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

Annotations already cover read-only, idempotent, non-destructive and open-world behavior, so the description correctly focuses on things annotations cannot express: the US-only scope, the RxNorm upstream source, its known lag versus FDA listing changes, and the 1-credit cost. That is exactly the supplemental behavioral context an agent needs.

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 question opener front-loads the core purpose and each following sentence adds distinct information (outputs, audience, scope limits, cost). The middle sentence is a long run-on list of returned fields, which slightly hurts scanability but contains no filler.

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 burden of describing returns and does so thoroughly (status categories, RxCUI and name, vocabularies, monthly history). Scope limits, data-source caveats and credit cost round out everything needed 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% and the single parameter already documents both the 11-digit and hyphenated 10-digit formats with an example. The description adds nothing about input format or validation, so it sits at the baseline where the schema does all the work.

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 question and then states the exact operation: checks a US NDC against RxNorm and reports status (active/obsolete/alien/unknown), RxCUI mapping, source vocabularies, and monthly mapping history. This is far more than a restatement of the name, and the mention of RxNorm records lagging FDA listing changes implicitly separates it from the FDA-based sibling fda_ndc_lookup.

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?

It gives concrete use-context (pharmacy, billing and claims work on old or unfamiliar codes) and clear exclusions (no price, packaging or supply). It stops short of naming an alternative tool for those excluded needs, so the agent is told when not to use it but not where to go instead.

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