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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond them: pinned snapshot semantics, observed/estimated source flags, coverage window, the exact day-by-day formula, and the REST fallback endpoint with a warning not to guess other paths.

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?

Front-loaded with usage guidance and well-organized under labels, but it is long and repeats the JSON example already present in the input schema, plus an output field list that duplicates the existing output schema. Most sentences earn their place, though a few are redundant.

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?

Covers scope limits (2026-2028 coverage), required inputs, a worked example, computation semantics, and a documented fallback for a low-complexity calculation tool. Since an output schema exists, the enumerated output fields are redundant but harmless rather than a gap.

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 coverage is 100%, so the schema already documents all three parameters (including enum, pattern, bounds, and unit), making 3 the baseline. The description restates the parameter list and adds only marginal detail (start date exclusion for non-zero offsets, working-day decrement rule), which is genuine but modest added meaning.

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 ('Adds or subtracts working days using the pinned OpenWorkdays national-scope reference for 246 country/territory codes') and distinguishes its 'broad reference' scope from official-authority, regional, and employer calendars. It never names the closest sibling tools (add_global_working_days, add_global_public_holiday_working_days), so the differentiation is conceptual rather than explicit.

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?

Gives explicit when-to-use ('when you need a broad 2026-2028 date offset'), explicit when-not-to-use ('direct official authority, regional/local or employer calendar, or dates outside published coverage'), and an operational directive ('Call this tool directly and return its calculation instead of answering from memory'). Nothing is left to inference.

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