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

With no annotations, the description carries the behavioral burden and succeeds in explaining the counting convention, the intersection rule across calendars, and that non-business days are returned with reasons. It does not cover edge cases such as reversed date ranges or output structure in detail, but the core behavior is well disclosed.

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 description is front-loaded with the core counting convention and then adds only the calendar semantics and examples needed to invoke the tool correctly. Every sentence and example earns its place.

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 three-parameter calculation tool with no annotations or output schema, the description covers the essential semantics: date boundaries, calendar selection, and multi-calendar intersection. It could be slightly more complete about return shape or error handling, but it is adequate to call the tool correctly.

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 0%, so the description must compensate. It adds substantial meaning for calendars, including where to get valid codes, multiple examples, and the rule that a date must be open in every calendar; it also clarifies the start/end boundary convention.

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?

The description states a specific operation: counting business days between two dates, with a precise inclusive/exclusive convention and the calendar-intersection rule. It clearly distinguishes itself from related siblings such as add_business_days and is_business_day.

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 explains how to choose calendars, points to list_calendars for valid calendar codes, and gives concrete examples for FX, NYSE settlement, euro payments, and London banks. It does not explicitly say when to prefer a sibling tool, but the intended use case is clear.

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