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

Annotations only declare destructiveHint=true; the description adds that the mutation is the creation of an external Stripe session and discloses the return shape { customer_id, url }. It does not explain what 'destructive' means here (no Autumn data is overwritten) or whether sessions expire, but it adds real context beyond the annotation.

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?

Three compact clauses: mutation warning front-loaded, then the concrete action, then the API route and return shape. No sentence is filler and the most important safety signal comes first.

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 three-parameter tool with no output schema, the description covers purpose, endpoint, and return value, which is enough to invoke it correctly. It stops short of stating preconditions (customer existence, Stripe configuration) or session lifetime.

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 all three parameters (customer_id, return_url, configuration_id) are already documented in the schema. The description adds no parameter-level meaning such as default behavior or whether configuration_id falls back to a default config, so baseline 3 applies.

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: 'creates a Stripe billing-portal session for a customer,' plus the underlying endpoint POST /v1/billing.open_customer_portal. The action is distinct enough that no sibling (attach_plan, get_customer, etc.) could be confused with it, though no sibling is named explicitly.

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 says what the tool does but never when to use it in place of alternatives, nor any preconditions (e.g. customer must exist, Stripe must be configured). The phrase 'for a customer to manage their subscription' hints at intent but gives no selection guidance.

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