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

readOnlyHint=true already tells the agent this is a safe read, so the description doesn't need to re-establish that. It adds the underlying Admin API route (GET /api/websites), which hints at an API-key-admin surface but does not state auth requirements, pagination, or result size for accounts with many sites.

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 compact clauses, front-loaded with the action and immediately followed by the practically important note about how the result is used. No filler.

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 input parameters and no output schema, the description's job is mostly to explain the payload's role, which it does by identifying hostnames as the values fed to other tools. It stops short of describing the shape of each website record, though that is a minor omission for a discovery call.

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 clarify beyond what the schema conveys; baseline for a parameterless tool 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 and resource (list websites of the Simple Analytics account) and adds the crucial semantic detail that the returned hostnames are what the other tools consume. This plainly distinguishes it from the stats/timeseries/breakdown siblings, which all operate on a hostname.

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?

"Good first call" is explicit sequencing guidance, and naming the return value as input for the other tools effectively tells the agent this is the discovery prerequisite. No sibling is named as a mutually exclusive alternative, but for a no-param discovery call there is little ambiguity to resolve.

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