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

readOnlyHint already declares a safe read. The description adds meaningful behavior beyond that: it discloses the default (queries all partitions and merges results) and how the narrowing parameters change that, which is not derivable from the annotations.

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 tight sentences, front-loaded with purpose, then the return contents, then usage and narrowing. Every sentence earns its place with 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 output schema, the description carries the return-value burden and does so by naming both domain categories and giving a concrete example. Enough context to call it correctly and interpret the result.

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 clears that bar by explaining the default merge-across-partitions behavior and the effect of `partition`/`shared`, adding default-value semantics the schema doesn't state.

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 domains the user can host sites under') and immediately specifies the contents: shared hosting domains plus organization-owned custom domains. It also distinguishes its role from siblings by naming create_site as the downstream consumer of the returned domain value.

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?

Explicitly frames the use case: 'Use this to pick a `domain` value before calling `create_site`.' It also gives narrowing guidance for `partition`/`shared`, but stops short of stating when NOT to use this tool or any explicit alternative for other domain-related needs.

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