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 network-access profile is covered. The description adds only subject-matter context about what MTA-STS enforces, not tool behavior such as lookup mechanics, failure modes for domains without a policy, or what the result contains.

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?

One sentence, front-loaded with the verb and resource, with no redundant filler. The trailing relative clause on encryption is mildly explanatory rather than operational, keeping it just short of maximal efficiency.

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 one-parameter read-only check with full annotations, the description is sufficient to invoke the tool correctly, but with no output schema the agent has no idea what comes back (policy presence, mode, max_age, MX hosts) or how a missing policy is signaled. A sentence on the return shape would close the 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?

Schema description coverage is 100% and the schema already documents the single 'domain' parameter, including that a URL or email address also works. The description adds nothing about parameter format or accepted inputs, so the baseline 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?

Names a specific verb+resource (check a domain's MTA-STS policy) and briefly explains what MTA-STS is, which is genuinely clarifying for an agent. It does not, however, distinguish itself from close siblings such as check_domain_email_setup or check_bimi, so the agent must infer the boundary from the tool name alone.

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?

There is no when-to-use guidance: no statement of when a targeted MTA-STS check is preferable to the broader check_domain_email_setup, no prerequisites, and no exclusions. The description supplies domain background ('forces encrypted delivery of incoming mail') but nothing that routes the agent between alternatives.

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