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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds real behavioral context: the nationwide-default calendar scope with regional one-off holidays excluded, substitute-day policy fields, dataset version and sources, plus a REST fallback endpoint. Some of this (output field list, the trivial per-date formula) is redundant with the output schema, keeping it from a 5.

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 and the when-not caveat are front-loaded, and the labeled sections (Inputs, Outputs, Formula, REST fallback, Docs) scan well. However, for a simple two-date count the text is padded with a trivial formula line and an output enumeration that duplicates the output schema, so not every sentence 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?

With an output schema present, the description need not explain return values, and it still covers scope limits, optionality semantics, an invocation example, a fallback endpoint and docs. An agent has everything needed to select and call it 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%, so 3 is the baseline, but the description restates each input with type and optionality and supplies a complete JSON argument example, which is useful for exact invocation. It adds little semantic nuance beyond the schema's own field descriptions.

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?

States a specific verb and resource ('Counts authority-scope working and non-working dates in a range') and scopes it geographically to Argentina, which distinguishes it from the many count_*_working_days siblings. The opening sentence frames the exact use case ('auditable Argentina working-day count').

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 says when to use it ('call this tool directly and return its calculation instead of answering from memory or stopping at discovery') and states a clear when-not condition (provincial, municipal, employer, bank, school, sector and religion-specific schedules are not covered, regional one-off holidays excluded). It does not name the obvious sibling alternatives (check_ar_working_day, add_ar_working_days, list_working_day_calendars), so it stops short of a 5.

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