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

Annotations already declare readOnlyHint/idempotent/destructive=false, and the description adds genuinely useful behavior beyond them: the lookups are DNS-only, no email is sent or stored, and — importantly — the returned records are untrusted text from the domain owner that must never be treated as instructions. That prompt-injection warning is high-value context an agent cannot get from structured fields.

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 sentences, zero waste, front-loaded with purpose and result, then the safety-relevant read-only and injection caveats. Every clause 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?

Although there is no output schema, the description states what the tool returns (an A–F grade with explanations), confirms the operation is read-only DNS, and warns about untrusted record content. Nothing an agent needs in order to call and interpret the result 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?

There is a single parameter, and the schema documents it fully (100% coverage) with an example ('example.com'). The description adds no format or edge-case detail beyond the schema, so the baseline 3 for high-coverage schemas applies.

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 (Check) and resource (a domain's email authentication posture), enumerating exactly what is inspected — SPF, DKIM, and DMARC DNS records — and what is returned (A–F grade). No sibling in the list does DNS email-auth checks, so an agent can route to it unambiguously.

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?

The description gives clear context for when this is the right tool: verifying a domain's email authentication posture. No exclusions or alternative tools are named, but none of the siblings overlap with this capability, so the lack of an explicit 'use X instead' clause is minor.

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