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

Annotations already declare readOnlyHint/destructiveHint=false, so the safety profile is covered. The description goes beyond them by disclosing what the payload contains (login e-mail, last access) and decoding the null case ('ultimo_login: null = nunca entrou'), which is real behavioral context an agent cannot get from 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?

A single compact sentence with the resource first, the return payload second, and the null-value clarification last — nothing redundant. The emoji prefix is cosmetic but does not consume much space.

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 2-parameter read tool with no output schema, the description covers what the tool lists, the scope default, and the meaning of the notable null field. Pagination and total-count behavior are left unstated, but that is a minor gap for a low-complexity list 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 coverage is 100%, so baseline is 3; the description earns an extra point by explaining the semantics of omitting target_user_id (falls back to the authenticated account), a behavior the schema does not state. The admin-only restriction is already in the schema and is not repeated here.

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 ('Lista os contatos que têm acesso ao portal do cliente nesta conta') and previews the returned fields (login e-mail, last login). It is easily separable from create_portal_access/revoke_portal_access by the read verb, though it does not name those siblings explicitly.

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?

Adds one genuinely useful usage rule: without target_user_id it lists the caller's own authenticated account, which frames the default scope. However it never states when to prefer this over list_contacts or get_contact_360, nor any exclusions, leaving alternatives to inference.

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