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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered. The description adds real behavioral context beyond that: the complete set of returned fields and the explicit exclusion 'Contact-person details are not returned.' It doesn't say what happens on an unknown/malformed ACTRN, which keeps 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?

Front-loaded with the core action, then return fields, then the exclusion, then the alternative route — a sensible order. The long field enumeration is a run-on sentence, but with no output schema each item sets real expectations, so it earns most of its length.

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 single-parameter read tool with no output schema, the description covers payload contents, the one notable omission (contact details), and how to obtain an ACTRN. Nothing an agent needs in order to call it 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 coverage is 100% and the parameter description already covers the optional 'ACTRN' prefix and the 14-digit form; the description's example merely repeats it. Baseline 3 applies since the schema does the heavy lifting and the description adds no new syntax or validation semantics.

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+resource+scope: 'Full ANZCTR record for one trial by its ACTRN', then enumerates exactly which fields come back. It is clearly distinguishable from discovery-style siblings because it says the input is a single known ACTRN, not a query.

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?

Explicitly routes the agent: 'To FIND ANZCTR trials by keyword, condition or intervention, use ictrp_search with registry "ANZCTR" ... then pass a returned ACTRN here.' This names the alternative, the condition that selects it, and the hand-off sequence.

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