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

Adds real context beyond the annotations: auth requirement, the explicit negative disclosure that the API key is not returned, and three concrete failure modes (404 workspace_not_found for another parent, 403 permission_denied for a sub-account key and for an inbox-scoped key). This is exactly the behavioral detail an agent cannot infer from readOnlyHint/idempotentHint.

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 when-to-use clause, then labeled Inputs and Returns blocks, then error cases — easy to scan. 'Read-only; requires auth' partly duplicates the annotations and the return field list is dense, but with no output schema that list 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?

With no output schema, the description supplies the return shape ({id, name, inbox_quota, inboxes_used, account_id, api_key_prefix, created_at}), the sensitive-field exclusion, and the error taxonomy. Nothing an agent needs to call this 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 workspace_id parameter is already documented in the schema, so the description only repeats 'workspace_id (required)'. Baseline 3 is appropriate — the heavy lifting is done by the 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?

States a specific verb+resource ('get one sub-account') and pins the scope to workspaces created by the signed-in parent, which separates it from cooper_list_workspaces and from another parent's data. It also names the payload (inbox quota, inboxes in use), so an agent knows exactly what this returns.

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?

'Use this when you need one sub-account created by the signed-in parent' gives a clear triggering condition and the 404/403 cases tell the agent when a call will fail. It stops short of naming the alternative (cooper_list_workspaces) for enumerating multiple workspaces, so it isn't a full when/when-not routing guide.

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