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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior; the description goes further with UTC-only dates, Monday–Friday definition of a weekday, boundary semantics (start included, end excluded unless includeEnd; offset excludes start), the important caveat that public holidays are NOT excluded, and operational facts (free, no auth, rate limited). That is substantial context beyond the 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?

Two tight sentences with the core capability front-loaded and boundary caveats packed in; no filler and nothing repeated from the title.

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, so return values need not be described, and annotations carry the safety profile. The description supplies the ambiguity-prone rules (UTC, weekday definition, boundary inclusion, holiday exclusion) an agent needs to call and interpret the tool 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 baseline is 3, but the description adds real semantics the schema cannot express: what includeEnd actually changes at the boundary and that the offset count excludes the start date. It does not clarify direction/businessOnly beyond the enum, so it stops short of 5.

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 specific verbs (count, add, subtract) on a specific resource (weekdays/dates) and names both operating modes, so an agent knows exactly what it does. Sibling tools are unrelated (pricing, agreements, VAT), so no differentiation is required.

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?

The two modes imply when each applies (counting a span vs. shifting a single date), but there is no explicit 'use this when...' guidance or exclusion language. Since no sibling tool overlaps in function, the inference cost is low, keeping this at minimum-viable.

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