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

With no annotations, the description carries the full burden and delivers: 'This call does not charge', 'No quota spend and no email', 'Fails when the account cannot open a portal', and the notable 'ACL is not consulted'. These are the side-effect, cost, and authorization disclosures an agent needs before calling.

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 dense but each sentence earns its place by tying an action to its return value, default, or constraint. The opening 'Payment helpers' is slightly vague, but action-by-action structure keeps it navigable.

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-action tool with no output schema, the description documents each action's return shape ('sku, amount, currency, periodDays, and the POST URL', '{url}', 'purchases and a cursor') and the relevant failure and cost behavior, leaving no material gap for correct invocation.

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% and the schema already documents defaults, enums, and the includeStripe merge behavior in nearly identical wording. The description restates defaults ('Default sku is pro_prepaid_30d') rather than adding meaning beyond the schema, so the baseline 3 is appropriate.

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 then breaks down all three actions with their exact effects: machine_pay returns MPP payment instructions, portal returns a Stripe Customer Portal URL, purchases lists payment history. It explicitly distinguishes itself from siblings bootstrap_agent and get_usage, so an agent can route correctly.

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 routes each action: 'Use action=machine_pay to...', 'Use action=portal for a Stripe Customer Portal URL', 'Use action=purchases to list...'. It also names prerequisites (top-up SKUs require active Pro), sibling ordering (bootstrap_agent creates the account first), and a failure condition ('fails when the account cannot open a portal').

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