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

Annotations already declare the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), so the description's main added value is the workflow constraint that the domain is not production-ready until DNS is applied and verified. It does not address what happens on duplicate domain creation or other mutation side effects, so it adds modest context beyond the annotations.

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 short sentences, zero waste, with the action front-loaded and the critical DNS caveat immediately following. Nothing could be trimmed without losing 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?

With an output schema present, return values need no explanation, and the description covers the core action plus the key operational caveat. It could say more about duplicate-handling or the verify/apply sequence, but it is essentially complete for a simple two-parameter creation tool.

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%, with both name and inbound_enabled documented in the schema itself. The description adds no parameter-level meaning (e.g., it never mentions inbound_enabled or its effect), so the 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?

"Add a sending domain" gives a specific verb plus resource and distinguishes creation from siblings like list_domains and verify_domain. It stops short of explicitly naming those siblings or clarifying the sending-vs-inbound scope trade-off in any detail.

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?

The sentence "DNS must still be applied and verified before production sends" implies the follow-up workflow (apply_domain_dns, verify_domain), which is useful implied guidance. However, it never explicitly names those tools or states when an agent should choose this over alternatives, leaving usage to inference.

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