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

Annotations cover idempotency and open-world reach; the description adds concrete behavior beyond them — what the first call returns, the state transition to `verified`, and the exact criteria (ownership + DKIM + SPF) for that transition. 'Safe to call repeatedly' reinforces, rather than contradicts, the idempotentHint.

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 tight sentences, front-loaded with the tool's dual purpose and followed by the call sequencing. No filler, though the sentence structure is slightly denser than strictly necessary.

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?

An output schema exists, so return-value documentation isn't required, yet the description still summarizes what comes back on the first call (the DNS record set). Both invocation modes and the verification condition are covered, leaving no significant gaps.

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?

There is a single parameter fully documented in the schema (100% coverage) with an example format ('mail.example.com'), so the schema already does the work. The description adds no further parameter detail — 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 ('Add a sending domain', 'check its DNS') and makes the dual-mode nature explicit up front. No sibling tool overlaps with domain setup, so an agent can route here without ambiguity.

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?

Explicitly describes the call sequence: first call registers and returns records, second call (after installation) runs the live check, and verification requires ownership + DKIM + SPF. It doesn't name alternative tools, but no sibling competes for this task.

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