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

With no annotations, the description carries the behavioral burden. It discloses the return range (week 1-53) and implies a pure calculation, but does not mention date format expectations, timezone handling, error behavior, or that the date parameter is technically optional in the schema.

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?

Two short sentences, front-loaded with the purpose, followed by input and output. It is efficient and avoids wasted text, though the second sentence slightly repeats input/output information without further depth.

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 simple one-parameter calculator with no output schema, the description is nearly complete: it states what is calculated and the return range. It lacks date format guidance, but the overall complexity is low enough that this is a minor 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 description coverage is 100%, so the schema already documents the date parameter. The description adds only 'for a given date' and 'Provide date', which does not add syntax or format guidance beyond the schema's 'Date to process'.

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 states a specific verb and resource: 'Calculate the ISO 8601 week number for a given date.' It is distinguishable from generic week tools by specifying ISO 8601, though it does not explicitly name sibling alternatives like x402-week-number or x402-week-of-year.

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 when-to-use guidance, no exclusions, and no mention of alternatives. The instruction 'Provide date' implies usage but does not explain when an agent should select this tool over similar week-related siblings.

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