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

Annotations already state readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds genuine non-annotation context: a per-call price of $0.001 and the x402 payment mechanism, which materially affects invocation decisions. It does not mention any rate limits or failure behavior for invalid dates, keeping it below 5.

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?

A single sentence that front-loads the resource and enumerates outputs compactly, with the cost note appended. Nothing is redundant and nothing is buried.

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?

An output schema exists, so the description does not need to explain return values; the cost model is disclosed. What remains unaddressed is edge behavior, such as how invalid or out-of-range dates are handled, which matters slightly for a computation tool that takes a strict-pattern input.

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?

There is one parameter with 0% description coverage, so the description should compensate but only says 'for a date'. The schema itself carries a regex pattern and a concrete example (2026-11-07), so the expected format is still discoverable structurally. The description adds no timezone, range, or validation semantics beyond that.

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?

Names the resource (calendar facts for a date) and enumerates exactly which facts it derives: weekday, ISO week, quarter, day of year, leap year, weekend. That enumeration distinguishes it from siblings like date_diff or date_add without needing to name them. No explicit sibling comparison is made, 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?

Usage is only implied: an agent can infer it should call this when it needs derived calendar attributes for a single date. There is no explicit when-not guidance and no routing to alternatives such as parse_date_text (for turning text into a date) or date_add/date_diff (for arithmetic).

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