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

Annotations already cover read-only/idempotent/non-destructive safety, and the description adds real behavioral content beyond them: the exact algorithm ('move one day at a time; decrement only on status.is_working_day=true'), the covered authority scope, the explicit non-coverage of employer/CAO calendars, the REST fallback endpoint, and a docs pointer. That is unusually rich disclosure for a pure calculation tool.

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?

Content is front-loaded and chunked under clear labels (when-to-use, when-not, what it computes, inputs, outputs, formula, fallback, docs), so it scans well despite being long. The 'Example user requests' lines and the enumerated output fields are padding that could be dropped without loss.

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?

With an output schema present, the description need not enumerate return fields, though it partly does anyway; the critical gaps an agent would care about – coverage scope, exclusions, and the fallback path – are all covered. The only residual gap is the implied boundary against sibling check/count tools, which the description never states.

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% and both parameters (start_date, working_days) already document format and sign semantics in the schema. The description restates the inputs and repeats a JSON example that is already in the schema's 'examples', adding little meaning beyond it, 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?

The description gives a specific verb+resource and scope: 'Adds or subtracts Netherlands authority-scope working days in exact coverage,' plus a deterministic-offset framing that separates it from the many sibling calendars. It never explicitly contrasts itself with the closest siblings (check_nl_working_day, count_nl_working_days), so an agent must infer the boundary from the name alone.

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?

It states explicit when-to-use ('Use this when you need a deterministic Netherlands working-day offset') and an explicit when-not ('Do not use this when a public holiday is not automatically a paid day off... CAO, employment contract, sector... are not inferred'), including the Liberation Day edge case. It even tells the agent to call the tool rather than answer from memory or stop at discovery.

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