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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds behavior beyond that: the concrete fields returned (id, name, plan, allowed_origins, editable) and the key semantic that the id is 'the value to pass as site to the other tools', which is non-obvious plumbing information.

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 sentences, zero waste, front-loaded with what the tool lists before moving to the returned fields and the call-order hint. Every sentence carries distinct information.

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 enumerates the returned fields and their downstream meaning, which is what an agent needs to chain into site-scoped tools. It stops just short of fully exhaustive return coverage (e.g., ordering or pagination behavior is unstated), keeping it at a strong 4.

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 to disambiguate and the baseline is 4. The description does not need to compensate for any schema gaps since schema coverage is 100% and the object is empty.

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 the Siteon sites') plus an explicit scope ('in this API key's account'). It also names the fields each record carries, so the agent knows exactly what this returns versus the single-site sibling fetch_site.

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?

'Call this first to find the site id' gives a clear entry-point instruction and explains why an agent would reach for this tool before others. It does not explicitly name fetch_site as the alternative for a known id, so it stops short of 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.