Date facts

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered by structured data. The description adds genuinely new context the annotations cannot carry: the x402 pricing model with a 25-call free tier and per-call charge, which matters for call batching. It says nothing about invalid-date handling or what timezone the derived facts assume.

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?

Three short sentences, front-loaded with the returned facts, then use cases, then the cost model. Every sentence adds distinct information; none restates the tool name or the annotations.

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?

Output schema exists, so the description need not explain return values, and it spends its words on the facts list, use cases, and pricing instead. For a single-parameter, read-only lookup this is sufficient to call it correctly.

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%, and the description adds no meaning about the single date parameter — no statement that it must be an ISO 8601 calendar date, no restriction on past/future range, no timezone basis. The schema's regex pattern and example do carry the format, so the description is not the sole source, but it leaves a real gap.

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+resource ('Calendar facts for a date') and enumerates the exact facts returned (day of week, ISO week, quarter, day of year, leap year, weekend), which functionally separates it from arithmetic siblings like date_add and date_diff. It never names a sibling explicitly, so it stops short of a 5.

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?

Gives concrete use cases in quoted form ('what day is', week numbers, fiscal quarters) so the agent can pattern-match a user request. It offers no exclusions or named alternatives, e.g. it does not say to use parse_date_text for free-form input or business_day for working-day counts.

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