Date difference

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

Annotations already cover read-only/idempotent/closed-world, but the description adds two things they cannot: a cost model (first 25 calls/day free, then $0.001 via x402) and the constraint that business-day counting applies only to date inputs. It does not mention date-ordering behavior if 'to' precedes 'from', which is the main remaining behavioral unknown.

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?

The core capability is front-loaded in the first clause, followed by mechanics, use cases, and pricing in a logical order. The first sentence is heavily parenthetical and dense, but no sentence is wasted.

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 explained; the description still covers units, business-day rules, holiday handling, cost, and the date-only restriction on business-day counts. That is enough for an agent to call this correctly given five fully documented parameters.

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 the half-open [from, to) interval, workdays default, and country holiday scope are already documented in the schema. The description largely restates those semantics ('weekdays in [from, to) minus holidays; pass country to exclude its public holidays') without adding format or edge-case detail beyond them.

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 and result ('how many days, weeks, months or business days between two dates or datetimes') and enumerates the output modes (calendar Y/M/D, totals, business days). It implicitly contrasts with the inverse sibling date_add, but never names any sibling 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 — age, tenure, countdowns, notice periods, working days until a deadline — which clearly frames the intended context. It stops short of saying when NOT to use it or naming an alternative tool such as date_add or business_day.

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