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

With no annotations supplied, the description carries the full burden, and it does disclose a real behavioral trait beyond the schema: a cost of 1 credit per call, plus the extra payload (eligibility criteria, sites) returned in the detail mode. It says nothing about what happens with an unknown NCT id, whether results are paginated, or what a zero-filter call returns.

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 sentence with both modes front-loaded and the credit cost tucked in parentheses, so nothing is padded. The "or get one by NCT id" pivot is slightly telegraphic but does not obscure meaning.

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?

There is no output schema and no annotations, so the description must cover both purpose and behavior; it identifies both call shapes and the cost. The remaining gap is the all-optional parameter set — an agent cannot tell from this text whether a filterless call is a valid bulk listing or an error.

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 nominally 100%, but the per-parameter descriptions are type stubs ("string", "number 1-50"), so the schema conveys field names and little else. The description adds meaning only for nctId, leaving condition, intervention, location, status, and limit semantics to inference; the high coverage figure keeps this at the baseline 3.

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 a specific verb and resource ("Search clinical trials") and distinguishes two modes: a search and a single-record fetch by NCT id that returns eligibility criteria and sites. No sibling covers clinical trials, so the differentiation is implicit in the domain name rather than stated, which keeps it just short of a 5.

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 "or get one by NCT id" clause gives a clear conditional for choosing the detail mode over the search mode. It stops short of the highest bar because it never says when not to use this tool, nor whether a search requires at least one filter (all six parameters are optional).

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