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

Annotations already declare readOnlyHint=true and idempotentHint=true, covering safety. The description adds value by specifying the exact return content ('exact DNS records and instructions') and its purpose (verification and routing), which gives the agent a clear expectation of the output. It does not contradict 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?

The description is a single, efficient sentence that front-loads the key action and resource. No fluff or redundant details. Every word 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?

The description covers the essential purpose and what it returns, which is sufficient given the tool's simplicity and the annotations' coverage of safety. It lacks an output schema, but the description explicitly states what it returns. Minor omission: it doesn't mention that the output may vary depending on the domain parameter, but the schema already clarifies that behavior.

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%: both parameters already have clear descriptions in the schema. The tool description does not add any additional semantics beyond what the schema provides. Baseline of 3 is appropriate when schema fully documents parameters.

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 states a specific verb ('Return') and resource ('exact DNS records and instructions') and the purpose ('to verify and route the app custom domain'). It clearly distinguishes from siblings like check_domain_verification (which likely checks status) and get_domain_ssl_status by focusing on the records and instructions needed for setup.

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 description implies usage: call this when you need the DNS records to verify and route a custom domain. However, it does not explicitly name alternatives or state when not to use it. There's no guidance on choosing between this and check_domain_verification or get_domain_ssl_status, leaving the agent to infer based on the name and description.

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