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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Read-only' is partly redundant, but the description adds genuinely new context: auth is required, there are no inputs, and it enumerates the returned shape. It does not cover rate limits or error semantics beyond the 402 case.

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 this when' trigger followed by the return shape. The brace-delimited return enumeration is dense with an ellipsis, but since there is no output schema it earns its space.

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 no-arg read tool with no output schema, the description supplies the usage trigger, auth requirement, and the return fields, leaving nothing an agent needs to call it correctly unstated.

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?

Zero parameters, so the baseline is 4; the description reinforces this with 'no inputs', which is the only parameter-relevant statement needed for a no-arg tool.

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 resource and what it reports: the account's plan, monthly quota usage, and the reason a send or inbox create returned 402. That is far more than a restatement of the title, though it never names a sibling (e.g. cooper_upgrade_link) to sharpen the boundary.

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 trigger — 'Use this when you need to know the account's plan... or why a send or inbox create returned 402' — which tells the agent exactly when to reach for it. No 'when not' clause or alternative tool is given, so it stops short of a 5.

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