billing_subscribe

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

With no annotations provided, the description carries the full burden and does an excellent job. It discloses the return object (checkoutUrl, sessionId, tier, interval, amountUsd), the ongoing effect (credits refill User.credits each billing period), and a payment limitation (Link virtual card covers first invoice only, renewals need durable payment). This is rich behavioral disclosure.

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 sentences, front-loaded with the core purpose. The second sentence references the return shape, and the third adds a practical human/payment caveat. No filler; every sentence carries meaningful information.

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 subscription checkout tool, the description is complete: it explains what it creates, what it returns, how credits recur, and a payment method caveat. Even without an output schema, the return fields are enumerated. No critical operational detail 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?

Input schema covers 100% of the parameters with clear enum descriptions for tier and interval. The description adds no new syntax or format details beyond mentioning the return fields. Baseline 3 is appropriate because the schema already documents parameters well.

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 clearly states the verb and resource: 'Create a Stripe Checkout session for a PostKing subscription.' It also distinguishes itself from sibling billing tools (billing_topup, billing_wallet) by focusing specifically on subscription checkout, not wallet top-ups or tier listing.

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 provides a clear usage context: 'The subscription Checkout is best completed by a human,' which guides the agent to potentially hand off to a human. It does not explicitly name alternative tools like billing_topup, but the context is sufficiently clear. Lacks explicit 'when not to use' guidance, so not a 5.

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