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

readOnlyHint already marks it as a safe read, but the description adds critical downstream context the annotations cannot: the response names the upgrade_plan value to emit and the rendered card performs the purchase, so the agent must not claim a payment happened. This is precisely the behavioral disclosure that prevents a damaging mistake.

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 resource, then the trigger conditions, then the caution. The parenthetical limit breakdown is slightly dense but every clause carries operational value, so no meaningful trimming is warranted.

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 still explains what the response contains (plan, credit balance, the upgrade_plan value) and how it is consumed. Nothing an agent needs to call and use this tool 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?

Zero parameters, so the baseline is 4. Nothing to document and the description does not need to compensate for any schema gap.

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: the user's plan, credit balance, and upgrade target. An agent can immediately tell this apart from sibling tools like update_my_profile or list_integrations.

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?

Explicitly says to call it before answering anything about pricing, plans, upgrading, credits or limits, and even enumerates the limit dimensions. This is exactly the when-to-use routing an agent needs, with no inference required.

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