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

No annotations are provided, so the description carries the burden. 'Read-only' is a useful safety disclosure and the DNS name pattern clarifies what is queried, but there is no mention of behavior for a missing/invalid selector, error handling, or return format for what is a network lookup.

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 tight sentences with zero filler; the operation and its scope are front-loaded, and the selector-sourcing hint follows logically.

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-only DNS query with no output schema, the description covers purpose, input sourcing, and safety. It is nearly complete, with only error/empty-result behavior left unstated.

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, but the description adds genuine meaning: it explains that selector originates from the DKIM-Signature s= tag and shows how both parameters combine into the queried record name. That is beyond what the schema states.

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?

Specific verb+resource: 'Fetch a domain's DKIM public-key record' with the exact DNS name pattern (<selector>._domainkey.<domain>) spelled out, which cleanly separates it from spf_check/dmarc_check siblings. It does not name an alternative explicitly, so it stops short of a 5.

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?

Adds real context on where the selector comes from (an email's DKIM-Signature s= tag or a known default), which tells the agent how to obtain the input. However it gives no when-to-use vs. alternatives guidance relative to dmarc_check, spf_check, or email_posture.

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