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

Far exceeds the annotations: it discloses price ($0.35), the free coverage_gap/no_charge refusal path, the shared 3-free-calls-per-IP-per-day limit, the x402 fallback when no api_key is passed, and that a paid success can include an Ed25519 receipt verifiable via verify_answer_receipt. The 'not legal advice' disclaimer and the distinction from certified extracts are exactly the behavioral context an agent needs.

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 paid price and the core purpose, and every sentence carries a distinct obligation (coverage, refusal, billing, receipt). Some redundancy remains: the receipt/certified-extract caveat appears in both the description body and the schema, and the pricing/verification sentences could be tightened.

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 values need no prose, and the description still covers everything else an agent needs: price, payment modes, rate limits, coverage boundaries, refusal semantics, and receipt verification. Nothing material about invoking this tool correctly is left unstated.

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 already 86%, but the description still adds meaning: receipt is tied to paid successes only (unpaid 402 and free refusals exclude it) and api_key is described as bypassing x402 while remaining metered. It does not clarify country/tax/date interaction beyond what the enum and descriptions provide.

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 names a specific verb and resource (upcoming VAT/PAYE/cit due dates in a window) with concrete scope: weekend/holiday rolling and an enumerated country set. It differentiates itself from related SKUs like the series certified extract, but never explicitly distinguishes itself from the close sibling get_filing_deadlines or get_calendar.

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 states the conditions that make the tool usable: the verified-country list, the default 90-day window, the free refusal path for anything not answerable in full, and how api_key vs x402 payment works. It stops short of naming an alternative tool for callers whose country is not covered, so the routing guidance is implied rather than explicit.

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