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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable operational context beyond annotations: source attribution (Orphadata/Orphanet), licensing (CC BY 4.0), and access characteristics ('no auth, unlimited free'). It does not discuss error behavior or missing-code responses, but for a read-only lookup the disclosures are sufficient.

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 compact and front-loaded: it states the action and resource in the first clause, then lists return fields, then supplies source/licensing. Every sentence contributes information, with no repetition of schema content or filler.

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 an output schema present, return-value explanation is not required, yet the description still summarizes the key output fields. It includes the required parameter, the optional language parameter's default is covered by the schema, and annotations provide the safety profile. The only minor omission is explicit sibling routing, but that is a usage-guidelines nuance rather than a completeness gap.

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 already fully documents both parameters (orphacode and lang, including the enum values). The description reinforces that the tool looks up by ORPHAcode but adds no new syntax, formatting, or behavioral detail beyond what the schema provides. Baseline 3 is appropriate when the schema carries the semantic load.

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 opens with a specific verb and resource: 'Get prevalence and incidence data for a rare disease by its Orphanet ORPHAcode.' It enumerates the exact return fields (geographic area, measurement type, prevalence class, numeric mean, PMID citations), which makes the tool's scope unambiguous and clearly distinct from orphan data siblings like disease_lookup or disease_phenotypes without needing to name them.

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 implies when to use the tool: when you have an ORPHAcode and need epidemiology data. It does not explicitly compare against sibling tools or state when-not-to-use, but the context is clear enough that an agent can infer the appropriate selection. Lacks the explicit alternative routing that would earn a 5.

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