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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real substance on top: live public DNS via DoH, the specific outputs produced (MX hosts, SPF lookup count vs. the limit of 10, DMARC policy/reporting/alignment, DKIM keys, pass/warn/fail findings with fix and CSV report). External-dependency and scope facts are disclosed rather than left to inference.

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?

Three sentences, front-loaded with the trigger conditions and with zero filler. The first sentence is a long synonym enumeration, which is dense but earns its place for routing; slightly heavy on commas.

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?

Though an output schema exists, the description still usefully summarizes the returned findings, and it covers the external-DNS dependency, the SPF limit, and the exclusions. Nothing an agent needs to invoke it correctly is missing.

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%, so both parameters are already documented in the schema, establishing a baseline of 3. The description adds only marginal meaning, noting that DKIM results depend on 'the selectors you give' but offering no extra syntax, defaults, or failure guidance beyond the schema.

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 ('email DNS check') and enumerates the concrete artifacts it covers (DMARC, SPF, DKIM, MX) plus the mechanism (DNS-over-HTTPS). An agent can immediately tell this apart from the sibling lookup_dns_records.

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?

Opens with an explicit trigger list ('Use this when the user wants...') mapped to user vocabulary, then gives hard exclusions ('Do not use for internal DNS server visibility, full deliverability tests, or reading or sending mail'). Both the when and the when-not are stated.

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