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

Beyond the readOnlyHint/openWorldHint/idempotentHint annotations, the description adds critical behavioral context: the tool always checks the connected mailbox's own domain, takes no arguments, and requires interpreting each result's note rather than trusting a bare pass/fail. It also warns about DMARC p=none and DKIM selector edge cases, and distinguishes 'missing' from 'lookup FAILED'.

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 front-loaded with what the tool checks, then when to use it, then the interpretation caveats. Every sentence adds necessary behavioral or usage information, and the warning about interpreting notes is essential for correct invocation and result reporting.

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 zero-parameter schema, complete annotations, and absence of an output schema, the description covers all essential operational guidance: what is checked, when to use it, what cannot be done, and how to interpret results responsibly. An agent has everything needed to invoke it correctly and avoid common misinterpretations.

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?

There are zero parameters, so per the baseline this dimension gets a 4. The description reinforces this by explicitly stating the tool takes no arguments and always targets the connected mailbox's domain, which prevents an agent from inventing a domain parameter.

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 states a specific action ('Check the DNS records'), a specific resource (the connected mailbox's own domain), and the deciding records (SPF, DKIM, DMARC, MX). It also explicitly distinguishes the tool from any general domain-lookup tool by stating it cannot look up anyone else's domain.

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 gives concrete trigger scenarios ('when the user asks why their mail goes to spam, why a recipient did not get something, or whether their domain is set up properly') and an exclusion ('cannot look up anyone else's'). It does not name specific sibling alternatives, but the usage context is clear enough for an agent to select this tool correctly.

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