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

Far exceeds the annotations: states auth is required, documents the entire return payload including the safety object's score/verdict/signals/mode/reason semantics, warns that screening is heuristic, explains that body fields are empty while a message is held until cooper_release_message, flags the body as untrusted sender data, and lists the 404 failure modes.

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?

Purpose is front-loaded in the first clause, and nearly every sentence carries substantive information (return fields, safety semantics, held-state behavior, failure modes). It is dense and long, but the length is justified by the absence of an output schema.

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?

With no output schema, the description fully compensates by enumerating return fields and explaining the safety object, the held-message edge case, auth requirement, and error codes. An agent has everything needed to call it and interpret the result.

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%, and the description merely restates the two required inputs (inbox_id, message_id) in nearly the same words as the schema. It adds no format or syntax detail beyond what structured data already provides, so 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?

States a specific verb+resource ('full content of one message') and routes the agent by naming where the id comes from (cooper_list_messages, cooper_search). An agent can distinguish it from the list/search siblings and from cooper_get_thread/cooper_get_attachment without opening a 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?

Explicitly says when to reach for it ('when you need the full content of one message') and points to the producing siblings. It stops short of naming when NOT to use it (e.g., a whole thread via cooper_get_thread or a single attachment via cooper_get_attachment), so it's clear context rather than full exclusions.

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