The Repair Tool functions as a hybrid of a Scanner and a portable Fabricator, used to repair damaged vehicles and bases. Its blueprint is not available by default — it must be unlocked via scans found in the world, so finding it is itself a small exploration objective.
It becomes essential once you rely on the Tadpole and forward bases, where Twin Sitarays and Bulletheads routinely damage hulls and structures far from a Fabricator.