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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description usefully defines business days as Monday–Friday, but omits a key behavioral trait: no holiday handling is mentioned, and there is no note on how the all-defaults call behaves. Adds some context, but not rich.

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, front-loaded sentences covering both modes, with a concrete worked example (January 2026 has 22) that adds real value. The trailing web page URL is non-essential but conventional.

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?

For a four-parameter, all-optional calculator with no output schema, the description conveys both operations and their outputs well enough to call correctly. It could still be more explicit about what is returned in each mode and the default-argument behavior.

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% with per-parameter descriptions including the negative-days convention and the mode enum, so the schema does the heavy lifting. The description only loosely implies the count/add modes and adds no format or constraint detail beyond the schema. Baseline 3 applies.

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 specific operations on a specific resource: counting Mon–Fri working days between two dates, and adding business days to a start date. The 'business days' framing implicitly separates it from calendar-day siblings like date_difference_calculator, but it never names an alternative tool, so differentiation is inferred rather than stated.

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?

It gives clear usage context for both modes — count for working-day totals, add for shipping or contract deadlines — which maps directly onto the mode parameter. There are no exclusions or explicit sibling routing (e.g. vs. date_calculator), so it stops short of a 5.

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