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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and openWorld, so the safety profile is covered. The description adds genuinely useful non-annotation context—the pricing model (free within the daily allowance, then $0.001 USDC per call via x402) and the 'Active'-only scoping—but does not explain what constitutes an active vs inactive NDC or any rate-limit specifics.

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 short, front-loaded sentences with no filler; the resource is stated first and the pricing caveat second. Efficient and scannable, though nothing is trimmed to the point of losing the pricing detail.

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 an output schema present, return values need not be described, and the single parameter is fully documented. What remains missing is the relationship to the near-identical sibling rxnorm__ndc, which matters more than usual given how close the names are.

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 coverage is 100% for the single required rxcui parameter, so the baseline is 3. The phrase 'clinical or branded drug' nudges toward accepted RxCUI types, but adds little beyond what the schema description already states.

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 resource ('Active National Drug Codes') and the input it operates on ('an RxNorm clinical or branded drug'), so the agent knows what comes back. It does not, however, differentiate itself from the singular sibling rxnorm__ndc, leaving the plural/singular distinction to be inferred.

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?

There is no explicit when-to-use guidance, no mention of alternatives such as rxnorm__ndc or rxnorm__properties, and no preconditions stated. The word 'Active' implies a filtering behavior but the description never says when this tool is the right choice.

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