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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), but the description adds substantial context beyond them: it is snapshot-bound to 2026, dates beyond 2026 are unsupported, later decrees require a new snapshot, the two compensable public-sector days remain working days for tax purposes, and the result is not proof of an individual's roster. These are real behavioral constraints an agent cannot infer from 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 guidance is front-loaded, but the description is bloated with material that duplicates structured fields: an Inputs line repeating the schema, full JSON examples already present in the schema, and a full Outputs field list even though an output schema exists. The broken fragment 'Do not use this when choose calendar_scope and workweek explicitly' adds noise rather than clarity.

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?

Given an output schema exists, return values need not be explained, yet the tool otherwise covers scope, applicability limits, dataset versioning, year boundary, and the REST fallback plus docs link. An agent has everything required to call it correctly; the only surplus is the redundant outputs enumeration.

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 baseline is 3, but the description adds meaning: it clarifies that calendar_scope separates national holidays from compensable public-sector days and that workweek distinguishes five- vs six-day rosters, plus three complete JSON argument examples. This is genuinely additive over the schema, though it largely restates the enum semantics.

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 for a deterministic date check against Peru's weekend baseline and 2026 authority events, and distinguishes it from add_/count_ siblings. However the opening sentence is garbled ('deterministic Peru Peru 2026 national_statutory result'), so the actual purpose only becomes clear several lines later at 'What it computes'. Clear but not front-loaded with maximum precision.

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?

Explicitly states when to use it ('Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery') and enumerates when not to: essential services, private-employer adoption, compensating shifts, regional holidays, banking, school, tax and procedural deadline calendars. This is as close to explicit when/when-not/alternative routing as a catalog tool gets.

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