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

Annotations already declare readOnlyHint, idempotentHint and a closed-world non-destructive profile, so the safety burden is covered. The description adds a genuine behavioral rule — bare 10-digit codes are matched only as listed and never zero-padded — which affects results in a way the schema does not reveal. It stops short of describing not-found/error behavior or result shape.

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 tight sentences with zero filler; the accepted-input formats are front-loaded and the edge-case matching rule follows immediately. Every clause carries information an agent can act on.

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 explaining what comes back and does so only in the brief phrase 'the package and drug'. For a lookup tool that returns a nested package/drug payload, an agent would benefit from knowing the returned structure or the not-found case.

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%, so the baseline is 3, but the description earns credit by enumerating the accepted hyphenation patterns (4-4-2, 5-3-2, 5-4-1) and stating the no-padding match rule, which is more precise than the schema's single 'Like 50580-488-10' example. The as_of parameter is not addressed in the description, keeping this below 5.

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 precisely what is returned ('the package and drug for an NDC'), so the agent knows the resource and payload shape. It does not, however, distinguish itself from close siblings like get_drug, get_packages, or lookup_rxcui that could plausibly serve overlapping needs.

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 when-to-use guidance at all — nothing says when to pick lookup_ndc over lookup_rxcui (the obvious alternative for code-system lookups) or get_drug/get_packages. All the prose is spent on input formatting rather than tool selection.

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