scdo-agent-plugins

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Pay x402 resource

pay_x402

Pay HTTP 402 resources from an agent wallet with EIP-3009 authorization, gas paid by the facilitator. Preview price and keep within maxUsdc and caps.

Instructions

Pay an HTTP 402 (x402) resource from the agent wallet with an EIP-3009 authorization. The facilitator pays gas. The price is previewed first and must be within maxUsdc and the caps.

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": {
      "bot": "<bot>",
      "url": "<url>"
    },
    "name": "pay_x402"
  }
}

Input Schema

Name	Required	Description	Default
`bot`	Yes
`url`	Yes
`maxUsdc`	No
`network`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 20, 2026

TDQS

A3.5/5.0

Behavior4/5

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

With no annotations, the description carries real weight: it discloses that gas is borne by the facilitator, that payment uses an EIP-3009 authorization, and that spend is bounded by maxUsdc and caps (i.e., the call can be rejected on price). It omits the irreversible nature of the spend and error/failure behavior, keeping it from a 5.

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 short sentences, front-loaded with the action and mechanism, then the cost/gas detail, then the cap constraint. Every sentence earns its place with no filler.

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

Completeness3/5

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

For a payment tool with no annotations and no output schema, the description adequately covers the mechanism and spend constraints, and the absent output schema means return values need not be explained. However, it leaves three of four parameters undefined and says nothing about failure/rollback behavior, so it is only minimally sufficient.

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

Parameters2/5

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

Schema coverage is 0%, so the description must document all four parameters, but it only gives meaning to maxUsdc (a spending ceiling the previewed price must fall within). The required 'bot' and 'url' and the 'network' enum (base/base-sepolia) are left entirely unexplained.

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

Purpose4/5

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

States a specific verb and resource ('Pay an HTTP 402 (x402) resource from the agent wallet') and adds the mechanism (EIP-3009 authorization), which clearly separates it from read-only x402 siblings like x402_catalog and x402_quote. It stops short of naming those siblings to actively differentiate, so it lands at 4 rather than 5.

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

Usage Guidelines3/5

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

'The price is previewed first' implies a two-step quote-then-pay flow, which is usable context, but it never names x402_quote explicitly nor states when not to call this tool or what preconditions (wallet funded, prior quote) must hold. Usage is implied rather than spelled out.

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