Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint and destructiveHint annotations, the description discloses important behavior: results are newest-first, items are thin references rather than full runs, automatic fires are stored as diagnoses, outputs are sampled/truncated, and large trace values are shortened. This is exactly the kind of behavioral context an agent needs to interpret results correctly.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.