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

The description thoroughly explains the tool's behavior: the two-step payment flow, the meaning of response codes (202 PENDING_CONFIRMATION, 404 AGENT_TOPUP_UNAVAILABLE), and the account crediting mechanism. It also notes that the agent spends the account's credits, which is crucial context. No contradiction with annotations (readOnlyHint false, destructiveHint false).

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?

Although long, the description is tightly structured and information-dense. It flows logically: purpose, when to use, steps, error handling, and retry guidance. Every sentence carries necessary content, and the structure makes it easy to follow despite its length.

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?

Given the tool's complexity (two-step payment, external blockchain interaction, potential error states), the description covers all necessary aspects: triggering conditions, procedure, response codes, retry behavior, and fallback instructions. It is complete for an agent to use correctly without additional context.

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% with both parameters (pack_key and payment_tx) described in detail. The description adds meaning by explaining the enum values (pro, pro_plus, business) with credit amounts and costs, and by clarifying the role of payment_tx (omit on first call, include on second). This goes beyond the schema's own descriptions.

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: 'Top up the ACCOUNT's credit balance by buying a package with USDC on Base.' It specifies the verb (top up), resource (credit balance), and method (buying a package), and distinguishes it from sibling tools by focusing on credit purchase and when to use it (402/409 errors).

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?

Explicitly states when to use: 'Use it when create_listing/gold/flare returns 402 (out of credits) or 409 (listing limit).' It provides a clear two-step procedure, including what to omit on the first call and what to include on the second, plus guidance on retry for pending confirmations.

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