email_domains_list

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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the bar is lower; the description still adds real value by explaining that compact defaults on because 'the full object embeds the whole SSL certificate record' — a payload-size rationale an agent cannot get from annotations. It also discloses the two underlying endpoints, so an agent knows the call shape changes with site_id.

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 resource definition, then routing, then downstream usage, then the compact rationale — every clause is load-bearing. Slightly dense with two endpoint paths, but nothing is redundant.

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-only list tool with no output schema, the description covers what is returned at a high level (compact vs full objects, presence of id) and how the returned id is consumed downstream. An agent has everything needed to call it correctly on the first attempt.

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 the baseline is 3; the description goes beyond the schema by tying site_id to a different API route and explaining why compact=true is the default rather than merely repeating the default value. That is genuine added meaning over the property descriptions.

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 and resource ('List email (mail) domains') and immediately disambiguates the entity as 'the containers that mailboxes live in', which separates it from dns_domains_list without naming it. The endpoint mapping (GET /api/email/domains vs the site-scoped variant) pins the semantics precisely.

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?

Explains the site_id branch conditionally ('or ... when site_id is given') and tells the agent what to do with the result ('Use the returned id as domain_id for mailboxes_list / mailbox_create'). It does not explicitly say when to prefer dns_domains_list instead, so the exclusion half of the guidance is inferred rather than stated.

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