x402 + MCP validation

The sentinel endpoint is a paid MCP service. It returns x402 payment requirements to unpaid callers and accepts a signed X-PAYMENT header from paid callers.

Endpoint

https://prism-sentinel-production.up.railway.app/mcp/

The trailing slash is part of the canonical endpoint.

Trust tools

Prism exposes the sentinel as an MCP trust plug-in, not only as a dashboard action. External agents can call:

Tool	Purpose
`validate`	Pay for an adversarial verdict on a Trading-R1 trace pinned to IPFS.
`verify_receipt`	Check a pinned verdict receipt against content-hash and DB anchors.
`get_issue_ledger`	Inspect unresolved blocking/material issues for a persisted validation.
`explain_verdict`	Return a deterministic explanation of the verdict and active gates.
`get_tool_manifest`	Inspect redacted connector/tool capabilities without exposing secrets.
`get_price`	Read current validation price and settlement network.
`get_stats`	Read aggregate sentinel statistics.
`get_calibration`	Read calibration evidence for sentinel discrimination.

The point is operational: another trading agent can validate a trace, inspect unresolved issues, verify receipts, and decide whether capital is allowed to continue before it trades.

Flow

Initialize the MCP session.
Call the validation tool without payment to receive x402 requirements.
Sign the EIP-712 authorization externally or through Circle CLI.
Retry the same MCP tool call with X-PAYMENT.
Persist the returned verdict and receipt fields.

The CLI wraps this flow:

uv run prism quote ipfs://Qm... --trace-hash 0x...
uv run prism validate ipfs://Qm... --trace-hash 0x... \
  --circle-address 0xYOUR_BASE_SEPOLIA_WALLET \
  --max-amount-usdc 0.01

Payment safety

Prism CLI enforces three boundaries:

no raw private keys
explicit --pay or validate command before payment
a caller-provided max payment cap

The Circle CLI command is executed as a subprocess with shell=False. Prism passes typed-data input to Circle CLI and receives a signed payment payload; the private key remains inside Circle's wallet boundary.

MCP versus REST

The sentinel endpoint is MCP JSON-RPC/SSE. Do not model /mcp/ as a normal REST endpoint in OpenAPI. The dashboard public APIs are REST; the sentinel validation service is MCP.

Example quote data

A quote includes fields like:

{
  "amount_usdc": "0.01",
  "amount_units": "10000",
  "asset": "USDC",
  "network": "base-sepolia",
  "caip2": "eip155:84532",
  "scheme": "exact"
}

Always compare amount_usdc to your configured payment cap before signing.