add_domain

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

No annotations are provided, so the description carries the full burden, and it does well: it discloses that the call mutates state (registers and saves the domain) and that verification is initiated immediately with a named checklist (MX, SPF, DKIM, DMARC, blacklists). It does not say whether verification is synchronous or async, what happens on duplicate domains, or whether the operation is reversible/removable, which keeps it short of a 5 for an unannotated mutation tool.

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?

Front-loaded with the action, then the mechanics, then routing guidance — a logical order with no filler. The 'DO NOT' sentence is somewhat long, but each clause carries distinct routing information that an agent needs.

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 one-parameter mutation tool with no annotations and no output schema, the description covers the action, side effects, verification scope, and sibling routing well. The remaining gap is post-call behavior: nothing about duplicate-domain errors, verification latency, or what the caller gets back.

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 0%, so the description must compensate for the single 'domain' parameter, and it only partially does: it implies the value must be a domain the user owns and that gets added to the workspace, but gives no format guidance (bare apex domain vs. subdomain vs. URL, no protocol). The schema contributes only a maxLength constraint.

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+resource ('Connect a new sending domain to the workspace') and immediately elaborates the concrete action: registering, saving, and kicking off DNS/deliverability verification. It explicitly distinguishes itself from check_domain and list_domains, so an agent can route correctly without opening any schema.

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?

Contains explicit 'USE THIS when...' guidance for the intended scenario and two 'DO NOT use...' exclusions naming the correct alternative for each (check_domain for testing an external/unverified domain, list_domains for listing). Nothing is left to inference.

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