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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds one behavioral fact beyond that — the request is pinned to a fixed domain — but says nothing about the shape or size of the index returned, which matters because the tool takes no arguments.

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 short sentence with the resource front-loaded and the domain qualifier in parentheses. Efficient, though the parenthetical would carry more value if it stated why the domain is fixed.

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?

With an output schema present, the description need not explain the returned index, and with no parameters it need not explain inputs. The only real gap is the absence of any routing hint toward skims_sitemap_urls, but as a zero-arg, output-schema-backed leaf tool this is close to sufficient.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; per the rubric this is the baseline 4. Calling out the pinned domain is a reasonable substitute for the absent URL parameter.

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 names a specific resource (sitemap index) and scopes it to a pinned domain (https://skims.com), which tells the agent exactly what is returned. It doesn't explicitly contrast itself with the sibling skims_sitemap_urls, so the index-vs-URL-list distinction must be inferred from the word 'index'.

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 at all — nothing says whether this is for discovery of individual sitemap files or that skims_sitemap_urls should be used once the index is known. Usage is only implied by the resource name.

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