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

Annotations already declare read-only/idempotent/open-world, and the description layers on substantial extra behavior: the $0.25 price, free refusal path (coverage_gap, no_charge), shared 3-calls/IP/day rate limit, api_key vs x402 payment mechanics, receipt semantics, and the disclaimer that it is not legal advice. This is far more than the annotations convey.

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?

Front-loaded with the single most important fact (PAID and what you get), then layers constraints. It is dense and slightly repetitive — the receipt/certified-extract distinction is restated in both description and schema — but given the pricing and SKU complexity most sentences earn their place.

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, full annotation coverage, and 100% schema description coverage, the description fills the remaining gaps an agent needs: cost, payment path, free-refusal behavior, rate limits, and how to verify the receipt. Nothing needed to invoke it correctly appears to be missing.

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 adds real meaning beyond the schema: 'named series must all be certifiable', the default selection (first certifiable of vat, policy-rate, minimum-wage), and that receipt only applies on paid success at no extra USDC. It meaningfully expands on the bare param descriptions.

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 noun-resource ('Country evidence pack: the full cited country brief plus up to 3 Ed25519-signed certified extracts'), immediately telling the agent what it produces and how it differs from get_country_brief and the certified-extract SKU. An agent can distinguish this from every sibling 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?

Gives strong operative context: PAID ($0.25), shares the 3 free calls/IP/day with answer tools, pass api_key or receive the x402 payment requirement, and refusals are free. It stops short of an explicit 'prefer this over get_country_brief when you need signed certification' rule, so routing to the closest sibling is left partly to inference.

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