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

Annotations mark readOnlyHint=false, which could mislead an agent into expecting a write; the description usefully clarifies 'Does not change DNS' and explains the real side effect (1 account credit consumed on a successful check). That cost disclosure is real value beyond the annotations, though it says nothing about rate limits or failure behavior.

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, zero filler, front-loaded with the action and scope; the caveats (no DNS mutation, selector requirement, credit cost) follow in descending order of importance.

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?

With no output schema, the description still needn't detail return values, and it covers the key call prerequisites plus the non-mutation and cost facts. 'Report issues' is a slightly vague characterization of the result, which is the only real gap for a 3-parameter read-style tool.

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 67%, and the one parameter leaving a real gap, selector, is already documented in the schema itself ('required when check is dkim'). The description's enumeration of record types and the selector rule mostly restates the enum and schema text rather than adding new semantics.

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 ('Inspect') plus the exact resources it operates on (MX, SPF, DMARC, DKIM records) and the outcome ('report issues'). This cleanly separates it from siblings like email_verify, ip_lookup, and phone_lookup, which query different resource classes.

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?

It establishes the DKIM preconditions ('DKIM requires a selector') and implies usage via 'user-provided domain', but never says when to choose this over email_verify or ip_lookup. No explicit when/when-not guidance for the sibling set.

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