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

Annotations already establish read-only, idempotent, non-destructive behavior, and the description adds valuable context beyond that: public-domain source, no authentication required, unlimited free use, and supported response languages. It does not discuss no-match behavior, but the safety/cost profile is well covered.

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 deliver action, output details, example mappings, a usage scenario, language support, and source/auth context without filler. The most important information is front-loaded, and each sentence earns its place.

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 simple read-only lookup with a rich input schema and an output schema present, the description is complete enough to select and invoke correctly. It could add guidance on code format edge cases or no-match handling, but these are minor gaps given the strong schema and annotation coverage.

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 both parameters. The description adds code examples and notes Spanish support, but these largely mirror the schema's own examples and enum. It does not meaningfully extend parameter understanding 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 names a specific verb ('Look up'), a precise resource ('ICD-9-CM diagnosis code via the NLM MedlinePlus Connect service'), and concrete outputs ('topic titles, URLs, and plain-language summaries'). It also gives illustrative code-to-condition examples, making the operation unambiguous and easily distinguishable from sibling lookup tools.

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 gives clear context for when this tool is appropriate: 'Useful for legacy EHR systems still using ICD-9-CM coding.' It does not explicitly name alternatives or state when not to use it, but the ICD-9-CM framing provides enough guidance to route an agent away from ICD-10/RxNorm/SNOMED sibling lookups.

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