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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), so the description's added value is the ISO week convention and the non-obvious cross-year behavior that Jan 1 can belong to a week starting in the prior December. It does not say how results are returned or whether optional default-to-today affects output, but the domain semantics are the meaningful disclosure here.

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 tight sentences with no padding; the ISO example front-loads the convention that disambiguates the whole tool. The trailing marketing URL is the only element that does not earn its place.

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 zero-required-parameter, read-only calculator with no output schema, the description must name the returned values, and it does (week number, Monday, Sunday, day of year, days remaining). It is essentially complete, lacking only a note on return format.

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% and the single 'date' parameter already documents the YYYY-MM-DD format and the empty-defaults-to-today behavior. The description adds no syntax or constraint beyond the schema, so the baseline 3 applies.

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+resource ('Get the week number of any date') and enumerates the outputs (Monday, Sunday, day of the year, days left), which implicitly separates it from siblings like day_of_week_calculator or date_difference_calculator. It never names an alternative explicitly, so it stops short of full sibling differentiation.

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: the tool is a lookup for a single date, and the worked example ('January 1, 2026 is in ISO week 1...') implicitly signals the ISO convention rather than, say, US week numbering. There is no explicit when-to-use, when-not-to-use, or named alternative tool.

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