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

With no annotations provided, the description carries the full burden of behavioral disclosure. It explicitly reveals the paid nature ($0.001), the x402 challenge behavior, and the requirement to pass x_payment to settle. It also notes configurable weekend and holidays. The main gap is that it does not describe the return format for each operation, which would be important for an agent consuming 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?

The description is a single well-structured paragraph that front-loads the critical payment warning, then enumerates the four operations and their key parameters. Every sentence is substantive, with no filler or redundancy, making it easy to scan for relevant operation details.

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 description covers the core logic (operations, payment flow) and the schema handles parameter documentation, but there is no output schema. The description does not specify the return value shape (e.g., a string for add/subtract, an object for diff), which is a notable gap for an agent that needs to interpret results. Overall, it is adequate for tool selection and basic invocation but not fully complete.

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?

The input schema covers all 11 parameters with 100% description coverage, so the description adds little semantic value beyond what is already structured. It does mention the ISO-8601 duration format and operation-specific parameter groupings, but these are also present in the schema. Thus, the baseline score of 3 is 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?

The description clearly identifies the tool as calendar date math and enumerates four distinct operations (add/subtract, diff, business-add, business-diff) with their respective inputs. This specific verb+resource pairing distinguishes it from sibling tools like timezone, cron, and rrule, making its purpose unmistakable.

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 gives concrete usage context by listing each operation and its required parameters (e.g., 'op='add'/'subtract' an ISO-8601 duration to a date'). It also explains the payment flow, guiding whether to expect a challenge or pass x_payment. However, it does not explicitly state when not to use this tool versus alternatives like diff or timezone, though the sibling context implies these are distinct.

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