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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so the safety and idempotency profile is fully covered. The description adds minor context by saying it returns the live CNAME target, but says nothing about behavior when no CNAME exists or about resolution failures. Adequate but not rich beyond 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?

Two short sentences with zero waste: the usage condition is front-loaded and the return statement is a single tight clause. Every sentence 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?

For a single-parameter read-only lookup with full annotation coverage and no output schema, the description covers triggering and return intent. The only gap is what happens on a negative result (no CNAME present), which is minor given the tool's simplicity.

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?

Parameter count is 1 with 100% schema description coverage, so the schema already documents domain_name with an example. The description adds no format, normalization, or edge-case guidance for the parameter. Baseline 3 applies when the schema carries the full burden.

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+resource: looks up whether a hostname is a CNAME alias and returns the live target. It is distinguishable from siblings like ptr_lookup, mx_lookup, or txt_lookup by naming the CNAME record type directly. It does not explicitly contrast with the broader dns_lookup sibling, so it falls short of a 5.

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?

Gives a clear triggering condition ('when the user wants to know whether a hostname is an alias of another one') plus concrete examples (verifying DKIM or tracking CNAMEs). No explicit when-not or named alternative tool, so no exclusions are stated.

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