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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower, and the description still adds meaningful context: the deterministic weekend baseline, the 2026-2027 coverage window, the fact that cantonal/municipal layers are not inferred, and the substitute-day policy surfaces. The explicit formula and the named REST fallback path add error-handling value beyond the annotations.

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 header sections (What it computes / Inputs / Outputs / Formula / fallback / docs) are reasonably front-loaded and scannable, but there is waste and noise: a duplicated 'Switzerland Switzerland', an incoherent 'Do not use this when federal layer only', and example request lines that mix a holiday name with a caveat rather than showing clean requests.

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 one-parameter, deterministic date-check tool with a full output schema and complete annotation coverage, the description supplies what an agent needs: coverage window, the weekend+authority-event rule, the explicit scope limitation, and a fallback endpoint. The listed output field names are redundant given the output schema, but nothing essential 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% for the single date parameter and the schema already carries format, required-field, and examples, so the structured data does the heavy lifting. The description adds only the inline JSON argument examples, which largely duplicate the schema's examples array.

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 body states a specific verb and resource clearly: "Checks a date against the Saturday-Sunday weekend baseline and exact 2026-2027 authority events." However the opening line is garbled ("a deterministic Switzerland Switzerland federal public holiday layer for 2026-2027 result") and the description never explicitly contrasts itself with the adjacent add_/count_/list_ ch siblings, so an agent must infer that 'check' means single-date evaluation.

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 a real exclusion (cantonal, municipal, employer, school, bank and exchange schedules are not inferred, because Swiss law permits cantons additional holidays), which is valuable scope guidance. But the operative negative line is mangled to "Do not use this when federal layer only." and reads as unparseable, so the when-to-use routing is only partially usable.

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