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

Annotations already cover the safety profile (readOnly/idempotent/non-destructive/openWorld=false), and the description adds genuine scope boundaries — which closures are not inferred, and the private-sector annual-leave caveat. It even gives the counting formula. The garbled 'Do not use this when nationwide full-day public-holiday layer only' sentence weakens clarity, and no auth/rate-limit context is offered.

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-loaded well with use/when-not before mechanics, but it is bloated: it re-lists Inputs that the schema already documents, re-lists Outputs that the output schema already covers, and duplicates the example already present in the schema. Multiple labelled sections add length without adding decision-relevant information.

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?

Given an output schema exists, the description need not explain return values, yet it additionally supplies the scope definition, the counting formula, excluded-closure caveats, and the REST fallback path. Nothing an agent needs to invoke it 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 description coverage is 100% (all four params documented, with a worked JSON example in the schema itself), so the baseline is 3. The description's Inputs list and JSON example merely restate the schema without adding format, default, or edge-case meaning.

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+resource: 'Counts authority-scope working and non-working dates in a range' with a Finland scope, which cleanly separates it from the check_* and add_* siblings. It never explicitly names an alternative tool (e.g. check_fi_working_day or add_fi_working_days), so routing relies on the country token in the name.

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?

Provides an explicit when-to-use ('auditable Finland working-day count') and a when-not paragraph enumerating what is not inferred (Midsummer Eve, employer/collective-agreement, sector, school, bank, Åland, Sámi, local closures). It also instructs to call it directly rather than answer from memory. No alternative sibling is named however.

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