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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description adds the useful fact that two distinct retrievals happen (a DNS TXT lookup plus an HTTPS fetch of the policy file), but says nothing about failure modes — e.g. what happens when no record exists or the policy file is unreachable/invalid.

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?

A single front-loaded sentence naming both resources read; no filler, no restatement of the title.

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 tool with full annotation coverage, the definition is minimally adequate. However, with no output schema, the description could reasonably hint at what comes back (policy mode, MX list, record presence) and at the fact that policy retrieval requires an HTTPS request, which an agent budgeting latency or sandbox permissions would want to know.

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 0%, but there is only one parameter and the description's 'for a domain' makes its meaning unambiguous. No added detail on format (bare domain vs. URL) beyond the schema's 253-char string constraint.

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 verb is specific ('Read') and the resources are named precisely: the MTA-STS DNS record and the published policy file. That distinguishes it from the many DNS/security-check siblings (check_dmarc, check_spf, check_tls_rpt), though it never names or contrasts with them.

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 prerequisites, and no mention of alternatives such as running a broader security audit or checking the related TLS-RPT/DMARC records first. The agent must infer the trigger condition from the tool name alone.

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