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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior, so the safety profile is covered. The description adds value by detailing the returned metrics (number of Americans, fills, total spend, out-of-pocket), which tells the agent what kind of data to expect, and clarifies the population-wide scope. No contradictions with annotations.

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 sentences with zero waste. The first sentence lists the key outputs, the second gives a contrast and a use case. It's front-loaded with the most important 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 has no output schema, so the description carries the burden of explaining what it returns, which it does explicitly. It also clarifies the scope (one drug, national, not programme-specific) and the parameters are fully covered in the schema. There is nothing an agent needs to call it correctly that is missing, aside from possibly noting any data caveats, but that's not critical.

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%: both parameters (drug and year) are described, including defaults and examples. The description adds no extra parameter meaning beyond restating 'for one drug,' which is already implied by the drug parameter. Given the high coverage, a baseline score of 3 is appropriate.

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 verb and resource: it reports national prescription volume and spending for one drug, listing concrete metrics (fills, spend, out-of-pocket). It distinguishes itself from siblings like meps_top_drugs by emphasizing 'for one drug' and 'population-wide rather than a single programme,' so an agent can tell it apart without inspecting other schemas.

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 description provides clear context: it's population-wide, for one drug, and answers how widely used a medicine is and the patient cost share. However, it does not explicitly name alternative tools (e.g., meps_top_drugs, meps_conditions_for_drug) or state when not to use it. The context implies the use case, but exclusions are left to inference.

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