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

Annotations already declare readOnly/idempotent/non-destructive and closed-world, so the safety profile is covered. The description adds substantive context beyond that: results come from a curated index and are summary-level, requiring a follow-up get_paper call for the full record, and each hit carries a registry identifier. It stops short of stating result ordering or pagination behavior, so it is not 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?

Two short sentences, front-loaded with the scope statement and followed immediately by the actionable handoff. No filler or restatement of the tool name.

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 a full output schema and 100% parameter coverage, the description only needs to establish scope and the follow-up path, both of which it does. Minor gap: it does not explain how registry choice affects result content or overlap between the two sources, which matters for a multi-registry search.

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 every parameter (query, limit, offset, year_from/year_to, registry) is already documented with bounds and defaults. The description only echoes the registry sources that the enum already declares, adding no syntax or query-construction guidance beyond the schema. Baseline 3 is appropriate.

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 ("Search clinical trial registrations") and names the two covered registries (ClinicalTrials.gov, WHO ICTRP) plus the index scope. That is clearly distinguishable from siblings like search_papers or search_authors without opening any schema.

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?

Gives an explicit downstream routing rule: each result carries a registry id, and get_paper should be used with it for the full record. It does not contrast itself against search_papers for mixed literature/trial queries, so there is no explicit when-not guidance, but the usage context is clear.

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