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

It directly explains an otherwise confusing annotation combination: 'Reads or computes only; not marked read-only because each call is charged,' resolving the apparent tension with readOnlyHint=false. It also discloses cost ($0.003/call), the billing paths (x402 USDC or card key at /credits), the 25 free calls, and that failed calls are free — exactly the kind of context annotations cannot convey.

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?

Dense and front-loaded: the capabilities come first, then usage, then example, then pricing/auth caveats. The opening sentence is long and list-heavy, but every sentence carries distinct information.

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 no output schema, the description correctly enumerates the returned fields, and it covers auth, cost, and the read-only annotation rationale. Only timezone/ISO-week edge-case behavior is left unstated for what is a lookup tool.

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% and the schema already says 'Date or ISO timestamp (default today)', so the description need not repeat it. The added example `date=2026-10-18` gives concrete format guidance, but no timezone or edge-case semantics are added beyond the schema.

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 first sentence enumerates exactly what is computed for a date (weekday, ISO week/week-year, day-of-year, quarter, days in month, leap year, Unix timestamp, weekend flag), which is far more specific than a tautology. It does not explicitly contrast itself with siblings like `unix`, `date_add`, or `date_diff`, so an agent must infer the boundary.

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?

'Use for calendar and reporting logic' plus a concrete example implies the usage context, but there is no explicit statement of when NOT to use it or which sibling (`unix`, `date_add`, `date_diff`) covers overlapping needs. Usage is implied rather than directed.

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