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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description doesn't need to repeat those. The description adds behavioral details: it returns all entries from the alphabetical index that point to a code, including primary, star, and additional key numbers, and explicitly calls it a 'reverse lookup.' This goes beyond annotations.

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 sentences, one German and one English, with the main action front-loaded and no unnecessary words. The bilingual note is helpful for international users without adding bulk.

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 two-parameter tool with an output schema, the description covers the purpose, what it returns, and the scope of key types. It lacks explicit mention of error handling or pagination, but these are likely covered by the output schema or annotations. Overall, it is sufficiently complete for an agent to call it correctly.

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% – both parameters have clear descriptions in the schema (e.g., code format and year default). The tool description adds overall context about the reverse lookup purpose but doesn't add per-parameter semantics beyond what the schema already provides. 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?

The description states a specific verb (liefert) and resource (Alphabetischen Verzeichnisses entries) and clearly differentiates from siblings: it is a reverse lookup by ICD code, distinct from icd10alpha_search (which searches by term) and from icd10_get (which retrieves code details). It also specifies the scope of key types considered (primary, star, additional, and second primary).

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?

Provides a clear use case: 'useful to see which clinical and everyday diagnosis terms a code covers.' This implies when to use it (when you have a code and need its terms). However, it does not explicitly mention alternatives like icd10alpha_search or state when not to use it, so it lacks an explicit exclusion.

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