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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds useful behavioral context beyond those flags: the returned members include substance-level 7-char ATC codes via source_atc_code, and it notes the RxNorm catalog is US-centric while ATC identifiers are international.

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 front-loaded with the core purpose, then uses bullets for actionable uses, followed by a concise caveat about output fields and data scope. It is slightly longer than strictly necessary but every sentence adds useful information.

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?

The tool is simple with a single documented parameter, an output schema, and rich annotations. The description covers purpose, usage scenarios, output field details, and data-source caveats, so an agent has enough context to select and invoke the tool 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?

The schema already fully documents the single atc_code parameter, including the pattern and the behavior at different ATC levels. The description adds a concrete example and emphasizes the substance-level code in results, but the parameter meaning is already well covered by the schema.

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: 'List the drugs (substances) that belong to an ATC class.' It also gives concrete examples and distinguishes the tool's membership-listing purpose from sibling tools like atc_lookup and atc_classify.

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' bullets provide clear scenarios: enumerate class members, build lists by pharmacological mechanism, and explore ATC subtrees. It does not explicitly name alternatives or exclusion criteria, but the intended use cases are well communicated.

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