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

No annotations are provided, so the description carries the full burden, and it discloses nothing: not whether the result is 365/366, whether leap years are considered, or whether it is a pure computation. This is the same failure mode as the 'Process' calibration case.

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?

It is short, but the brevity comes from duplication rather than economy: the same four words appear twice and convey zero information. This is under-specification, not conciseness.

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 single-parameter tool with no annotations and no output schema, the description still omits everything an agent needs: what the return value is, whether the input is a full date or a year, and how leap years are handled. The crowded sibling space makes that omission costly.

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 per the rubric the baseline is 3 even though the description adds no parameter information. The schema's own text ('Date to process') is itself thin about accepted formats, but the description does nothing 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 is a verbatim restatement of the tool name ('Days In Year: Days In Year'), giving no verb and no explanation of what is returned. It does not distinguish this tool from near-identical siblings such as x402-day-of-year, x402-days-in-month, or x402-weeks-in-year.

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, no prerequisite, and no mention of any alternative tool. An agent has no basis for choosing this over the many adjacent date-calculation siblings.

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