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

Beyond the readOnlyHint annotation, the description discloses authentication ('Anonymous'), rate limiting ('rate-limited per IP'), refusal behavior ('private and reserved address space is refused'), and that warnings are produced for ineffective header values. These are meaningful operational traits an agent needs before invoking the tool, and they do not contradict the readOnly annotation.

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 front-loaded with purpose and packed with useful distinctions, but the first sentence is a long, sprawling enumeration of return fields. Given that an output schema exists, that list is denser than strictly necessary, though the remaining sentences about alternatives and operational constraints clearly earn their 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 tool with an output schema, the description covers purpose, alternatives, safety/operational behavior, and refusal conditions. Since return-value details are already handled by the output schema, nothing essential is missing for an agent to select and invoke it 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?

There is only one parameter and schema description coverage is 100%, so the schema already fully documents the domain argument. The description adds no syntax, format, or validation details beyond what the schema provides, making the baseline score of 3 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 gives a specific verb and resource ('Check a domain's HTTP Strict Transport Security configuration') and then enumerates exactly which HSTS properties are evaluated. It explicitly distinguishes itself from the sibling tools check_ssl and redirect_check, so an agent can tell what it does and does not cover without opening any schema.

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?

It names the alternatives directly and states the boundary: 'Reports the policy the site advertises, not the certificate behind it (check_ssl) and not the full redirect chain (redirect_check).' This is an explicit when-to-use/when-not-to-use statement that routes the agent to the correct sibling for certificate and redirect questions.

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