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

The description discloses key behavioral traits: it 'Returns the verdict, its explanation, and the published key record when one resolves' and explicitly states 'No fix record is returned' with a rationale about DKIM key generation. This adds substantial context beyond the readOnly/openWorld/idempotent annotations, making the tool's output and limitations transparent.

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 two sentences, front-loaded with the core action, and every clause earns its place. It efficiently conveys purpose, distinguishes from alternatives, describes outputs, and explains the absence of a fix record without wasted words.

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 tool has only two parameters, a rich input schema, an output schema, and comprehensive annotations, the description fully covers the necessary context: what it checks, when to use it, what it returns, and why no fix record is provided. There are no significant gaps in the guidance an agent would need.

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?

The schema already provides 100% coverage with detailed descriptions for both parameters (domain and selector), including the nuance that the selector is 'not guessable from the domain.' The description adds little beyond reinforcing that the selector is the exact one used by the sending platform, so the schema does the heavy lifting; the description only marginally extends the parameter meaning.

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 starts with 'Check ONE specific DKIM selector on a domain', a specific verb+resource+scope, and explicitly contrasts with 'a full scan's common-selector sweep may miss', clearly distinguishing it from sibling scan tools. It also clarifies what is returned (verdict, explanation, key record), leaving no ambiguity about the tool's function.

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 implies when to use the tool by stating it targets 'the exact selector the sending platform uses' that a full scan might miss. This provides clear context for choosing this tool over a broader scan, though it does not explicitly name an alternative or spell out 'when not to use' scenarios.

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