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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context: authentication is required, and querying another account's inbox yields HTTP 404 inbox_not_found. It omits rate-limit or pagination behavior, but for a single-resource lookup that is minor.

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 use condition and kept to a few dense sentences. The enumeration of return fields is long but earns its place because there is no output schema; overall efficient with little waste.

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 compensates by listing the returned inbox object's fields (including the direct/approval values of send_mode) and documents the auth requirement and 404 failure mode. Nothing needed to call it correctly is missing.

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 single parameter is already documented as accepting 'Inbox id (inb_…), username, or full email address owned by this key.' The description's restatement of the same accepted formats adds no meaning beyond the schema, 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?

Names a specific verb (get) and resource (one inbox) and enumerates the fields it retrieves, which clearly separates it from sibling cooper_list_inboxes and cooper_update_inbox. An agent can tell immediately that this fetches a single existing inbox by identifier.

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 states the condition: 'Use this when you need one inbox's ... and you already have its id, username, or email.' This gives clear selection context, though it never names cooper_list_inboxes as the alternative when the identifier is unknown, so routing guidance is one step short of complete.

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