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

With no annotations, the description carries the burden and does well: it discloses cost ('Free'), the exact audit scope, the DNS lookup limit of 10 and that a true count is computed, and that a grade plus fixes are returned. It stops short of stating rate limits, permissions, or that the operation is read-only.

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?

Two tightly packed sentences with no waste: scope and cost are front-loaded, then the checklist of checks and the return value. Every clause 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?

There is no output schema, but the description compensates by naming the return ('a grade and the fixes to make') and detailing every check performed. With full param coverage and complete audit scope, the definition is close to self-sufficient.

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 documented with an example in the schema. The description adds no format or syntax detail beyond what the schema provides, so a baseline 3 is appropriate.

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?

States a specific verb and resource ('Audit one sending domain') and enumerates the exact checks performed: MX hosts, SPF with includes expanded, DMARC policy with inheritance, and published DKIM keys. The singular 'one sending domain' implicitly differentiates it from the plural sibling audit_sending_domains.

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?

'Free' hints at cost context and the single-domain scope implies when it applies, but there is no explicit when-to-use versus audit_sending_domains, flatten_spf, or verify_email, and no when-not guidance. Usage is inferable but not stated.

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