AgentPay-mcp

x402_pay

Fetch URLs requiring payment by automatically handling HTTP 402 responses using the x402 protocol. Pays with your Agent Wallet or reuses existing sessions to avoid repeated on-chain costs.

Instructions

Fetch a URL and automatically handle HTTP 402 Payment Required responses. If an active x402 V2 session covers this URL, the session token is used instead of making a new payment (no on-chain cost). If no session exists, the Agent Wallet pays the required amount and retries. Payment is rejected if it exceeds your wallet's spend limits or the max_payment_eth cap. Powered by the x402 protocol on Base network. Tip: Use x402_session_start to pay once for a session and save on repeated calls.

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": {
      "url": "<url>"
    },
    "name": "x402_pay"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	URL to fetch (HTTP 402 responses are handled automatically)
`method`	No	HTTP method (default: GET)	GET
`headers`	No	Additional request headers
`body`	No	Request body string (for POST/PUT/PATCH)
`max_payment_eth`	No	Maximum payment cap in ETH (e.g. "0.001")
`timeout_ms`	No	Timeout in milliseconds (default: 30000)
`skip_session_check`	No	Skip session auto-detection and force a fresh x402 payment

Schema Changelog

Changes observed during successful MCP inspections.

First observedv3.0.1Mar 20, 2026

TDQS

A4.4/5.0

Behavior4/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes key behaviors: automatic handling of HTTP 402 responses, session token usage to avoid costs, payment rejection based on spend limits or max_payment_eth cap, and the underlying x402 protocol on Base network. However, it lacks details on error handling or response formats, leaving some gaps.

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?

The description is appropriately sized and front-loaded, with the core functionality stated first. Each sentence adds value: explaining session handling, payment logic, rejection conditions, protocol details, and a usage tip. There is no wasted text, making it efficient and well-structured.

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?

Given the tool's complexity (payment handling, session management) and no annotations or output schema, the description is largely complete. It covers the main behavioral aspects and usage context. However, it could benefit from more details on error scenarios or response formats to achieve full completeness.

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

Parameters3/5

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

The schema description coverage is 100%, so the schema already documents all 7 parameters thoroughly. The description adds minimal parameter semantics beyond the schema, such as implying 'url' is the target for payment handling and 'max_payment_eth' sets a cap. Baseline 3 is appropriate as the schema does the heavy lifting.

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 clearly states the tool's purpose: fetching a URL while automatically handling HTTP 402 Payment Required responses. It specifies the verb ('fetch') and resource ('URL'), and distinguishes it from siblings by mentioning the x402 protocol and session handling capabilities, unlike generic payment or session tools in the sibling list.

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

Usage Guidelines5/5

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

The description provides explicit guidance on when to use this tool vs alternatives. It states to use 'x402_session_start to pay once for a session and save on repeated calls,' indicating an alternative for cost-saving scenarios. It also implies usage for URLs requiring payment, with no misleading suggestions.

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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