check_mx

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

Annotations already declare readOnlyHint and idempotentHint, making the safety profile clear. The description adds that it identifies the email hosting provider, which is a value-added behavior beyond raw MX records. It also implies caching through force_refresh hint. No contradictions, but additional details (e.g., response format) are not needed due to output schema.

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?

Four sentences, each serving a purpose: main action, provider identification, usage guidance, broader context. No redundancies or filler. Front-loaded with the core function.

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 presence of an output schema, the description covers the essential aspects: purpose, usage context, and basic behavior. It leaves no major gaps for a simple DNS lookup tool. The reference to 'scan_domain audit' provides integration 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 coverage is 100%, so baseline is 3. The description adds value by explaining the force_refresh parameter as 'useful after DNS changes,' which provides context beyond the schema description. The format parameter is adequately described in 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?

The description explicitly states the tool looks up MX records for a domain, identifies mail servers and email hosting provider with concrete examples (Google Workspace, Microsoft 365, Proofpoint). This provides a specific verb and resource, and the mention of being part of a scan_domain audit helps distinguish it from other DNS tools, though sibling differentiation is implicit.

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?

Clearly states when to use: 'when asked which email provider hosts inbound mail for a domain, or to see MX record configuration.' Provides concrete context and mentions it is part of a broader audit. However, no explicit exclusion of alternatives or when-not-to-use.

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