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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive hints. The description adds valuable behavioral detail beyond those hints: it splits results by trial status, lists sponsors and member states, and specifies newest-authorisation-first ordering, giving the agent a clear picture of the response shape without an output schema.

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?

The description is three sentences with no filler. It front-loads the core scope and resource, then adds the distinguishing behavioral details (status split, sponsors, member states) and concludes with a concrete user question the tool answers.

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?

Given the read-only, idempotent annotations and complete parameter schema, the description covers what the agent needs to know: what data is returned, how it is organized, and what question it answers. Without an output schema, the description still adequately describes the response composition (statuses, sponsors, member states) and ordering.

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%, so the schema fully documents all four parameters. The description adds some semantic context by noting that results cover every EU/EEA trial for a medicine and that status splits are included, which loosely relates to recruiting_only, but it does not substantially extend the meaning beyond what the input schema already provides.

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?

The description states a specific verb and resource: it returns EU/EEA clinical trials for a named medicine from the EU Clinical Trials Information System, ordered newest authorisation first. It clearly differentiates itself from siblings like ctis_recent_authorisations and ctis_search_trials by focusing on drug-specific trial enumeration with status breakdowns.

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 description explicitly frames when to use it: answering 'what is running in Europe for this drug'. It provides clear context for drug-specific queries but does not explicitly mention when not to use it or name alternative sibling tools, so it stops short of full routing guidance.

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