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

Annotations already declare non-read-only, non-destructive, non-idempotent behavior, so the description need not repeat safety hints. The description adds the status categories and timing ('straight away'), but given readOnlyHint=false it does not clearly explain what, if anything, is changed by 'confirms a paid checkout' or any permission requirements.

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; the first front-loads the returned status categories and the second adds a timing/confirmation note. No redundant restatement, so it is appropriately sized.

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?

No output schema exists, so the description carries the return-value burden; it does enumerate the key status fields. It remains thin on error cases or write side effects, but for a zero-param status tool it is largely complete.

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?

There are zero parameters, so the baseline is 4. The description has no parameter semantics to add, and none are needed.

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 states a specific resource (billing/payment status) and enumerates the returned fields: credit balance, extra-mailbox subscription state, mailbox quota vs free limit, and pending checkouts. It is distinguishable from checkout-creation siblings through the phrase 'after you gave the user a checkout link,' though it does not explicitly name an alternative tool.

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?

It gives a clear trigger: use after giving the user a checkout link, and to confirm a paid checkout promptly. It does not explicitly state when not to use it or name the create_billing_checkout/get_credits alternatives.

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