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

With no annotations, the description carries the full burden, and it does disclose the two traits that matter most for a pure function: the output domain (1-7) with the Sunday=7 convention, and the fallback behavior when date is omitted. It also notes the signed-wallet trial constraint. It stops short of saying what happens on an unparseable date, which is the remaining behavioral gap.

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?

One front-loaded sentence delivers the return value and default before any elaboration, with no wasted clauses. The trailing '🆓 5 free trial calls per signed wallet' is promotional rather than operational, but it is brief and plausibly useful signal about access limits.

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-parameter deterministic helper with no output schema, the description covers what the tool computes, the value range, the Sunday=7 convention, and the default input. The only substantive omission is the expected date input format, which is minor relative to the tool's simplicity.

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 description coverage is 0% for the single 'date' parameter, so the description must compensate. It adds real meaning beyond the bare string type by assigning the parameter a role and a default, but it never specifies the accepted format (ISO 8601? free text?), which is the one detail an agent needs to call this correctly.

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 uses a specific verb+resource ('Returns the ISO weekday number 1-7 for date') and pins the odd Sunday=7 convention, so an agent knows exactly the computed value. It does not, however, name or contrast itself with adjacent siblings such as x402-iso-week, x402-day-of-week, or x402-week-number, leaving the agent to infer the distinction from the name alone.

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?

There is no explicit when-to-use statement, no when-not-to-use, and no alternative tool named. The only contextual cue is the optional-parameter default ('defaulting to the current date'), which implies but never states that omitting the date yields today's weekday. An agent must infer the routing decision from the name alone.

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