Blackwall X402 Guardrail

com.blackwalltierPublished by blackwalltier.comOfficial publisherv0.1.2Updated Oct 24, 2026

Keyless hosted MCP: pre-signature x402 payment verdict (GO/HOLD/STOP) with a signed receipt.

VerifiedStreamable HTTPWeb executableFinanceSecurity & Monitoring

Overview

AI-generated overview

Hosted remote MCP that gives an agent a pre-signature GO/HOLD/STOP risk verdict, with a signed receipt, before it pays an x402 counterparty.

What you can do
  • Request a payment verdict for a counterparty wallet, amount, asset and chain, with optional payer, resource, agent ID and context fields.
  • Get GO, HOLD or STOP plus reasons and signals based on settlement reputation, price anomaly against the payee's own median, and OFAC sanctions.
  • Receive an Ed25519 signed receipt that a third party can verify independently against a published key.
When to use it
Use it when an agent is about to sign an x402 payment and you want a second opinion on whether the counterparty and price look safe. It suits automated payment flows that need a checkable audit trail rather than custody or settlement.
Requirements
A remote Streamable HTTP endpoint; no install, signup or API key. Calls need counterparty, amount, asset and chain. Verdicts for amounts under $10 at risk are free; at or above that the tool returns an x402 payment challenge that the agent must settle from its own wallet and return as an X-PAYMENT header before retrying.
Before you install
Above the free threshold the agent must pay from its own wallet to get a verdict, so spending is involved. The tool only returns a verdict and never takes custody, but a GO is not a guarantee. Calls are forwarded to a separate oracle service, and the receipt key is published at a different host, so availability of both matters; failures return an error rather than a GO.

Installation

In SourceWeft

  1. Open Blackwall X402 Guardrail in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via Streamable HTTP. Remote servers run from the web runtime once configured in a workspace.

Use with an agent

Paste this prompt into Claude Code, Codex, Cursor or another agent — or into SourceWeft chat. The agent reads this server's install guide, shows you its publisher, endpoint and sign-in, and adds it to your client once you agree. Keys never go into a command.

Read https://sourceweft.com/mcp/com.blackwalltier%2Fblackwall-x402-guardrail/install.md and connect the MCP server it describes to my client. Before changing any config, show me its publisher, endpoint and sign-in method and wait for my OK. Never put an API key in a command or in a file I would commit; ask me where it should come from.

Read the install guide the agent follows

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "blackwall-x402-guardrail": {
      "type": "http",
      "url": "https://mcp.blackwalltier.com/"
    }
  }
}

README

Black_Wall remote MCP

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
counterpartystring, requiredrecipient wallet from the 402
amountstring, requireddecimal string, e.g. "0.09"
assetstring, requirede.g. USDC
chainstring, requirede.g. base
payer / resource / agent_id / contextoptionalbinds 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

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

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

Source: README.md at commit 4a69626

Tools

1

forecast_payment

Pre-signature x402 payment verdict: GO / HOLD / STOP for paying a counterparty, from settlement reputation, price-anomaly (quoted vs the payee's own median), and OFAC sanctions — with a third-party-verifiable Ed25519 signed receipt. Verdict only; never takes custody. Free under $10 at risk; over that, returns an x402 payment challenge.

Parametersassetrequiredchainrequiredpayeramountrequiredcontextagent_idresourcecounterpartyrequired

Version history

1
  1. v0.1.2LatestSep 16, 2026

Score

90% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

  • Reached in the last 30 daysRequired25 pts
  • Auth declaredRequired10 pts
  • Tools listedRequired15 pts
  • DescriptionRequired15 pts
  • Logo10 pts
  • Documentation15 pts
  • License10 pts

    Declare a license in the repository or the registry entry.

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