Originally posted by eram:

you can repair tools from a workbench thats inside a building (has shelter)
the repair icon is next to the list of craftable items. and in early access repairing is free.

If it isnt free in full version, the game is going to be too grindy, considering tools break after few hits (specially axes and pickaxes). So having to waste even 1 Bar of bronze or iron is going to wreck the experience. Especially with multiple players on a server draining the ore supply.