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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does this well by explaining that the tool returns a URL for the user to open in a browser, and that it should be followed by a verification step. It also introduces a caveat (only for card payments). However, it does not mention any side effects (e.g., whether a Stripe customer is created) or potential error conditions, so a small gap remains.

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 three sentences long and every sentence contributes value: purpose, next step, and when to skip. It front-loads the main action and avoids redundant phrasing. No wasted words.

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?

The tool is simple (one optional param, no output schema), and the description covers the essential operational details: return type (URL), user action (open in browser), follow-up (verify via get_account), and exclusions (crypto wallets). For this complexity level, it is entirely 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 coverage is 100% and the schema already describes the 'mode' parameter and its two enum values with behavior. The tool description does not add new insight beyond what the schema provides, so the baseline of 3 is appropriate. It also mentions the default 'checkout' indirectly but doesn't enrich the parameter semantics further.

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's purpose: 'Get a checkout URL for the user to add a payment card.' This is a specific verb+resource combination. It also distinguishes the tool from any billing-related sibling, as no other tool in the list handles billing setup. The scope is further clarified by noting it's only for card payments.

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 explicit when-to-use guidance: 'Only needed for card payments - agents with crypto wallets can skip this and pay with USDC on Base via x402 protocol.' It also gives a concrete post-condition workflow: 'After they complete the form, call get_account to verify has_payment_method is true.' This clearly tells the agent how to proceed and when not to use the tool.

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