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

The description explicitly states this writes a new account inbox, matching readOnlyHint=false and idempotentHint=false. It adds valuable security behavior: the plaintext key is returned once and should not be echoed after the first show. This goes beyond the annotations, though it could also mention duplicate-handling or failure behavior.

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?

Two sentences, no filler, and the critical caveat about not echoing the key is included without bloating the description. The core purpose is front-loaded and every sentence earns its place.

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 two-parameter creation tool with no output schema, the description is largely complete: it covers the side effect, the returned value, and the security warning. The main gap is the unresolved relationship with cooper_create_inbox, which could leave an agent unsure which creation tool to invoke.

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 explains both parameters. The description adds minimal semantic value beyond reinforcing that the username becomes the email local part and that an API key is produced, which is the baseline expectation for a fully-described schema.

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?

The description clearly states the action (create), the resource (Cooper Email inbox), and the secondary output (API key). It is easy to understand what the tool does. However, it does not distinguish itself from the near-identical sibling cooper_create_inbox, so it falls short of a 5.

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?

The description implies this is for creating a new account inbox and returning an API key, but it gives no explicit guidance on when to choose this tool over cooper_create_inbox or other sibling tools. No exclusions, prerequisites, or alternative routing are provided.

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