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

Annotations already cover the safe, read-only, idempotent profile, so the description focuses on behavior the annotations can't express: the 26-selector scan width and the CNAME-delegation diagnostic for Microsoft 365. It does not describe the shape of the success/failure output, which matters because there's no output schema.

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 sentences, front-loaded with the core action, then selector semantics, then the notable failure mode. No filler; every sentence carries information.

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 simple two-parameter read tool with no output schema, this covers what it scans, when it scans, and what it reports on failure. The main remaining gap is a hint about what a successful result contains beyond key strength.

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 baseline is 3; the description adds value by quantifying the auto-scan (26 selectors) and naming representative selectors (google, selector1, k1), which the schema only gestures at.

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 ("find and validate a domain's DKIM signing key") and adds scope (key strength). This is clearly distinguishable from sibling checks like check_spf, check_dmarc, and check_email_authentication.

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?

Explains exactly when to leave the selector empty and what that triggers (26-selector auto-scan), which is practical usage guidance. It stops short of naming when to prefer a sibling tool such as check_dns or check_email_authentication for broader diagnostics.

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