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

The readOnlyHint annotation already establishes this as a safe read, so the bar is lower. The description goes beyond it by disclosing the enterprise-plan prerequisite and the exact API endpoint, both of which affect whether the call will succeed.

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 clauses with no filler; the core action is front-loaded and the plan constraint and endpoint follow compactly. Every clause earns its place.

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 single-parameter read tool with no output schema, the description covers purpose, a prerequisite, and a hint at returned fields ('timezone, etc.'). Nothing critical is missing, though it could say more about the returned shape.

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 coverage is 100%, so the site_id parameter is already documented with format and example. The description only reiterates 'by its domain' without adding semantics, so the baseline 3 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 ('Get a single site by its domain'), and the phrase 'a single site' implicitly contrasts with the list variant. It does not name the sibling alternative explicitly, so it falls short of a 5.

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?

Usage is only implicitly conveyed through 'a single site' versus the sibling plausible_list_sites, which is never named. It does add a genuine prerequisite ('Requires an enterprise plan'), which is useful context, but there is no explicit when-to-use/when-not guidance.

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