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

With no annotations, the description carries the full burden, and it does disclose a genuinely important trait: a 0.005 USD per-call x402 payment requirement, plus the split data sourcing (local for DK, Nager.Date otherwise). It omits return shape, year-range limits, and behavior when a country is unsupported.

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 tight sentences with the scope and the cost up front; every clause carries information. The sourcing sentence is secondary but still earns its place as reliability context.

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 two-parameter lookup with no output schema, coverage is nearly adequate: scope, cost, and source are all stated. Missing only a note on what a result looks like and any year bounds, which is a modest gap given the tool's simplicity.

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 100%, so the baseline is 3. The description does add scope to the 'country' parameter by enumerating the accepted region, but says nothing about the 'year' parameter's valid range or default.

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 the resource precisely (national public holidays, yearly) and the exact geographic scope (EU/EEA/Nordic plus CH, GB), which lets an agent distinguish it from dk_bank_days or eu_working_days on content grounds. There is no explicit sibling differentiation, so it falls short of a 5.

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?

The description never says when to pick this over eu_working_days or dk_bank_days, nor does it state prerequisites or exclusions. Only the coverage list implies usage, leaving routing between overlapping calendar siblings to inference.

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