Damn Vulnerable MCP Server (DVMCP)

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fin.process_payment

Process invoice payments using credit card, ACH, or wire transfer. Enter invoice ID, payment method, and amount to complete the transaction.

Instructions

Process a payment for a specific invoice. Supports credit card, ACH, and wire transfer payment methods.

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": {
      "invoice_id": "<invoice_id>",
      "method": "<method>",
      "amount": "<amount>"
    },
    "name": "fin.process_payment"
  }
}

Input Schema

Name	Required	Description
`invoice_id`	Yes	Invoice ID to process payment for
`method`	Yes	Payment method
`amount`	Yes	Payment amount

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.0.0Jun 22, 2026

TDQS

C2.9/5.0

Behavior2/5

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

No annotations are provided, so the description carries the full burden. It says 'Process a payment' but does not disclose consequences, reversibility, required permissions, or side effects. For a financial mutation, this is a significant gap.

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 a single, front-loaded sentence with no redundant words. It efficiently states the action and supported methods.

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

Completeness2/5

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

This is a mutational and financially sensitive tool with no output schema or annotations. The description omits crucial context such as return values, error handling, and side effects, leaving the agent underinformed for a high-stakes operation.

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?

Schema description coverage is 100%, so parameters are already documented. The description repeats the payment methods enum but adds no additional meaning beyond what the schema provides.

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?

The description clearly states the tool processes a payment for a specific invoice and lists supported methods (credit card, ACH, wire). However, it does not differentiate from the sibling tool fin.wire_transfer, which could also be used for wire payments.

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

Usage Guidelines2/5

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

No explicit guidance on when to use this tool versus alternatives like fin.wire_transfer or fin.query_invoices. It does not mention prerequisites (e.g., invoice must exist) or scenarios where another tool would be more appropriate.

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