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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description's added value is the data provenance (U.S. National Library of Medicine RxNorm), the geographic scope limit to US brands, what the response contains (ingredients plus RxCUI codes), and the 1-credit cost. The one gap is guidance on what happens when a brand is not found in RxNorm, which for an open-world lookup is the most likely failure mode.

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 purpose, example output, provenance, and caveats are front-loaded in a compact block with no filler or repetition. The audience sentence ('useful for patients, travellers and pharmacy staff') is the weakest line, adding framing rather than actionable information, but it is short enough not to distract.

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?

With no output schema, the description carries the return-value burden and does so by naming the fields (ingredient names, RxCUI codes) and the source. For a single-parameter read-only lookup this is nearly complete; only the not-found / ambiguous-brand behavior is left unstated.

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 there is only one parameter, with the schema already showing the format ('the brand name (e.g. "Zocor")'). The description reinforces this with two example brand names and the US-only constraint, but adds no additional syntax or normalization guidance beyond what the schema states. Baseline 3 applies.

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?

Leads with a specific question form ('What is the generic name of this brand?') and states a concrete verb+resource: returns active ingredient(s) of a US brand-name medicine, with two worked examples (Zocor: simvastatin; Vytorin: ezetimibe and simvastatin). The direction of the mapping (brand -> ingredient) implicitly distinguishes it from siblings like drug_brand_names that go the other way.

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?

States the applicable population ('patients, travellers and pharmacy staff looking for the generic equivalent') and two explicit exclusions: it does not compare prices and does not say whether a generic is interchangeable for a given patient. It also gives a hard prerequisite ('Brand names must be US ones known to RxNorm'). It stops short of naming sibling tools such as drug_spelling_suggest or drug_name_match as fallbacks when the brand is unknown.

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