Blackwall X402 Guardrail
Pre-signature x402 payment verdict (GO/HOLD/STOP) for AI agents, with a verifiable signed receipt.
Install Blackwall X402 Guardrail
Pick your client, then add it in one click or paste the config.
https://mcp.blackwalltier.com
Remote servers are added in the app, not the config file: Customize → Connectors → Add custom connector, then paste this URL.
Overview
From the project README
Security & health
What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.
ActiveLast checked 4d ago
Recent health check succeeded.
19/19 checks healthy over the last 67d
Supply-chain signal
2 high-severity advisories on record for this package. Most advisories affect transitive dependencies and may not be exploitable in this server's actual usage — this is a directional signal, not a security audit.
Critical 1High 1Medium 2Low 0
Scanned 8/17/2026 via OSV.dev · https://mcp.blackwalltier.com (npm)
Adoption & maintenance
Factual signals from GitHub, npm, and our automated checks — not a rating.
Last commit1mo agoMost recent push to the default branch.
Directory activity1 viewsConfig copies, upvotes, and views on AllMCPs.
Reviews
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Frequently Asked Questions about Blackwall X402 Guardrail
blackwall-x402-guardrail is an MCP server that provides pre-signature x402 payment-risk verdicts for AI agents. Before an agent signs a payment, it evaluates counterparty settlement reputation, quoted-price anomalies, and OFAC sanctions, returning GO, HOLD, or STOP with a third-party-verifiable Ed25519 signed receipt. It runs remotely over Streamable HTTP, requiring no install or signup.
Connect an MCP client to https://mcp.blackwalltier.com using the Streamable HTTP transport. No API key or signup is required. The server supports the MCP operations initialize, tools/list, tools/call, and ping.
The server provides the forecast_payment tool for checking an x402 payment before signing it. Required inputs are counterparty, amount as a decimal string, asset, and chain; payer, resource, agent_id, and context are optional. The tool returns a GO, HOLD, or STOP verdict with reasons, signals, and a signed receipt.
Verdicts for amounts under $10 at risk are free. For amounts at or above $10 at risk, the tool returns an x402 payment challenge that the agent settles from its own wallet, then retries with the settled payment in the X-PAYMENT header.
Verify the signed_receipt independently using an RFC 8032 Ed25519 library and the published key at https://agent-egress-proxy.onrender.com/.well-known/blackwall-receipt-key.json. Black_Wall does not need to remain in the verification loop.
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