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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds substantially more: price ($0.35), a shared 3-free-calls-per-IP-per-day quota, the free refusal path (coverage_gap, no_charge), the receipt opt-in mechanics, and an explicit 'not legal advice' disclaimer. That is exactly the extra context annotations cannot express.

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?

The purpose and price are front-loaded in the first sentence, and every later sentence carries a real constraint (refusal, quota, receipt, verification). It is dense and parenthetical-heavy, and the receipt/certified-extract disclaimer is partly duplicated in the schema, but nothing is genuinely wasted.

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 not be described, and the description covers the remaining agent-facing concerns: payment, refusal semantics, rate limiting, receipt behavior, and verification path. Nothing needed to invoke it correctly is 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 already 86%, so the schema documents most parameters. The description still adds meaning the schema lacks: the default window of 90 days and the pricing/behavioral consequence of passing api_key versus relying on x402.

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 concrete verb and resource — upcoming VAT, PAYE and corporate-tax due dates within a window, with weekend/holiday rolling and cited rules — so the agent knows exactly what comes back. It does not, however, distinguish itself from the close sibling get_filing_deadlines, so a sibling-selection ambiguity remains.

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 clear applicability context: verified rules exist for BR, CL, DO, the default window is 90 days, and anything unanswerable is refused free with coverage_gap. It also lays out the payment path (api_key vs x402 card checkout). It stops short of naming when to prefer a sibling such as get_filing_deadlines or compute_vat.

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