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

Annotations only declare readOnlyHint=true and openWorldHint=false, so the payment disclosure ($0.002 USDC on Base, x402 flow, PaymentRequired on unpaid calls, retry via _meta[x402/payment]) is real added behavior the agent could not otherwise know. It falls short of 5 only because the actual return value (a count? a breakdown?) is never described.

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 in the first clause, then exclusions, presets, payment mechanics, and example args in descending order of importance. It is a single dense run-on with heavy parenthetical nesting, but no sentence is 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?

For a 4-param read tool with an output-less schema and thin annotations, the description covers purpose, exclusions, preset vocabulary, payment/auth flow, and a worked example. The one real omission is what the tool returns, which no output schema exists to cover.

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% but the schema descriptions are near-content-free ('e.g. 2026-10-01', 'e.g. none'), so the description does the real work: it enumerates the preset values (oia|lgoima|building_act|rta) that the schema omits entirely and shows a concrete argument set. It loses a point for leaving the 'region' parameter completely unexplained.

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 (Count), resource (NZ working days), and scope (between two dates inclusive, excluding weekends and public holidays). The scope of exclusion plus the day-count semantics distinguish it cleanly from the sibling nz_working_days_add (which shifts a date) and nz_holidays without needing either 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?

Usage is implied rather than stated: the agent can infer 'use this to count, not to shift dates,' and the x402/payment retry instruction is genuinely useful invocation guidance. However, no sibling is named and there is no explicit when-not (e.g. when to prefer nz_working_days_add or nz_holidays).

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