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Blackwall X402 Guardrail MCP server

online · 100% uptime
by blackwalltier.com·com.blackwalltier/blackwall-x402-guardrail·v0.1.2
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Keyless hosted MCP: pre-signature x402 payment verdict (GO/HOLD/STOP) with a signed receipt.

A87/100grade A
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Safety scan
A87/100

full report

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If you have run it, two minutes of your experience saves the next person an afternoon.

Blackwall X402 Guardrail tools (1)

write = sends, deletes, buys or posts
  • forecast_paymentFree

    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.

Public scan report

scanner v0.1.10 · 2026-10-31 · same rubric, same numbers if you re-run it

no findings
  • –Code scanremote-only server, no package to scann/a
  • Live reliabilityremote reachable in 293ms20/20
  • Tool poisoning1 tool descriptions checked15/15
  • Auth qualityopen endpoint, read-only tools10/15
  • Maintenancelast push 68 days ago12/15
  • Maintainer identityendpoint served from the registry-verified namespace domain8/10
Overall 87/100. Components that don't apply are left out of the denominator. Any critical finding is an F.RubricAppeal a findingJSON

How Blackwall X402 Guardrail compares

Against every graded Finance MCP server, from our own scans and uptime checks. Updated after each scan run.

Safety score
87/100
higher than 83% of 1,759 Finance servers
Tools
1
the typical Finance server has 8
Tools that change things
0%
typical: 0%. Fewer write tools means less an agent can break
Uptime
100%
of our recent checks; the typical remote Finance server answers 100%
Response time
76 ms
faster than 91% of 1,131 Finance servers

What its tools let an agent do: 1 read

Install Blackwall X402 Guardrail in Claude Code, Cursor or VS Code

claude mcp add --transport http blackwall-x402-guardrail https://mcp.blackwalltier.com
Add to Cursor

What the publisher says

From the Blackwall X402 Guardrail repository's README, as published. We do not edit it. Read it on GitHub

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

Returns a verdict (GO/HOLD/STOP) + reasons + signals, and a signedreceipt 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) — BlackWall 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 forecastpayment calls to the BlackWall 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.

Nothing above is checked by us. What we check is on the safety report.

Blackwall X402 Guardrail: common questions

Is Blackwall X402 Guardrail MCP server safe?
Yes, by our scan: it is graded A (87/100). Read the Blackwall X402 Guardrail safety report
How do I install Blackwall X402 Guardrail?
It runs remotely at mcp.blackwalltier.com. Add it to Claude Code, Cursor, VS Code or Claude Desktop with the snippets above, or call it through the mcp.market gateway without installing anything.
Does Blackwall X402 Guardrail need an API key?
Not as far as the registry entry and our scan can tell: no credentials are declared or required.
Is Blackwall X402 Guardrail maintained?
The last commit was 72 days ago (2026-08-25). The latest release is v0.1.2.
Is Blackwall X402 Guardrail up?
100% of our last 28 checks got an answer. We check remote servers about four times a day.
What can I use instead of Blackwall X402 Guardrail?
Servers from other publishers that do the same job: Kenwea — Sandbox Attestation & Agent Marketplace MCP server, three.ws Agent Payments MCP server and X402 List MCP server.
How does Blackwall X402 Guardrail compare with other Finance MCP servers?
safety score 87/100 (higher than 83% of 1,759 Finance servers); tools 1 (the typical Finance server has 8); tools that change things 0% (typical: 0%. Fewer write tools means less an agent can break). Full comparison.

Alternatives to Blackwall X402 Guardrail

Same job from other publishers: the closest match first, then the best rated.