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

Annotations already establish readOnly=true, idempotent=true, openWorld=true and destructive=false, so the safety profile is covered. The description adds genuinely non-structured context: a per-call price ($0.005) and the returned field set. It still says nothing about rate limits or result freshness, keeping it short of a 5.

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 short sentences, front-loaded with what the tool returns, then cost, then a copy-pasteable sample. Every clause carries information an agent can act on; nothing is padding.

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?

There is no output schema, so the description compensates by enumerating the return fields (spf, dkim, dmarc, mx, overallScore, overallStatus, recommendations), plus cost and a valid sample invocation. For a one-parameter read tool this covers everything needed to 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?

Schema coverage is 100% and the parameter is already documented as 'a bare domain name, e.g. example.com'. The description's sample payload {'domain': 'example.com'} merely restates that format, so it adds little beyond what the schema provides; baseline 3 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?

The description names a concrete resource set — SPF, DKIM, DMARC records plus overall domain email 'posture' — which is specific enough to separate it from domain_dns, domain_dnssec and domain_security_score. It lacks an explicit verb and never names a sibling it is distinct from, so it stops short of a 5.

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 reference to any alternative tool. The pricing line and sample call give operational detail but do not tell the agent when this tool is the right choice versus the other twelve domain_* siblings.

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