Cofferline

topup_balance

Top up the prepaid balance with USDC. Auth required. Payment flow: call once without x_payment — a 402 reply lists the exact EIP-3009 requirements (amount, USDC asset, recipient, EIP-712 domain). Sign a transferWithAuthorization for them outside MCP (this server cannot sign), then call again with x_payment set to the base64 of {x402Version:1, scheme:'exact', network, payload:{signature, authorization}}.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "amount_usd": "<amount_usd>"
    },
    "name": "topup_balance"
  }
}

Input Schema

Name	Required	Description	Default
`x_payment`	No	base64 X-PAYMENT value from a previously answered 402 (see description)
`amount_usd`	Yes	top-up amount in USD, decimal string

Schema Changelog

Changes observed during successful MCP inspections.

First observedAug 20, 2026

TDQS

A4.6/5.0

Behavior5/5

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

With no annotations provided, the description carries the full burden and does so excellently. It discloses auth requirements, the two-phase 402 challenge flow, the server's inability to sign, and the exact expected x_payment payload structure. This goes well beyond a basic 'top up' statement.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three dense sentences, each earning its place: purpose, auth note, and the two-step payment flow. No filler or repetition; front-loaded with the primary action.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The description covers the complex two-step payment protocol thoroughly, including the 402 response, external signing requirement, and second-call payload. It does not describe the success response or post-payment behavior, but given the complexity and lack of output schema, it is nearly complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3. The description adds meaningful semantics for x_payment by explaining its origin (from a 402 reply) and its internal structure, which is not fully captured in the schema. amount_usd is adequately described by both schema and description.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Top up the prepaid balance with USDC.' This clearly distinguishes the tool from siblings like get_balance or set_auto_topup, and the payment-flow detail reinforces its unique purpose.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear, step-by-step usage instructions: call without x_payment, receive a 402 with EIP-3009 requirements, sign externally, then call again with x_payment. It does not explicitly discuss alternatives or when-not-to-use, but the context is strong enough to guide correct invocation.

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

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