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

Annotations already cover safety (readOnlyHint=true, idempotentHint=true, destructiveHint=false), so the bar is lower. The description adds genuinely useful behavioral context beyond the annotations: the 2026-2027 coverage window, the weekend baseline, the exclusion of non-statutory closures, and the rule that Store Bededag is not a holiday from 2024 onward. It does not mention rate limits or data-freshness/authority of the source dataset beyond naming dataset_version in outputs.

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?

Purpose is front-loaded, but the entry is bloated with material that duplicates structured data: a full enumeration of output fields when an output schema exists, a formula restatement, a REST fallback URL and a docs URL. Phrases like 'Denmark Denmark' and 'use this when you need a deterministic...result' waste space. Roughly half the text earns its place.

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 single-parameter deterministic holiday check, the description supplies the coverage period, the weekend rule, the exclusions, and a policy note on Store Bededag. With an output schema present it need not enumerate return values, yet it does so redundantly; otherwise an agent has what it needs to call and interpret the tool 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?

Schema description coverage is 100% for the single date parameter, so the schema already carries the semantics and baseline 3 applies. The description repeats 'Inputs: date (date)' and supplies concrete JSON argument examples, which adds mild value but no format or constraint detail beyond the schema's date format and its own examples.

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?

The description states a specific verb (checks) and resource (a date against the Saturday-Sunday weekend baseline and exact 2026-2027 authority events) and names the territory. It is distinguishable from sibling calculators by territory, but it never explicitly differentiates itself from the very similar check_dk_working_day-adjacent siblings like count_dk_working_days or add_dk_working_days. The opening sentence is garbled ('deterministic Denmark Denmark nationwide statutory public holidays for 2026-2027 result'), which slightly obscures the purpose.

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?

There is an explicit 'Use this when...' clause instructing the agent to call the tool directly rather than answering from memory, and a 'Do not use' clause listing exclusions (collective-agreement, employer, sector, school, bank, local and customary half-day closures). However, the do-not sentence is truncated/ungrammatical ('Do not use this when nationwide statutory list only'), so the boundary condition is implied rather than crisp.

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