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

Annotations declare the safety profile (readOnly=false, idempotent=true, destructive=false), and the description adds substantial context beyond that: auth is required, a below-usage quota is atomic ('changes nothing'), and it enumerates the exact failure modes (409 quota_below_usage, 404 workspace_not_found, 403 permission_denied for both sub-account and inbox-scoped keys). This is real behavioral value the annotations cannot carry.

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-loads the purpose, then inputs, then return shape, then errors — a sensible order. Slightly dense and the two 403 permission_denied cases are listed as separate sentences where one would do, but every sentence carries information.

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?

There is no output schema, so the description's return-shape summary ({id, name, inbox_quota, inboxes_used, account_id, api_key_prefix, created_at}) is doing necessary work, and the error conditions complete the picture for a mutation tool. 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%, so the baseline is 3. The description largely restates the schema fields, though it does add marginal detail the schema omits — 'inbox_quota (optional integer, at least 1)' supplies a minimum bound not present in the schema's property description.

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 and resource ('rename a sub-account or change how many live inboxes it may hold'), which cleanly distinguishes it from siblings like cooper_update_inbox, cooper_create_workspace, and cooper_update_webhook. An agent can tell what this tool mutates without opening the 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?

Opens with an explicit when-to-use condition ('Use this when a parent should rename a sub-account...'), plus the auth prerequisite. It does not name a specific alternative tool or a when-not condition, so it stops short of the full routing guidance a 5 would require.

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