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

The description discloses key behaviors beyond the sparse annotations: 'this never charges anything by itself', 'you cannot pay for them', and credits arrive in seconds after payment. It also explains the state-dependent behavior (subscription vs. top-up), adding significant value beyond the readOnlyHint/destructiveHint flags.

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 every sentence earns its place: the usage trigger is front-loaded, then behavioral details and state-dependent logic are covered, and it ends with a clear follow-up. No filler or 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?

With no output schema, the description explains what is returned (a Stripe Checkout URL), the payment flow, the two state-dependent behaviors, and the recommended next steps. An agent has all necessary information to invoke 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?

Although the schema already has 100% coverage, the description adds critical meaning: plan pricing and credit counts, that the 'plan' parameter is ignored for top-ups, and that topUpUsd only applies to accounts with an existing plan. This exceeds what the schema alone provides.

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 tool returns a Stripe Checkout URL and specifies the trigger condition ('when a tool fails for lack of credits or a plan'). It distinguishes itself from the sibling get_credit_balance by focusing on generating a payment link rather than checking balance.

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 explicitly says when to use the tool, defines behavior for both scenarios (no active plan vs. active plan), and provides a clear follow-up sequence ('check get_credit_balance, then run the tool again'). It also notes the agent cannot pay on the user's behalf, which is a critical usage constraint.

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