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

Annotations only cover read-only/open-world safety, yet the description adds substantial uncaptured behavior: the x402 pricing model ($0.002 USDC, Base/Solana/Arc), the rule that failed calls are not charged, the 404-not-charged behavior for countries with no holiday data, and per-country weekend variations. These are exactly the operational facts an agent needs before invoking a paid endpoint.

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-loads the purpose, then mode semantics, then edge rules, then cost — a sensible order. The pricing sentence is long but every clause (asset, chains, failure policy) carries decision-relevant information, so little 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?

With an output schema present, return values need no explanation; the description instead covers the things the schema cannot: weekend rules per country, holiday data source, error semantics, caps, and payment terms. Nothing an agent needs to call this 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 100%, so the baseline is 3; the description earns an extra point by clarifying the counting semantics ('after `from` up to and including `to`') and the caps (5-year span, 3,650 days), which the schema does not fully articulate. It also disambiguates that `days` may be negative for subtraction.

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 resource ('working days for a country') and then precisely defines the two operations it performs (counting between dates, adding N days). It implicitly separates itself from the sibling `holidays` tool by noting holidays are what gets *skipped*, but it never names an alternative, so sibling differentiation is only partial.

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?

Gives clear in-tool routing: mode=between vs mode=add, each with its required inputs and caps. It does not address when to prefer this over `date_calc` or `holidays`, which is the main remaining gap for an agent choosing among siblings.

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