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

Annotations already disclose readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the description only needs to add context. It adds meaning by explaining that results include constituent groups and code ranges, which is useful. However, it doesn't go deeper into response behavior, and the output schema already carries some of that burden.

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 with the core behavior and an illustrative example. The bullet list is useful and readable, though the final sentence 'Provide a chapter number (1-22)' repeats schema information and could be trimmed, keeping it from a 5.

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 low-complexity tool with one well-documented parameter, an output schema, and safety annotations, the description is largely complete. It explains the use cases and the returned chapter-group structure. It doesn't discuss sibling alternatives, but that isn't critical given the focused scope and available context.

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?

The input schema fully documents the single 'num' parameter with type, range 1-22, and a description, giving 100% schema coverage. The description merely repeats 'Provide a chapter number (1-22)' without adding new semantic detail, so the baseline score of 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 action — 'Get one CID-10 chapter and its constituent groups' — with a concrete example showing chapter IX expanded into ranges like I00-I02. It clearly distinguishes this from sibling tools such as cid10_chapters (which lists all chapters) and cid10_search/lookup by focusing on one chapter's hierarchical groups.

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 'Use this tool to' bullet list gives explicit contexts: drilling into groups, building hierarchical browsers, and finding which group contains a code range. It provides clear when-to-use guidance but does not explicitly mention when not to use it or contrast it with alternatives like cid10_search, so it stops short of a 5.

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