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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces that ('Reads or computes only and changes nothing'). It adds genuinely non-structured context: the $0.01/call x402 USDC or card-key pricing, 25 free calls, and that failed calls are free while repeats are charged, which also explains the idempotentHint=false flag. It does not describe the response shape beyond the field enumeration, hence not a 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?

Three sentences, front-loaded with the full field list so the agent knows what it gets immediately. The pricing sentence is long and slightly run-on, but every clause (price, free tier, free failures, repeat cost) carries behavioral information rather than filler.

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?

For a single optional-parameter computation tool with no output schema, the description supplies the returned fields, the input format, the cost model, and a clear read-only guarantee. Nothing an agent needs in order to call it correctly is missing.

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 already documents 'Date or ISO timestamp (default today)', so the baseline is 3. The description adds a concrete format example (date=2026-10-18), which disambiguates acceptable input syntax beyond the schema text, justifying a small uplift.

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 the exact facts computed (weekday, ISO week number and week-year, day of year, quarter, days in month, leap year, Unix timestamp, weekend flag) for any date, which is specific enough to separate it from the many date siblings such as date_add, date_diff, date_zodiac, unix and time. The input example (date=2026-10-18) makes the resource concrete.

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' gives only implied usage context. No exclusions or explicit alternatives are named, even though the sibling list contains obvious confusables (date_diff, date_business_days, unix, holidays) whose boundary with this tool is left for the agent to infer.

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