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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds real context beyond them: the data source (OpenWorkdays national-scope snapshot), the 2026-2028 coverage window, the counting formula, and the fact that holiday_estimated/substitute_day_policy fields exist, though it omits rate limits or latency expectations.

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 when-to-use and when-not-to-use, then computation, inputs, outputs, formula, and fallback, all clearly sectioned. It is somewhat verbose, restating the inputs and JSON example already present in the schema and enumerating all output fields despite an output schema existing.

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 a 5-parameter tool with an output schema, the description covers the selection criteria, range limits, data provenance, formula semantics, and even a REST fallback endpoint with a docs link. Nothing an agent needs to invoke it correctly 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%, so every parameter (start_date, end_date, territory, include_start_date, include_end_date) is already documented including format, enum, and defaults. The description restates the inputs and provides a full JSON example, which is convenient but adds little semantic meaning beyond the schema.

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+resource ('Counts working and non-working dates in a 2026-2028 range') and explicitly scopes it to national-scope reference counts. It also distinguishes itself from regional/local or employer-calendar siblings, so an agent can route without opening other schemas.

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?

Contains an explicit 'Use this when...' clause with the selecting condition (broad national-scope reference count, no regional/employer semantics) and a 'Do not use this when...' clause listing exclusions (official authority, regional/employer calendar, out-of-range dates). It even instructs the agent to call directly rather than answer from memory.

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