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

Goes well beyond the annotations (readOnlyHint/openWorldHint/idempotentHint) by disclosing the pricing model (x402 USDC on Base, $0.001 per successful call), the auth/payment flow, and the exact behavior on non-payment (a PaymentRequired object is returned). Also states 'No personal data', an important privacy trait for an agent.

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?

Three tightly packed sentences, front-loaded with the usage condition, then the return shape, then the payment caveat. Every sentence earns its place with no filler.

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 no output schema, the description compensates by describing the returned fields and count (~100 countries). Payment behavior, data provenance, and prerequisite usage are all covered, so an agent has everything needed to call it correctly.

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?

No parameters exist, so the baseline is 4; the description correctly spends its words on the return payload (countryCode + English name) rather than inventing parameter semantics. Nothing about parameters needs further explanation.

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 (discover/returns) and resource (every country Nager.Date covers, ~100, with countryCode and English name), plus the exact fields returned. Clearly distinguishes it from siblings holidays and holiday_check as the discovery/lookup prerequisite.

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?

Explicitly says 'Use before calling /v1/holidays or /v1/holidays/check', naming the conditions that select this tool over the sibling holiday tools. Nothing about when to invoke it 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.