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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real context beyond them: required auth and message_read scope, the inbox-scoped key constraint, and specific failure modes mapped to HTTP 400 invalid_limit / invalid_page_token. This is unusually rich behavioral disclosure.

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?

Dense but front-loaded: trigger first, then inputs, then return shape, then error codes. Nearly every clause earns its place, though some parameter restatement duplicates the schema and could be trimmed.

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?

Although no output schema exists, the description supplies the return shape ({object:'list', data, next_page_token}), pagination mechanism, auth requirements, and error behavior. An agent has everything needed to invoke and interpret this call.

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%, so the schema already documents limits, labels, inbox_id and page_token. The description restates ranges and semantics (default 50, every label must match) rather than adding new meaning; per the baseline rule for fully-covered schemas, this is a 3.

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+scope: 'drafts on one inbox or across the account.' This distinguishes it from cooper_get_draft (single) and cooper_list_messages (different resource) without naming siblings explicitly. Clear but no explicit sibling differentiation.

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?

Gives a clear when-to-use trigger ('when you need drafts') and a concrete modifier for scope: omit inbox_id for every inbox this key can see, and the note that an inbox-scoped key only sees its inbox. No explicit when-not or named alternative (e.g., cooper_get_draft for a single draft), so it falls short of a 5.

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