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

Annotations only provide false hints, so the description carries the burden. It discloses the core side effect (creating a portal session) and the possible return shape (success URL or error), but does not discuss permissions, idempotency, or whether any billing changes happen immediately.

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?

The description is compact and front-loads the essential action and return type in the first sentence, then gives the portal context and error format. Every sentence carries relevant information with no redundancy.

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 parameterless action with no output schema, the description covers the operation, the user-facing capabilities of the portal, and the return contract. It lacks explicit alternatives or side-effect caveats, but nothing essential is missing for calling it correctly.

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?

The input schema has zero parameters, which warrants a baseline of 4. The description adds the useful return payload shape ('portal_url' or 'error'), and there are no parameter semantics to clarify.

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 names the specific action ('Create a Stripe Billing Portal session') and resource, and clearly states it returns a URL. It is unambiguous but does not explicitly differentiate this from related subscription tools like start_checkout or cancel_subscription.

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?

The description implies the use case by explaining the portal lets the user update payment method, view invoices, and download receipts. There is no explicit when-to-use or when-not-to-use guidance, nor any reference to sibling alternatives, so usage guidance is only implied.

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