list_domains

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, establishing safety. The description adds value by disclosing the output content (Verification status and DNS records), which is not present in the schema. It does not go into pagination behavior, but that is covered by the parameter descriptions.

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?

The description is two sentences, with the primary action stated first and the usage tip second. No filler or redundant 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?

For a simple list tool with high schema coverage and annotations, the description provides all necessary context: what is listed, what fields appear, and when to use it. The output schema is absent, but the description adequately conveys the return content.

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 schema covers 100% of parameters (page and limit) with descriptions, so the baseline is 3. The description adds no additional parameter-specific context beyond what the schema provides.

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?

The description uses the specific verb 'List' with the resource 'sending domains' and specifies the exact fields returned ('verification status and their DKIM/SPF/DMARC records'). This clearly distinguishes it from other sibling tools such as add_domain and verify_domain.

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?

The second sentence provides an explicit trigger condition: 'Check here first when a send fails with an unverified-sender error.' This tells the agent when to use the tool, though it does not explicitly mention when not to use it or alternatives, so it falls short of a 5.

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