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

No annotations are provided, so the description carries the full burden of disclosing behavior. It states the core operations but omits any details about assumptions (e.g., business days excludes weekends but not holidays), side effects (none expected), or edge cases like negative amounts for subtraction. For a pure calculation tool, this is a moderate gap in transparency.

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 a single concise sentence of ten words, front-loading the core functionality without fluff. Every word contributes to conveying the tool's purpose.

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?

The tool has 5 parameters, 2 enums, and no output schema. The description is too terse to clarify parameter relationships, such as which parameters are required for each mode. It also does not hint at return values. There is notable ambiguity: date2 is described only as 'for diff mode', yet business-days counting presumably also requires two dates. This is a significant completeness gap for an agent to invoke 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 100% (every parameter has a description), meeting the baseline of 3. The description itself adds no parameter-level detail beyond the schema's existing explanations. Since the schema already documents mode, unit, date1, date2, and amount adequately, the description does not need to compensate.

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 uses specific verbs and resources: 'calculate date differences, add/subtract dates, count business days'. It clearly enumerates three distinct operations, distinguishing it from more specialized siblings like age-calculator or countdown-timer. However, it does not explicitly name any alternative tool or exclusion, so it slightly misses the highest bar for sibling differentiation.

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?

The description offers no guidance on when to choose this tool over alternatives or how to select among the modes (diff, add, business-days). It does not mention prerequisites, such as the need for two dates in diff/business-days modes or amount+unit in add mode. This is essentially no usage guidance beyond the implied general purpose.

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