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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds real value beyond that: the deterministic algorithm (so results are verifiable) and the '1 credit' cost, which is operationally relevant. It stops short of stating the return form (boolean) explicitly, though 'Checks if' strongly implies it.

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?

One tight sentence plus a parenthetical cost note. The core purpose is front-loaded and every clause earns its place by either specifying the rule or disclosing cost.

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 pure function with no output schema, the definition is essentially complete: it states the rule, the input, and the cost. The only minor gap is that the boolean return type is only implied, not stated.

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% and the single 'year' parameter is already documented with an example (2024). The description adds no syntax, range, or format detail beyond the schema, so the baseline 3 applies — the schema does all the parameter work here.

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 gives a specific verb ('Checks') and resource ('a given year') and pins down the exact rule applied (Gregorian: divisible by 4, century exception, divisible by 400). This is unambiguous and clearly distinct from the many generic 'calculate_*' siblings.

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?

Usage is implied by the narrow scope — an agent can infer it should call this when it needs a leap-year determination and nothing else. However, there is no explicit when-to-use/when-not guidance, no statement of alternatives, and no note that the rule is Gregorian-only versus other calendar conventions.

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