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), and the description adds genuinely new behavioral context: the exact calendar policy scope and what is explicitly NOT modeled, the enumerated return fields (calendar_scope, holiday_policy, substitute_day_policy, dataset_version, sources) and the REST fallback path. This is substantive disclosure beyond structured fields.

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 the decision rule and exclusion, then clearly labeled sections (What it computes / Inputs / Outputs / Formula / Fallback / Docs), which is easy to scan. It is somewhat over-stuffed: the Formula line, the Inputs list and the complete JSON example all duplicate information already present in the schema.

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?

An output schema exists, yet the description still names the key return fields and, more importantly, covers calendar-policy boundaries, a worked argument example, a REST fallback endpoint and a docs link. An agent has everything needed to select and invoke this tool without guessing.

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% and the schema already carries per-parameter descriptions, defaults and examples, so the baseline is 3. The description's 'Inputs:' enumeration and JSON example largely restate the schema rather than adding syntax, format or edge-case meaning (e.g. what happens if include_start_date is false and start_date is a holiday).

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+resource+scope: 'Counts authority-scope working and non-working dates in a range' for the 中国香港特别行政区 general/public-holiday calendar. This clearly separates it from sibling count_* tools for other territories and from check_hk_working_day (single-date) and add_hk_working_days (date arithmetic).

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?

Explicit when-to-use ('Use this when you need an auditable ... working-day count', 'Call this tool directly ... instead of answering the formula from memory') and when-not-to-use (statutory employee holidays, employer rest days, school calendars, bank/exchange closures are not inferred). No sibling tool offers this level of routing guidance.

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