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

Annotations exist, but the description adds information they cannot carry: a concrete per-call price ($0.001 USDC on Base) and the x402 payment mechanism, which also explains why readOnlyHint=false for what is otherwise a pure computation. It does not address idempotency or the deterministic nature of the result, so it is strong but not exhaustive.

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?

Front-loaded with the return facets, then usage, then cost in three tight sentences with no obvious filler. The cost sentence earns its place by disclosing a paid call. Slightly dense but efficient.

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?

There is no output schema, and the description compensates by enumerating the returned fields, which is exactly the missing information an agent needs. A one-parameter computation tool with this field list plus payment disclosure is close to complete.

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% — the single parameter already documents "Date or ISO timestamp (default today)" — so the baseline is 3. The description adds "for any date" but no format, range, or timezone detail beyond what the schema already states.

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 enumerates exactly what is computed (weekday, ISO week, day of year, quarter, days in month, leap year, Unix timestamp, weekend flag) for a given date, which is more specific than a bare verb+resource. It implicitly separates itself from the arithmetic siblings date_add/date_diff, though it never names them, so it falls short of full sibling differentiation.

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" implies a context but gives no when-not-to-use guidance and never points to the obvious alternatives (date_add, date_diff, unix, time, cron_next). The usage rule is inferable rather than stated.

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