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

No annotations are supplied, so the description carries the full burden. It implies a non-mutating check and hints at the result (sending verification status, MX target), but never states the actual return shape, whether results are cached, whether verification is asynchronous, or any auth requirement beyond what the schema's account_key field already says.

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 sentences, front-loaded with what is checked and followed by the next-step routing. No filler; the second sentence earns its place by wiring the agent into the create_inbox/send_message flow.

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 two-parameter, read-oriented check with no annotations and no output schema, the description covers what is verified and what to do next. The main remaining gap is that it does not describe the response fields an agent would need to branch on (e.g., whether sending and receiving are reported separately).

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 description coverage is 100% and both parameters are documented in the schema (domain from add_domain, account_key or Bearer header). The description adds nothing about parameter behavior, so baseline 3 applies.

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 (Check) and two concrete checks on the domain resource: sending verification via DKIM/MAIL FROM and receiving via MX pointing at GetCourier. That is far more specific than the title, though it does not explicitly contrast itself with the adjacent verify_owner or add_domain tools.

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?

Gives clear sequencing: run this check, and once verified call create_inbox with domain and local_part, then send_message. This tells the agent where the tool sits in the workflow, but there are no explicit exclusions or alternatives for the case where the domain is not verified.

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