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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds that it shows aliasing behavior, but does not disclose additional traits such as return format, potential errors, or rate limits. With annotations, the description is adequate but not enriching.

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 concise sentences, front-loaded with the action ('Look up CNAME records') and a brief explanation of the output semantics. Every word earns its place; there is no redundancy or 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?

For a simple read-only DNS lookup with one well-documented parameter and no output schema, the description is sufficient to convey purpose and reasonable expectations. It could be more complete by describing the output structure, but overall it provides adequate context for an agent to invoke the tool correctly.

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 has 100% coverage with a clear description of the 'domain_name' parameter including an example. The tool description adds a tiny bit of context ('Shows where a hostname aliases to') but does not significantly enhance the parameter understanding beyond what the schema already provides. Baseline 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 the specific verb and resource: 'Look up CNAME (Canonical Name) records for a domain.' This directly distinguishes it from sibling tools like MX, TXT, or PTR lookups by naming the exact record type, fulfilling the requirement for a specific and distinguishing purpose.

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 clear context that this tool is for CNAME record lookups and explains what it does ('Shows where a hostname aliases to'). However, it does not explicitly mention alternatives or exclusions, such as 'for general DNS records, use dns_lookup.' This gives a clear scope without explicit when-not-to-use guidance.

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