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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is well covered. The description adds context like 'Free public API' (suggesting no authentication or external service) and 'CNAME chain' (indicating it follows the full chain), but does not disclose details such as rate limits or error behavior. This adds some value beyond annotations but lacks rich behavioral context.

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 short sentences with no fluff. It front-loads the core action ('Resolve a hostname's CNAME chain') and adds a use case. Every phrase earns its place, making it highly concise and well-structured.

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 one-parameter, read-only tool with no output schema, the description covers the essential aspects: what it does, a use case, and the external API nature. It does not explain return behavior in detail, but that is not critical given the low complexity and strong annotations. It is slightly incomplete in not mentioning what happens if no CNAME record exists, but this is a minor gap.

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 input schema provides 100% coverage for the 'host' parameter with a clear description and example ('www.example.com'). The tool description does not add additional semantic meaning beyond what the schema already offers, so the baseline score of 3 is appropriate.

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 clearly states 'Resolve a hostname's CNAME chain' with a specific verb ('Resolve') and resource ('hostname's CNAME chain'). It also identifies a distinct use case ('debugging custom-domain CNAME setups'), which differentiates it from sibling tools like dns_record_lookup that likely handle multiple record types.

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 provides a clear context for use: 'Useful for debugging custom-domain CNAME setups.' This indicates when the tool is appropriate, though it does not explicitly mention alternatives or when not to use it. It implies a specific scenario without excluding other potential uses.

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