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

Annotations already cover the safety profile (readOnly, idempotent, not openWorld), so the description's added value is the non-obvious operational facts it discloses: runtime-provided calendar support, the algorithm being named in every response, and a per-call price of $0.05 paid over x402 in USDC on Base. Cost/payment requirements are exactly the kind of thing an agent must know before invoking and would not learn from the schema.

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?

Two tight sentences that front-load the conversion capability and appendix capabilities (Easter), then close with the billing fact. Nothing is padded, though the long enum-style calendar list makes the first sentence dense.

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?

With five optional parameters, full schema coverage and no output schema, the definition covers both operations, both target sets and the payment model. It stops short of describing error behavior (e.g. invalid dates, out-of-range years) or the response shape, which it partially compensates for by stating the algorithm is named in every response.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning the schema does not: it explains that 'islamic' is the tabular civil calendar while 'islamic-umalqura' is a distinct variant, and that Easter has both Gregorian and Julian (western/eastern) reckonings. It also discloses the response will name the algorithm used, which contextualizes the conversion parameters.

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 concrete verb (convert) and resource (Gregorian dates vs. other calendar systems and back), and enumerates the exact target calendars (Islamic tabular vs. Umm al-Qura, Hebrew, Japanese era, ROC, Buddhist, Persian) plus a second capability (Easter in Gregorian and Julian reckonings). No sibling tool overlaps this domain, so the scope is unambiguous on its own.

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 capability statement: use it to convert dates between calendar systems or to compute Easter. There is no explicit when-to-use/when-not guidance and no pointer to adjacent time tools (time_zone, time_business-days), though none of them appear to overlap, so the omission is minor rather than harmful.

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