Hermes Plant

Payment Policy — preflight an x402 payment

payment_policy_decide

Idempotent

Payment Policy Decision (x402-paid, $0.05): deterministic allow / deny / needs_review before your agent signs an x402 payment — checks resource binding, amount vs expected price, network, payTo, facilitator, replay readiness, PII leakage, and buyer spend limits, with evidence-backed findings. Loop it over every payment; pair with assurance_attest for a signed record.

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": {
      "resourceUrl": "<resourceUrl>"
    },
    "name": "payment_policy_decide"
  }
}

Input Schema

Name	Required	Description
`tags`	No	Bazaar/service tags for sensitive-category detection
`asset`	No	Payment asset address
`payTo`	No	Payment recipient from the challenge
`payer`	No	Optional wallet/account identifier; stored only as a hash
`apiKey`	No	Free-tier / plan API key (hp_free_… or a pass key). Forwarded as X-API-Key so paid tools serve from your monthly quota with NO x402 wallet. Get a free key (250 calls/mo) at https://hermesplant.com/pricing.
`method`	No	HTTP method the agent intends to call
`scheme`	No	x402 payment scheme (exact expected)
`channel`	No	Discovery channel or source tag
`network`	No	Payment network, e.g. eip155:8453
`campaign`	No	Campaign tag for downstream telemetry
`xPayment`	No	Raw X-PAYMENT proof from an x402-compatible wallet/client
`actorType`	No	Caller type for analytics: agent, human, synthetic, system, or unknown
`synthetic`	No	Mark this paid retry as an internal test/probe for analytics exclusion
`amountUnits`	No	Raw x402 amount units (USDC = 6 decimals)
`buyerPolicy`	No	Buyer guardrails: maxUsdPerCall, allowedNetworks, allowedPayTo, allowedHosts, requireExactScheme, requireHttps, ...
`resourceUrl`	Yes	Absolute resource URL from the x402 challenge or Bazaar listing
`serviceRisk`	No	Optional upstream service-risk result (e.g. from mcp_risk_score)
`facilitatorUrl`	No	Facilitator URL used to settle
`paymentSignature`	No	x402 payment proof to forward as PAYMENT-SIGNATURE and X-PAYMENT on retry
`maxTimeoutSeconds`	No	Challenge timeout window
`paymentIdentifier`	No	Optional x402 payment identifier for idempotency/retry correlation

Output Schema

Name	Required	Description
`ok`	Yes	True when the upstream storefront call returned a 2xx response
`httpStatus`	Yes	Upstream HTTP status code
`paymentRequired`	No	True when the response is an x402 HTTP 402 payment challenge

Schema Changelog

Changes observed during successful MCP inspections.

AddedJul 13, 2026

TDQS

A4.7/5.0

Behavior5/5

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

The description discloses cost ($0.05), determinism, and the specific checks (resource binding, replay readiness, PII leakage, spend limits) which go beyond the annotations (idempotent, non-destructive). This adds substantial behavioral context without contradicting any annotation.

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 sentences with the tool name and cost front-loaded, followed by the action and key checks. No filler or redundancy; every sentence adds value.

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

Completeness5/5

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

For a tool with 21 parameters, nested objects, and an output schema, the description adequately covers the decision outcome, cost, usage context, and relationship to sibling tools. The output schema handles return values, so no relevant gap remains.

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 baseline is 3. The description adds meaning by linking the checks to parameter categories (network, payTo, facilitator, buyerPolicy, etc.), which helps agents map inputs to decision logic.

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 uses a specific verb ('preflight'/'decide') and resource ('x402 payment'), explicitly stating the outcome (allow/deny/needs_review) and listing the checks performed. It distinguishes itself from siblings like assurance_attest by clarifying its preflight role.

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 instruction 'Loop it over every payment' provides explicit when-to-use guidance, and 'pair with assurance_attest for a signed record' names a complementary tool. However, it lacks explicit when-not-to-use conditions or alternatives.

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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