Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new context: the response includes the full change history and citing papers, and the answer should surface WHO ICTRP attribution plus the WHO processing date — a provenance constraint the annotations cannot express.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the usage trigger and then the return content, with no filler. The second sentence is dense and slightly clipped ('Show a WHO ICTRP record with its attribution') but every clause carries real instruction.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter lookup with no output schema, the description covers trigger, scope, returned content and provenance/attribution handling. The only remaining gap is failure behavior — an unknown or malformed registry number — which the description does not address.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the nct_id field already carries a pattern and examples, so the baseline is 3. The description goes beyond it by naming the accepted identifier namespaces (NCT, ISRCTN, ChiCTR, CTRI, CTIS 'and others'), which tells the agent the parameter is not NCT-only despite the field being named nct_id.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('get a clinical trial') and narrows the scope to exactly one trial looked up by registry number, which cleanly separates it from list_trials. It also enumerates the payload ('design, outcomes and dates, every change recorded and the papers that cite it'), so the agent knows the shape of the result before calling.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

'Use this when the user asks about one clinical trial by its registry number' gives an explicit trigger condition and an implicit alternative (list_trials for browsing). It stops short of naming that sibling or stating what to do when the user only has a title or sponsor rather than an identifier.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.