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

No annotations are provided, so the description carries the behavioral burden. It usefully discloses the boundary convention (start exclusive, end inclusive), which is real behavioral context, but says nothing about return type, invalid calendar ids, or what happens when end precedes start.

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?

A single sentence with zero waste, and the semantically important boundary rule is included inline rather than buried. Nothing to trim.

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 simple three-parameter counting tool with fully documented params and no output schema, the description covers purpose and range semantics. The only real gap is the return value (an integer count) and edge-case behavior for invalid ranges.

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 parameters are already documented (including the rich calendar-id format). The description adds meaning beyond the schema by specifying how start and end are treated (start exclusive, end inclusive), which the schema's bare 'Date as YYYY-MM-DD' does not convey.

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 gives a specific verb+resource ('Count business days between two dates') that an agent can distinguish from siblings like add_business_days or is_business_day. It does not, however, explicitly name those alternatives or clarify the boundary between counting and date arithmetic.

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 by the name and the stated range semantics, but the description offers no explicit when-to-use guidance or exclusions versus siblings such as add_business_days or is_business_day. An agent must infer the selection from the tool name alone.

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