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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is clear. The description adds behavioral context about MX resolution and TLSA lookup at a specific DNS label, which is useful. However, it does not explain return value structure (despite an output schema existing) or edge cases (e.g., no MX records). With annotations covering the core behavioral traits, a 3 is appropriate.

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 sentences with no waste. It front-loads the core action and protocol details, then provides usage guidance, then distinguishes from the sibling tool. Every sentence 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?

Given the presence of an output schema (which reduces the burden to explain return values), the description is complete for a focused security check tool. It covers purpose, process, and sibling differentiation. Minor gap: it doesn't mention what happens if the domain has no MX records or if DNSSEC is not available, but these are implied by the task and the tool is part of a larger audit suite (scan_domain).

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% with all 3 parameters documented. The description adds value by explaining the domain parameter in the context of SMTP DANE checking and the force_refresh parameter with a usage hint ('Useful after DNS changes'). The format parameter's auto-detection is noted. This goes slightly beyond the schema baseline of 3.

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 specifies the verb 'Check', the resource 'DANE/TLSA certificate pinning for SMTP at port 25', and the exact process (resolve MX, look up TLSA records at _25._tcp.<mx-host>). It clearly distinguishes itself from the sibling tool check_dane_https by naming the alternative and the different port/protocol.

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 this tool ('when asked if SMTP connections are protected by DANE/TLSA pinning') and when to use the alternative ('For HTTPS DANE at port 443, use check_dane_https instead'). This provides clear context and exclusion guidance.

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