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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description layers on substantial extra behavior: exact price, free refusal on coverage gaps, per-IP free-call sharing, api_key metering, and the receipt option. These are precisely the operational traits annotations cannot 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?

Purpose is front-loaded, which is good, but the passage is a dense run-on that spends several clauses on pricing, receipts, certified-extract disclaimers, and legal caveats. The receipt explanation largely duplicates the schema's own receipt description, so not every sentence earns its 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?

An output schema exists so return values need not be described, and the definition covers payment, coverage scope, refusal semantics, and validation for a paid 7-parameter tool. What is missing is any steer toward the near-duplicate sibling, leaving ambiguity in a crowded family.

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 high (86%), so the baseline is 3, but the description adds genuine default semantics (the window defaults to the next 90 days) and clarifies the receipt toggle's effect on paid vs. unpaid results. The api_key/x402 interaction is also explained beyond the schema's one-liner.

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: upcoming VAT/PAYE/cit due dates in a window, with defaults (90 days), holiday rolling, and rule citation. It lists exactly which countries are covered, which is unusually concrete. It does not, however, distinguish itself from the similarly-purposed sibling get_filing_deadlines.

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 explains the payment path (api_key vs x402), the free-refusal condition (coverage_gap, no_charge), and a shared rate limit, which is real usage context. But it never says when to choose this over get_filing_deadlines or the calendar/holiday siblings, so the core routing decision is left to inference.

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