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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds real value beyond that: it discloses that criteria are returned in 'original wording' and, critically, that 'Eligibility is confirmed only by the study team' — a caveat that prevents the agent from presenting registry criteria as an eligibility decision.

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?

A single long but front-loaded sentence that puts the verb, resource and identifier first, then enumerates returned fields. Nothing is wasted, though the field enumeration is dense and the sentence could be broken for readability.

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?

With an output schema present, the enumerated return fields are partly redundant, but the description still supplies the eligibility caveat and the 'original wording' nuance that structured fields cannot convey. Nothing needed to call the tool correctly is missing.

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 description coverage is 100%: nct_id is documented with an example and a regex pattern. The description's 'by its NCT number' merely restates the parameter's meaning without adding format or constraint detail beyond the schema, so the baseline 3 applies.

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 precise verb+resource+scope: 'Returns one clinical trial from ClinicalTrials.gov by its NCT number.' The singular 'one' plus the registry identifier cleanly separates it from the sibling find_clinical_trials search tool without even needing to name it.

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?

The need for an NCT number implies this is the lookup-by-ID path rather than a search path, but the description never explicitly says when to use it instead of find_clinical_trials, nor does it name that alternative. Usage is inferable but not stated.

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