check_mx

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

Annotations already provide readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds behavioral context by explaining the tool identifies mail servers and provider, and references its role in scan_domain audit. It does not disclose additional operational details like caching behavior or freshness semantics (though the force_refresh parameter implies caching), but given the strong annotations, this is adequate.

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?

The description is three concise sentences with no fluff. It front-loads the purpose, then provides usage guidance, then contextual placement. Every sentence earns its place, and it is easy to scan.

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?

Given the tool has an output schema and comprehensive annotations, the description is complete for a simple DNS lookup. It explains the core function and when to use it. It could mention edge cases like missing MX records, but that is not essential given the schema and audit context. Overall, it adequately covers the necessary context.

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 all three parameters (domain, format, force_refresh) are already well-described in the schema. The description adds minimal parameter-specific value; it only indirectly refers to domain. With full schema coverage, the baseline is 3, and the description does not surpass that.

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 clearly states the specific action (look up MX records) and the resource (domain), and further explains what it reveals (mail servers and email provider). It also distinguishes itself from sibling DNS check tools like check_spf and check_dmarc by specifying its unique output. The mention of being part of scan_domain audit adds context.

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 explicitly states when to use the tool: 'Use when asked which email provider hosts inbound mail for a domain, or to see MX record configuration.' This gives clear use cases. However, it does not mention when not to use it or list alternative tools for comparison, so it stops short of a 5.

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