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

Annotations already establish read-only, idempotent, open-world behavior, so the bar is lower; the description still adds useful context by inventorying exactly which fields come back and by explicitly excluding contact-person details, which prevents a wasted follow-up call. It does not cover error behavior for unknown or malformed ids.

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?

One front-loaded sentence: key scope first, the long field inventory and the negative disclosure last. It is dense but nothing is redundant with the schema or annotations, and the length is justified by the absent output schema.

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 no output schema, the returned-field enumeration and the contact-details exclusion do the heavy lifting, and the annotations carry the safety profile. Missing only failure semantics (unknown id, registry not covered) for full completeness.

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% so the baseline is 3, and the description goes further by enumerating id formats across registries (ChiCTR, CTRI, IRCT, DRKS, jRCT, NCT, ACTRN), which tells the agent it need not normalize or translate ids. The schema's own example covers only one of those formats, so this genuinely adds meaning.

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?

Names the exact resource (WHO Trial Registration Data Set for one trial) and its retrieval key (registry id from any covered registry), with concrete id examples spanning seven registries. An agent can instantly separate this single-record fetch from the sibling ictrp_search without opening a schema.

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 phrase 'by its registry id' implies you must already hold an identifier, which is the de facto when-to-use condition, but the description never states it as guidance, never says what to do without an id, and does not point to ictrp_search as the lookup alternative. Usage is inferable rather than stated.

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