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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is well covered. The description adds that the data is 'published' and 'Sourced from the EU Clinical Trials Information System,' plus a detailed return-value list, but it does not disclose additional operational behavior such as freshness, rate limits, or error cases. No contradiction with annotations exists.

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 front-loads the purpose and example identifier, then lists the extensive expected contents. The list is long but justified because there is no output schema to communicate the return shape. It is wordy but not padded with irrelevant information.

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?

This is a single-parameter lookup with no output schema, and the description fully specifies the required identifier, gives an example, names the source, and enumerates the returned fields. Nothing needed to select and invoke the tool 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 description coverage is 100%: the ct_number property already includes a type and an example. The description merely repeats the same example and meaning without adding materially new semantics. Baseline 3 is appropriate because the schema already carries the full parameter documentation.

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 exactly what the tool does: 'Full published record for one EU clinical trial by its CTIS number,' with an example identifier. It enumerates the specific fields returned, making the resource unambiguous. The singular 'one... by its CTIS number' clearly distinguishes it from search and recent-list siblings.

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 trigger condition is clear: use this when you have a CTIS number and need the full published trial record. It does not explicitly name alternatives like ctis_search_trials or ctis_recent_authorisations, nor does it state when not to use it, so it falls short of a 5. The context is still clear enough for an agent to make the right choice.

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