these instructions, which will embed both the OSH DRU and some automated job submission features in Eagle. After install, my button displays a broken image link, but otherwise seems to work fine.

Seeed

I haven’t been able to find any DRUs on the Seeed site that are newer than this, so that’s what I’ll go with.

Eagle

Once you’ve completed the rough draft of your design, type DRU and hit Enter. Next, you’ll click Load, then navigate to the corresponding DRU. On my Mac these are found in Documents/Eagle/design rules. Pick the DRU you want, then click Check. If things go well, you’ll get no errors. Note that you may get warnings, which may or may not be a deal breaker. I have tons of mini stubs in my autorouting, perhaps flagged for being too short, but this do not appear to impact fabrication.

Once you’re satisfied with the DRU, go to File > CAM Processor. Both OSH and Seeed have export templates found under Load Job File > Third Party. Each will push out a .zip for you to upload to the corresponding service.