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

With annotations covering the safe-read/idempotent profile, the description still adds substantial non-obvious context: the paid-invocation model ($0.05 per successful call over x402/USDC on Base) and the return payload (result date, day count, first 1,000 skipped dates with reasons). These are behavioral facts an agent cannot infer from annotations or schema.

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?

Three sentences, front-loaded with the operation set, then the calendar-flexibility rationale, then the return shape and price. No filler sentences and no restating of 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?

For a 7-parameter tool with no output schema, the description covers operations, calendar semantics, and the return payload, and even discloses the payment requirement. An agent has everything needed to decide to call it and to interpret results.

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 the baseline is 3, but the description adds meaning the schema does not: it motivates the weekday-mask design (Friday-Saturday and Sunday-only weeks) and the explicit holiday list so callers understand why holidays are an argument rather than a table lookup.

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?

Names the specific resource (business-day arithmetic) and both operations (add/subtract N working days, count days between dates), plus the distinguishing detail of a caller-supplied calendar. This clearly separates it from sibling time_calendar and time_rrule.

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?

Explains the two operating modes and the conditions that govern them (op=add vs op=count, mask-driven weekends, explicit holiday list), and gives a rationale for why the answer is stable. It never states when to prefer a sibling tool instead, 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.