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

With no annotations, the description carries the full burden. It usefully discloses the returned fact categories and the auth/pricing gate ('5 free trial calls per signed wallet'), but says nothing about error behavior, date-format handling, or determinism of the read operation.

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 compact sentence with the core subject front-loaded and pricing appended. No wasted wording, though the emoji/trial-call clause is tangential to invocation.

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 one-optional-param trivia tool with no output schema and no annotations, the description covers what it returns and the default-date behavior, which is most of what an agent needs. The missing date-format hint is the only notable gap.

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 0% on the single 'date' parameter, so the description must compensate. It does add real meaning by signaling the parameter is optional and defaults to today, but it omits the accepted input format (ISO, epoch, free text), leaving a gap the schema cannot fill.

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 ('Returns') and resource ('leap-year, century-year and weekday facts') for a date, which is concrete and distinguishable from single-purpose siblings like x402-is-leap-year or x402-day-of-week. It doesn't explicitly say how it differs from those siblings, so it falls just 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?

It conveys the two operating modes ('for a given date or for today'), which implies when each applies, but it never names an alternative tool or states when-not to use it. Usage is implied rather than guided.

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