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

Annotations only declare readOnly and closed-world; the description adds the genuinely important behavior that the tool is paid ($0.02 USDC via x402) and that an unpaid call returns payment requirements rather than data, plus the exact retry mechanisms (X-PAYMENT / PAYMENT-SIGNATURE headers or params._meta["x402/payment"]). This is the kind of context an agent cannot infer from structured fields. It stops short of saying whether the first unpaid response should be treated as an error, or whether the payment flow is idempotent across retries.

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?

Two sentences, front-loaded with the resource and scope, then the payment mechanics. Nothing is filler, though the payment instruction is dense and would read more cleanly split into its own sentence or list.

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 read-only lookup with no output schema, the payment path is well covered, but the description says nothing about the shape of the returned calendar (event names, date fields, year/country effect on results). An agent knows how to pay but not quite what it will receive or how the two parameters shape it.

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 description coverage is 0%, so the description carries the burden of explaining parameters, and it mentions neither 'year' (2025-2028, default 2026) nor 'country'. Critically, it does not explain what happens for the non-US enum values (CA, GB, DE, FR, AU) even though the listed holidays are US-centric, leaving ambiguity about whether other countries return local dates or the same US set.

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 states a specific resource (a curated Western retail calendar) and enumerates its headline contents (Thanksgiving/Black Friday/Cyber Monday, fixed gifting dates) plus the intended use (cross-border campaign planning). It does not need sibling differentiation because no sibling tool in the list overlaps with retail calendars.

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 through the 'cross-border campaign planning' framing, which tells an agent the general context in which to reach for it. There is no explicit when-not-to-use guidance, no statement of which countries the calendar actually covers versus the enum's six values, and no alternative named.

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