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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-obvious behavior: the tool is metered at $0.005 USDC per call via x402, which matters for agent budgeting decisions. It omits rate limits and pagination behavior, keeping it short of a 5.

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?

Three tight sentences: purpose and source first, filterable dimensions second, cost last. Every clause carries information and nothing is padded.

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 description usefully enumerates returned fields (status, phase, sponsor, interventions, enrollment, links), which is exactly the compensation needed. Remaining gap is the undocumented 'limit' parameter and pagination behavior.

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 only 25% (only 'status' has a description), so the description must compensate. It does clarify the required 'q' (condition, drug or keyword) and confirms status/location filtering, but says nothing about 'limit' or result-cap semantics, leaving one of four parameters undocumented in both places.

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 ('Clinical trials search') plus the data source (ClinicalTrials.gov) and the queryable domain (condition, drug, keyword). An agent can immediately tell this is a trial-registry lookup rather than a generic web search or the sibling 'drug' tool.

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?

It hints at usage ('Filter by status and location') and names the upstream source, but never states when to prefer this over alternatives such as 'drug', 'papers', or 'research', nor any when-not condition. Usage is implied rather than prescribed.

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