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

Annotations already declare readOnly/idempotent/non-destructive, but the description goes well beyond them: it discloses the calendar scope limitation (cantons may recognize additional holidays; cantonal, municipal, employer, collective-agreement, school, bank and exchange schedules are not inferred), the computation rule, and a REST fallback path with a warning not to guess another /api/* path.

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 answer is front-loaded with the decisive when/when-not guidance and organized under clear labels, so an agent can skim it. However some content is filler or redundant: the 'Formula' line adds nothing, and the second example request ('Count Switzerland working days around Cantonal holiday is not inferred') merely repeats the exclusion already stated above.

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 4-parameter counting tool with full schema coverage and an output schema, the description covers everything an agent needs: scope, inclusive/exclusive semantics of the range endpoints, non-inferred calendars, a REST fallback, and a docs URL. Listing the output fields is redundant given the output schema 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 start_date, end_date and the two inclusion booleans. The description restates the same inputs and adds a complete JSON argument example, but contributes no new meaning (formats, boundaries, or defaults) beyond the structured fields, which is the baseline-3 case.

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 and resource ('Counts authority-scope working and non-working dates in a range') for a named territory, which cleanly separates it from the check_* (single-date) and add_* (arithmetic) Switzerland siblings. The scope is pinned down further with the explicit 'federal layer only' exclusion.

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 gives an explicit when-to-use ('when you need an auditable Switzerland working-day count'), a directive to call the tool rather than answer from memory or stop at discovery, and a when-not-to-use case ('Do not use this when federal layer only') enumerating the schedules that are not inferred.

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