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

Annotations already provide idempotentHint=true and destructiveHint=false, so the description need not restate those. The description adds value by stating the return value (MX record) and the overall behavior (configuring routing). However, it does not disclose side effects like overwriting existing routing or DNS requirements, so transparency is adequate but not enhanced.

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, no wasted words. The first sentence immediately states the purpose and outcome, the second sentence declares the return value. Highly efficient.

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?

With 100% schema coverage, annotations, and no output schema, the description covers the core purpose and return value. It is nearly complete, though it could mention prerequisites like domain verification. Given the context signals, this is a strong description.

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% with clear descriptions for all three parameters. The description's text ('Configure inbound email routing for a subdomain') aligns with the schema but does not add new meaning beyond what the parameter descriptions already provide. 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?

The description clearly states the verb 'Configure' and the resource 'inbound email routing for a subdomain', and specifies the outcome 'replies land in the MisarMail unified inbox' and the return value 'MX record'. This distinguishes it from siblings like add_domain, verify_domain, and send_email.

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?

No guidance is provided on when to use this tool versus alternatives. It does not mention prerequisites (e.g., domain must be added via add_domain or verified via verify_domain), nor does it indicate when not to use it. The agent has no explicit context for decision-making.

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