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

With no annotations, the description carries the full burden of explaining behavior. It discloses the dynamic pricing mechanism (paying USDC equivalent of ETH amount plus a fixed fee) and the owner wallet auto-detection from x402 payment. The concrete example further clarifies the pricing model. While it doesn't mention reversibility or potential failures, it gives the essential behavioral context for this funding operation.

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 appropriately sized, with a clear main sentence, a pricing rule sentence, and a practical example. It is front-loaded with the primary purpose. The example adds value by concretizing the pricing, though it could be seen as slightly redundant with the schema's example. No unnecessary fluff is present.

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?

For a single-parameter funding tool, the description covers the essential aspects: what it does, how pricing works, and how the owner is determined. It is complete enough for an agent to understand the mechanics and likely outcomes. It does not specify edge cases like minimum amounts or failure modes, but given the presence of an example and clear pricing, it is sufficiently 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?

The input schema already provides a comprehensive description for the 'amount' parameter, including an example and explanation of the fee. The tool description adds a worked example of the cost implication, which is helpful but does not fundamentally expand the parameter meaning beyond what the schema already covers. With 100% schema coverage, the baseline of 3 is appropriate.

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 function: funding a custodial wallet with ETH for gas. The verb 'Fund' directly conveys the action, and specifying the resource (custodial wallet) and the specific use case (gas) gives it a clear purpose. It also distinguishes itself from siblings like fund_wallet by emphasizing the ETH-specific and x402-payment context.

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 clear context for when to use this tool: when you need to fund a custodial wallet with ETH for gas, paying in USDC. It does not explicitly name alternatives or exclusions, but the implied usage is evident from the wording. It also clarifies the auto-detection of the owner wallet from x402 payments, which helps the agent understand the intended flow.

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