Check DKIM Selector

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds genuinely useful context beyond them: it returns the verdict, its explanation, and the published key record, and explains that no fix record is returned because the key is generated by the sending platform.

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?

Three front-loaded sentences with zero waste: usage triggers first, then scope, then return behavior. Every sentence carries distinct information — trigger, one-selector constraint, and the no-fix rationale.

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?

For a 2-parameter read-only tool with no output schema, the description covers what it does, when to use it, what it returns, and why it deliberately omits a fix. An agent has everything needed to call it correctly.

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%, so both parameters are already documented with examples (google, selector1, dotted form) in the schema itself. The description restates selector examples but adds no syntax or format meaning beyond the schema — 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 precise verb (Check) and resource (ONE specific DKIM selector on a domain), and explicitly contrasts with the sibling full scan whose common-selector sweep may miss the exact selector. An agent can tell it apart from scan_domain without opening either schema.

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?

Front-loads concrete triggering conditions — whether DKIM is set up for a sending platform, whether a specific selector exists, or why DKIM fails — and names the alternative (full scan) plus the condition selecting this tool. Nothing is left to inference.

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