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

No annotations, so the description carries the burden. It does disclose the return content (weekday + business-day flag) and the per-call cost of $0.003, which is real added value, but omits any definition of 'business day' (weekends only vs. holidays) and says nothing about weekStartsOn affecting the result.

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 core question and followed by the use case and pricing in two short sentences. The parenthetical cost is slightly incidental but useful; no wasted text overall.

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 trivial pure-computation tool with no output schema and no annotations, the description is adequate: it names both outputs and the trigger scenario. The remaining gap is the ambiguity of 'business day' (holiday handling) and the lack of a stated rationale for weekStartsOn.

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% with only 2 parameters, so the schema already documents both date (YYYY-MM-DD) and weekStartsOn (enum with default). The description adds no parameter-level detail beyond the schema, making the baseline 3 appropriate.

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 query and its two results: the weekday a date falls on and whether it is a business day. This is clearly distinct from siblings like business_days_between or time_until, though it never names an alternative 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?

Provides a concrete usage context: check before scheduling work or setting a deadline that lands on a weekend. No when-not-to-use or named alternative, but the triggering scenario is clear enough to select the tool.

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