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

Annotations already declare readOnlyHint=true and idempotentHint=true. The description adds useful behavioral context beyond that: it states the returned data items (definition, synonyms, cross-references), the scale ('Covers 4,245+ rare diseases'), language support, and licensing/auth conditions ('no auth, unlimited free'). This goes beyond a bare read-only statement.

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?

Three sentences with no filler. The first sentence states the action and resource, the second details the return fields, and the third gives coverage, languages, and source. Every sentence earns its place, and the core behavior is front-loaded.

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 straightforward lookup with two parameters, the description is complete: it covers what the tool does, what it returns, how many diseases it covers, which languages it supports, and the source/license. An output schema exists and is referenced, so the description does not need to restate structured return fields. Nothing an agent needs to invoke 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 description coverage is 100% and both parameters (name, lang) are described in the schema. The tool description reinforces their meaning by saying 'by disease name' and listing the 12 supported languages encoded in the lang enum, but it does not introduce new parameter-level semantics beyond what the 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 uses a specific verb 'Search' with a clear resource ('Orphanet rare disease database') and enumerates the outputs (ORPHAcode, cross-references to ICD-10, OMIM, etc.). This clearly differentiates it from sibling tools like disease_epidemiology or disease_phenotypes, which serve different purposes.

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 conveys when to use this tool: when needing to look up a disease by name and retrieve coding-system cross-references. It does not explicitly mention alternatives or exclusions, but the listed outputs make the use case clear. That is adequate but stops short of explicitly routing away from siblings.

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