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

It discloses the SimilarWeb v5 response envelope, the exact-3-month upstream constraint, the specific upstream errors (120 and 101), the rolling monthly window, and a practical example. This goes well beyond the readOnly/idempotent annotations and clarifies the main non-obvious behavior of the API.

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?

The description is dense and focused; the date-window guidance, error codes, and /describe pointer all earn their place. The opening one-word fragment 'SimilarSites.' is somewhat redundant with the title, but overall the section is tight and information-rich.

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 10-parameter tool with a strict rolling date constraint and an output schema, the description thoroughly covers the one truly non-obvious behavior, gives an actionable example, and points to /describe for state that changes monthly. The schema covers parameter defaults/enums and the output schema covers return values, so nothing essential is missing.

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 baseline is 3. The description adds real value for the date parameters—concrete example, exact error codes, and rolling-window semantics—rather than repeating schema text. Other parameters are left to the schema, which is complete.

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 name and title ('get_similarweb_similar_sites' / 'SimilarSites') make the resource clear and distinguish it from sibling SimilarWeb tools. However, the description itself never explicitly states a verb+resource action like 'returns a list of similar sites for a domain'; it opens with the one-word title and moves straight to response envelope and date constraints.

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?

The description gives concrete date-usage guidance: request the three most recent completed months, and call the /describe endpoint to discover the exact currently-supported range. It does not discuss when to prefer this tool over sibling SimilarWeb tools, but the context is clear enough to prevent obvious misuse.

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