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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, covering the safety profile. The description adds modest context — live DNS lookups and an issues listing — but says nothing about rate limits, latency, or failure behavior, so its added value is limited.

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 record enumeration is dense and front-loaded with 'Free', and most of the sentence earns its place. 'No payment.' at the end merely restates 'Free' and is wasted space.

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 correctly compensates by enumerating what is checked and reported (records plus an issues list). For a single-parameter read tool with full annotation coverage, nothing essential is missing, though the return shape remains only loosely characterized.

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% and the single 'domain' parameter is already fully documented, including that an email or URL will also work. The description adds no syntactic or format detail beyond the schema, so the baseline 3 for high coverage 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 gives a specific verb (check/look up) and resource (a domain's email security) and enumerates the exact records retrieved (MX, SPF, DMARC, DKIM), so the agent knows precisely what it does. It does not explicitly differentiate itself from the domain-vs-address sibling 'check_email_address', leaving that distinction to inference from the name.

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 or when-not-to-use guidance and no routing to alternatives such as check_email_address, email_fix_plan, or email_security_score. The repeated 'Free'/'No payment' hints at a pricing consideration but never states the condition under which this tool should be chosen.

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