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

Goes well past the readOnly/idempotent annotations by disclosing UTC-only dates, Monday–Friday scope, holiday exclusion behavior, exact boundary semantics (start included, end excluded, offset excludes start), and operational facts (free, no auth, rate limited). These are precisely the traits an agent needs to avoid off-by-one and holiday errors.

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?

Five short sentences, front-loaded with the two modes, then boundary semantics, then operational constraints. Every clause carries information; nothing is boilerplate or repetitive of 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?

With an output schema present, return values need not be described, and the description covers the remaining gaps: mode selection, date format expectations, boundary rules, holiday caveats, and auth/rate-limit context. Nothing an agent needs to call this 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 coverage is reported at 100%, so the baseline is 3, but the description contributes real semantic value the schema's bare property names do not: it explains includeEnd's inclusive behavior, the offset's exclusive start, and implicitly what businessOnly governs (weekdays). Direction's add/subtract meaning is self-evident from the enum.

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 two concrete operations with clear verbs and resources: count weekdays between two dates, or add/subtract days. An agent can match the task to the tool instantly, and no sibling tool in the list competes for 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?

The opening sentence delineates the two supported modes, which is the main selection decision an agent faces, and the schema's oneOf enforces which params each mode needs. It stops short of explicit 'use this instead of X' routing, but no sibling overlaps this domain.

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