Blackwall X402 Guardrail

A hosted remote MCP (Model Context Protocol over HTTP) that gives any MCP-capable agent a pre-signature payment-risk verdict — with no install and no signup. Add one URL and your agent can ask, before it signs an x402 payment, "should I pay this?" and get GO / HOLD / STOP — from counterparty settlement reputation, price-anomaly (quoted vs the payee's own median), and OFAC sanctions — plus a third-party-verifiable Ed25519 signed receipt.

Add it

Point your MCP client at:

https://mcp.blackwalltier.com

Transport: Streamable HTTP. No API key. Verdicts for amounts under $10 at risk are free; at or above that, the tool returns an x402 payment challenge your agent settles from its own wallet (pass the settled payment back as an X-PAYMENT header, then retry).

The tool: forecast_payment

field
counterparty	string, required	recipient wallet from the 402
amount	string, required	decimal string, e.g. "0.09"
asset	string, required	e.g. USDC
chain	string, required	e.g. base
payer / resource / agent_id / context	optional	binds settlement / context

Returns a verdict (GO/HOLD/STOP) + reasons + signals, and a signed_receipt anyone can verify against the published key at https://agent-egress-proxy.onrender.com/.well-known/blackwall-receipt-key.json (any RFC 8032 Ed25519 library) — Black_Wall never has to be in the loop.

How it works

This Worker is a thin transport + proxy: it speaks minimal MCP JSON-RPC (initialize / tools/list / tools/call / ping) and forwards forecast_payment calls to the Black_Wall x402 oracle. All decision logic and the receipt come from the oracle unchanged.

Fail-closed by design: if the oracle errors, is unreachable, or returns a non-verdict, the tool returns an error — never a phantom GO. A payment guardrail that can't reach its backend must not imply "safe to pay."

Registry

Published to the official MCP Registry as com.blackwalltier/blackwall-x402-guardrail.

Develop

node test.mjs        # unit tests (mocked oracle)
npx wrangler dev     # run locally
npx wrangler deploy  # deploy (Cloudflare Workers)

By BlueTier. Verdict only — never takes custody, never in the settlement path. No evidence is not trust.