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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), and the description adds substantial context beyond them: 'Requires auth', the idempotency behavior in plain language ('A verified owner is returned again'), and the full failure surface (400 confirm_invalid/expired/locked, 404 owner_not_found/inbox_not_found). This is unusually rich for a mutation tool.

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 usage trigger, then inputs, return shape, and errors in a logical order. Every sentence carries information, though the 'Inputs:' sentence duplicates the schema and could be trimmed for a five.

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 3-param mutation tool with no output schema, the description covers everything an agent needs: precondition, auth requirement, return field list, idempotency semantics, and enumerated error codes. Nothing material 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%, so the schema already documents all three parameters, including that inbox_id accepts an id, username, or email. The description's 'Inputs:' sentence largely restates the schema rather than adding syntax or format detail beyond it, 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 (mark verified), resource (owner), and mechanism (6-digit confirmation code), and clarifies the downstream effect ('so they can receive updates and open tasks'). This distinguishes it from sibling cooper_add_owner (which registers) and cooper_wait_for_code (which polls).

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 an explicit trigger condition: 'Use this when a human received the 6-digit confirmation code.' That is a clear when-to-use. It does not, however, name an explicit alternative for the pre-code state (e.g., cooper_wait_for_code), so it falls short of full routing guidance.

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