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

Annotations already declare read-only, idempotent, non-destructive behavior; the description adds valuable operational context: data source and ~110 country coverage, national vs regional classification, per-call price, x-credit-token header requirement, free daily call, and no wallet/API key needed. No contradiction with annotations.

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?

The core purpose is front-loaded, and the remaining clauses carry useful source, relationship, input, and cost/auth details. It is dense but somewhat run-on; splitting around 'Required input: country' would improve scannability without losing substance.

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 simple two-parameter tool with an output schema, the description covers purpose, source, entry type detail, required input, and payment/auth path. The main gap is that year is optional in the schema but no default behavior is mentioned.

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?

The schema already documents both parameters at 100% coverage, including Country (ISO-2) and Year. The description adds little parameter meaning beyond restating that country is required, and it does not clarify format or default behavior for the optional year parameter.

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 action ('List public holidays') with clear resource scope (country and year), data source (Nager.Date), and a distinguishing trait (national vs regional entries). This makes it easy to differentiate from holiday-adjacent siblings without opening the schema.

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 connects this tool to business_days by noting the shared source and frames this as the choice 'for agents that need the raw calendar.' It gives clear context but does not fully spell out when-not-to-use or formal alternative selection criteria.

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