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

With no annotations, the description carries the full burden: it discloses plan gating and enumerates returned fields, which is real value. It does not state behavior when no domain is configured (null vs. empty), nor confirm the operation is non-mutating beyond the word 'Get', leaving gaps for a zero-annotation 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?

One front-loaded sentence with the resource and returned fields stated up front; every clause earns its place. The trailing parenthetical distinguishing sender_domain.reply_to from the top-level reply_to is dense but genuinely disambiguating.

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 read-only getter with two optional identifying params and no output schema, the description covers what is returned and the plan constraint, which is most of what an agent needs. Missing only the empty/unconfigured-state behavior.

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%, so both project_id and project_slug are already documented in the schema. The description never mentions either parameter or how to choose between them (0 required parameters), so it adds nothing beyond the schema — 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?

Specific verb+resource ('Get the custom sender domain ... configured for this project') plus an enumeration of the payload (DNS records, verification status, Reply-To override). It implicitly contrasts with configure_sender_domain/remove_sender_domain via the read verb, but never names those siblings, so the agent must infer the routing.

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 '(Starter plan and above)' qualifier usefully signals a precondition and that lower-tier projects will have nothing to return. However, there is no explicit when-to-use/when-not guidance and no pointer to check_sender_domain or configure_sender_domain, leaving the choice between the four sender-domain tools implied rather than stated.

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