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

Annotations already declare readOnly/idempotent/openWorld=false, but the description adds real behavioral context beyond them: the auditability guarantee, the list of schedules that are NOT inferred (CAO, sector, employer, school, bank, municipal), and the Liberation Day five-year/CAO dependency. The REST fallback path and docs link further reduce guesswork, though it does not disclose rate limits or failure modes.

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 with the use case and exclusion before the mechanical sections (inputs, JSON example, outputs, formula, REST fallback). It is long, but each block is labelled and skimmable; the output-field list and formula are slightly redundant given an output schema exists.

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 calculator with a full output schema, the description covers scope, exclusions, required inputs with a runnable JSON example, and a fallback endpoint. Nothing needed to call it correctly is missing; the output list is redundant but harmless.

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 schema already documents all four parameters and their defaults. The description restates the inputs and types without adding format, boundary, or constraint detail beyond what the schema provides, so the baseline 3 applies.

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+scope ('Counts authority-scope working and non-working dates in a range') for the Netherlands calendar, which distinguishes it from the 200+ sibling count_*/check_*/add_* country variants and from check_nl_working_day (single date). The explicit 'what it computes' line removes ambiguity about what is being counted.

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?

Gives an explicit use condition ('when you need an auditable Netherlands working-day count'), an instruction to call it rather than answer from memory, and an explicit exclusion ('Do not use this when a public holiday is not automatically a paid day off for every Dutch employee' with CAO/contract/sector caveats). This is a rare case of both when-to-use and when-not-to-use being spelled out.

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