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

Annotations already declare readOnlyHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description does add real context by disclosing that weekends and public holidays for 100+ countries/regions are skipped and that custom weekend days are supported, but says nothing about return shape or how the holiday database is selected.

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 first two sentences are redundant restatements of the tool name/title, consuming prime front-loaded space without adding information. The useful content (holiday coverage, custom weekends) only appears in the trailing sentence.

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 five-parameter, read-only, no-output-schema tool, the description covers the key domain behavior (weekend/holiday skipping, 100+ country coverage, custom weekends). It is reasonably complete; the main omission is any statement of what the call returns or how the count relates to the add/subtract sibling.

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 all five parameters (start, end, country, state, weekend) are already documented in the schema. The description only echoes 'custom weekend days' and country coverage, adding no syntax or format detail beyond the schema, so baseline 3 applies.

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 core verb+resource ('count working days between two dates') is clear, but the description opens with two near-identical restatements of the title and then adds 'and add/subtract business days,' which blurs its purpose with the sibling add_business_days. An agent gets the gist but the scope statement undercuts itself.

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?

There is no when-to-use guidance and no mention of the obvious alternatives (add_business_days, is_public_holiday, public_holidays) that appear in the sibling list. The claim that it can 'add/subtract business days' actively muddles routing rather than clarifying it.

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