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

With no annotations provided, the description carries the full behavioral burden. It does disclose the exact decision rule (divisible by 4, 100, 400), which is genuine behavioral content for a pure predicate, but it never states the return type (boolean vs string), how errors/invalid input are handled, or that the call is a side-effect-free read.

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 functional sentence is front-loaded and wastes nothing, and the trial-call note is short. The trailing promotional clause (and emoji) adds no selection value but is brief enough not to obscure the 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?

For a trivial one-input predicate with no annotations and no output schema, the description still omits the most important facts: what it returns and how it differs from the existing x402-is-leap-year sibling. The rule disclosure helps, but an agent cannot fully predict input format or output shape.

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 0% for the single 'value' parameter, so the description must compensate and does not. It doesn't clarify whether 'value' is a year number, a date string, or an arbitrary string, nor how the string type interacts with the '-num' naming.

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 verb and resource ('Checks whether value is a leap year') and even names the algorithm (divisible by 4, 100, 400), so the operation is unambiguous. However, it never differentiates from the near-identical sibling x402-is-leap-year, and the '-num' suffix that presumably distinguishes this variant is left unexplained.

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 statement of when to use this tool versus the sibling x402-is-leap-year (or a date-based leap check), and no prerequisites or exclusions. The only usage-adjacent text is the pricing/trial line, which is a commercial note, not guidance.

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