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

Annotations already declare readOnly, idempotent, closed-world, so the bar is lower; the description still adds value by disclosing that weekends and public holidays are excluded, that local weekends are supported, that excluded holidays are returned, and that each call costs $0.002 USDC via x402 on Base mainnet — a pricing/authorization detail absent from all structured fields.

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?

Core behavior is front-loaded in the first sentence, followed by scope, use cases and price. It is a bit padded — the country/calendar lists repeat what the country parameter description already provides — but no sentence is wasted in a way that misleads.

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 three-parameter read-only calculator with fully described parameters and no output schema, the definition covers what is counted, what is excluded, that excluded holidays are listed, and the cost of calling. Only the explicit routing against sibling date tools 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 100%, so the schema already documents from (exclusive), to (inclusive, within 5 years) and country codes. The description only restates country breadth ('220+ countries', verified African calendars) without adding format or edge-case semantics for the date parameters beyond the schema.

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?

Opens with a concrete verb and resource: 'counts the business days between two dates in any of 220+ countries, excluding weekends and public holidays.' That is distinct from the sibling za_add_business_days (which shifts a date) and za_is_business_day (single-day check), though neither sibling is named explicitly.

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 supplies use cases ('SLAs, turnaround times, leave days and deadlines measured in business days'), which implies when the tool fits, but it never states when to prefer a sibling such as za_is_business_day or za_add_business_days, nor any exclusions or prerequisites.

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