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

Beyond the readOnlyHint annotation, the description meaningfully explains behavior: the card shows current wallet balance, ChatGPT cannot run Stripe inside the iframe, the user must tap through to the external credits URL, and the expected follow-up is ucode_credits_status. This gives the agent an accurate mental model of what happens without overstating side effects.

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?

Four short, purposeful sentences front-load the primary action, then add the external-payment limitation, follow-up step, and agent alternative. Every sentence earns its place with no redundant filler.

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 empty input schema, an existing output schema, and readOnly/destructive annotations already provided, the description completes the picture by explaining the human flow, external URL, post-payment status check, and the correct sibling for agents. Nothing needed to select and invoke this tool correctly 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?

The input schema has zero parameters, so the baseline is 4. There are no parameter semantics for the description to clarify, and the description doesn't need to compensate for schema gaps because none exist.

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 action and resource: it 'Opens the Add credits card with the current wallet balance.' It also immediately distinguishes this visual picker from agent/bot billing by explicitly directing agents to ucode_agent_billing, preventing confusion with similarly named credit and billing tools.

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 gives explicit when-to-use guidance: this tool is for the human-in-the-loop visual purchase flow, while agents/bots should call ucode_agent_billing instead. It also provides the follow-up step to call ucode_credits_status after payment, which is concrete workflow guidance.

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