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

Annotations already declare readOnlyHint=true, but the description adds substantive behavior beyond that: the result scope is limited to what the API key can access, cursor pagination is used, and an enterprise plan is required. No rate limits or permission-error behavior are covered, so it is useful context rather than exhaustive.

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 short, front-loaded sentences with no filler; the scope and returned fields come first. The trailing API endpoint reference ('Plausible: GET /api/v1/sites') is doc cross-reference rather than invocation guidance, which costs it a point.

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 no output schema, the description usefully names the shape of each returned record (domain + timezone) and how to page through results. It does not mention the pagination meta fields or approximate result counts, but nothing essential for correct invocation 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%: after, before, and limit each carry their own documentation including where cursors come from (meta.after/meta.before). The description's 'cursor pagination' phrase restates rather than extends that, so the baseline 3 is correct.

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 ('List the sites') plus the scope ('the API key can access') and the returned fields ('domain + timezone'). This clearly separates it from the single-site sibling plausible_get_site without needing to open either schema.

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?

Names a real gating condition ('Requires an enterprise plan') and explains the pagination mode, which tells the agent when the call is viable. It stops short of explicitly routing to alternatives such as plausible_get_site for a single site, so it is clear context rather than full when/when-not guidance.

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