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

Beyond the readOnly/idempotent annotations, the description discloses the exact return payload (total, serious, non-serious, death counts, top reactions, source URL, FDA data date, retrievedAt), a causation caveat, the 400 error case, and critically the paid x402 flow with the retry parameter and an HTTP fallback. That is substantial operational context annotations cannot supply.

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?

Purpose and filters come first, then return shape, caveat, errors, and payment, so it is well front-loaded. It is dense and the payment/transport detail lengthens it, but each sentence carries information an agent needs.

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 fully covers return values, caveats, errors, and payment requirements. The only shortfall is absent guidance on choosing this over related FDA tools for a given question.

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 only 50% — since, until, and serious_only have no descriptions — but the prose compensates by naming the reaction filter, date range, serious-only restriction, and generic-or-brand drug naming. The limit parameter is only implied ('top reported reactions'), leaving one minor gap.

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 and resource ('FDA adverse event report counts (FAERS via openFDA) for a drug'), plus the accepted identifier forms and optional filters. The resource is clearly distinct from fda_drug_label and fda_ndc_lookup, so an agent can pick it without opening the schema.

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 a concrete use case ('drug safety signal checks and pharmacovigilance research'), which tells the agent when the tool fits. It does not state when not to use it or compare it to siblings, which keeps this below a 5.

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