Position: Agent Should Invoke External Tools ONLY When Epistemically Necessary

ArXi:2506.00886v3 Announce Type: replace As large language models evolve into tool-augmented agents, a central question remains unresolved: when is external tool use actually justified? Existing agent frameworks typically treat tools as ordinary actions and optimize for task success or reward, offering little principled distinction between epistemically necessary interaction and unnecessary delegation. This position paper argues that agents should invoke external tools only when epistemically necessary.