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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds only a note that it mirrors a REST GET endpoint, which conveys determinism/purity but nothing about defaults, output shape, or edge cases. Adequate but not rich.

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 lines with the operations front-loaded and no filler. The trailing URL reference is somewhat cryptic and doesn't earn its place as a behavioral note, keeping it from a 5.

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 3-optional-param computation tool with no output schema, the description should ideally convey the shape of results (e.g. weekday name, ISO week number, day counts). It names the operations but not their outputs, leaving the agent somewhat under-informed despite the simple scope.

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 'to', 'add', and 'date' with formats and defaults. The description adds no parameter-level meaning beyond that (e.g. which params combine for which operation), 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?

The description enumerates the concrete operations (weekday, ISO week, date addition, day/weekday counts), which tells an agent what the tool computes and separates it from siblings like utcNow and timeInZones. It lacks a crisp verb+resource framing, but the feature list is specific enough to classify the tool.

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 guidance on when to use this versus alternatives (e.g. utcNow, timeInZones), no preconditions, and no exclusions. The API URL reference is a spec pointer, not usage guidance, so the agent must infer when this tool applies.

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