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

Beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true), the description discloses the crucial behaviors: it never charges a saved card, the owner must complete the returned provider checkout, and there is no automatic top-up or invoice. These are exactly the facts an agent needs before invoking a payment-adjacent tool.

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?

Purpose is front-loaded in the first sentence, and each subsequent sentence adds one distinct fact (no card charge, owner completion, retry key, budget, no auto top-up). No filler or repetition.

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 an output schema present, return values need not be described, and the description covers preconditions, mutation semantics, retry behavior, and budget intent for all three parameters. A brief note on failure/expiry of an incomplete checkout would make it fully complete.

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 0%, so the description must carry parameter meaning, and it explains request_key (reuse for retries/idempotency) and max_usd_cents (explicit owner-approved purchase budget). Only api_key is left to inference, which is self-evident.

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 states a specific verb (prepare a checkout) plus the exact resource and scope ($5/500-credit, owner-completed, funding-enabled). It is clearly distinguishable from siblings like request_monthly_credits or create_utility_account without opening any schema.

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?

"Only when funding is enabled" gives an explicit precondition, and "Reuse request_key for retries" tells the agent how to handle repeated invocation. It does not name an alternative tool for the funding-disabled case, so it stops short of full when/when-not routing.

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