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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: the counting convention ('the start date itself is not counted; day 1 is the next business day'), the exact holiday set (11 US federal holidays with observed dates), and the supported year range 2000–2100. These are the details that actually determine whether a call returns the expected date.

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 core definition, then use cases, then sibling routing, then edge-case semantics. Every sentence carries distinct information; nothing restates the title or 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?

For a read-only date calculator with an output schema, an agent needs purpose, counting convention, holiday behavior, and bounds — all present. Return values need not be described since an output schema exists.

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 100%, so parameter documentation is already complete and a 3 is the floor. The description adds interpretive value by clarifying the 'after (or before)' meaning of direction, the optionality of holiday skipping, and the non-obvious off-by-one counting rule for business_days.

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 ('Find the date that is a given number of business days after (or before) a start date') and immediately pins the scope with 'skipping weekends and optionally US federal holidays'. It is trivially separable from business_days_between and add_to_date, which it names explicitly.

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?

Gives concrete use cases ('due date 10 business days from now', delivery dates, deadlines, notice periods) and explicitly routes the agent elsewhere: business_days_between for counting between two known dates, add_to_date for calendar-year/month/week/day arithmetic. When-to-use and when-not-to-use are both covered with named alternatives.

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