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

Annotations already declare readOnlyHint and openWorldHint, but the description adds real value beyond them: the paid-call model ($0.002 USDC per successful call via x402, on Base/Solana/Arc) and the explicit guarantee that failed calls are not charged. It also discloses truncation behavior (first listing page only, no letter text), which an agent must know before calling.

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 dense sentences with zero filler: scope and payload fields first, then hard limits and pricing. Every clause carries information an agent would otherwise have to infer or discover by trial.

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-value explanation is unnecessary, and the description covers the remaining gaps: data vintage ("latest"), truncation, absence of letter text, and billing behavior. For a zero-required-parameter listing tool this is sufficient to call 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 coverage is 100% and both parameters already carry constraints (company-name filter 2–60 chars, limit 1–20 default 10). The description adds nothing beyond the schema for parameters, so the 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?

States a specific verb+resource ("Latest FDA warning letters from the FDA listing page") and enumerates the returned fields: company, center/program, subject, issue date, link. It is unambiguous against siblings, though it never explicitly contrasts itself with nearby tools such as gov_openfda_drugsfda or other regulatory feed tools.

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?

Gives clear scope boundaries a caller needs: "First listing page only; no full history and no letter text," which tells the agent when this tool is insufficient. It stops short of naming an alternative source for full history or letter text, so the when-not case is stated without a redirect.

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