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

Goes well beyond the readOnly/openWorld annotations by disclosing a hard bound (max 10 years), determinism ('no AI'), the return shape (count plus weekday holidays in range), and commercial behavior (x402 USDC pricing, 5 free calls/day/client). Cost and rate-limit disclosure is exactly the context an agent needs before calling.

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 computation semantics and efficient overall, with each sentence carrying distinct information. The trailing pricing/limit clause is relevant but slightly bulky relative to the rest.

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 no output schema, the description still explains the return value (count, sign behavior, holiday list) and adds the operational constraints. An agent has everything needed to call it correctly and predict the result.

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; the description adds the counting convention itself — 'days after start up to and including end (inclusive=true also counts start)' — which clarifies what the two required date params actually compute. The calendars param semantics (joint intersection) are left entirely to the schema.

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 resource ('counts business days between two dates') and pins down the exact counting convention (days after start, up to and including end) on a joint calendar. The semantic detail is enough to distinguish it from add_business_days or is_business_day without opening a schema.

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?

Usage is implied through the counting semantics (inclusive flag, negative result when end < start), but no sibling is named and no when-to-use/when-not guidance is given. It also doesn't say which calendar to pick versus list_holidays or settlement_date workflows.

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