Solana X402 Compliance

x402 MCP Server

A lightweight, zero-bloat Model Context Protocol (MCP) server that exposes the Solana Enterprise Payment Gateway's POST /api/v1/compliance/screen-address endpoint as an autonomous tool for AI agents (Claude Desktop, Cursor, VS Code Cline, ElizaOS).

The agent transparently negotiates and settles the x402 micro-payment on every screen: it receives the HTTP 402 Payment Required challenge, signs an Ed25519 channel voucher in-memory (Node.js built-in crypto, no Web3 SDK), and retries with a PAYMENT-SIGNATURE header.

Standalone npm package

The server is published to the npm registry as a standalone package — no clone or build step is required to run it:

npx -y @msantagiulianab/x402-mcp-server

See package.json for the current version and metadata. The package ships the compiled ESM dist/ bundle plus this README and the LICENSE.

Layout

agent-tools/mcp-server/├── src/│   ├── base58.ts          # zero-dependency Base58 codec│   ├── ed25519.ts         # Node crypto Ed25519 keypair + canonical payload│   ├── x402-client.ts     # autonomous X402Client (402 -> sign -> retry)│   └── index.ts           # MCP server + tool registration├── test/                  # offline unit + stdio integration tests├── test-agent-call.js     # live verification against the running Docker stack├── package.json├── smithery.yaml          # Smithery registry manifest└── tsconfig.json

Install & build

cd agent-tools/mcp-servernpm installnpm run build          # tsc -> dist/ (ESM)

Run (stdio transport)

npx -y @msantagiulianab/x402-mcp-server   # published package# or, from a local checkout:npm start# or: node dist/index.js

Environment variables:

X402_GATEWAY_URL and X402_CHANNEL_ID are injected by the MCP host (Claude Desktop, Cline, Smithery, etc.); X402_PRIVATE_KEY_SEED is optional and defaults to the deterministic smoke-test payer.

The tool screen_solana_address:

• Description: Inspect a Solana address against sanctions and threat intelligence databases. Automatically negotiates and settles micro-payments via x402.
• Input: address — a valid Base58 Solana public key (decodes to 32 bytes).
• Output: formatted JSON text containing verdict, riskScore, flags, and the evaluation timestamp.

The tool get_channel_status:

• Description: Retrieve current operational status, limits, and settlement state of a given x402 payment channel.
• Input: channel_id — the unique identifier of the payment channel.
• Output: formatted JSON text containing status ("ACTIVE"), currency ("USDC"), network ("solana-devnet"), capacity ("10000.00"), and lastSettlementBlock.

The tool generate_compliance_report:

• Description: Generate an immutable audit summary report for a Solana wallet address or transaction signature against sanctions and threat intelligence logs.
• Input: identifier — a Solana wallet address (32-byte Base58) or a transaction signature (64-byte Base58).
• Output: formatted JSON text containing complianceStatus ("PASSED" | "FLAGGED" | "UNSCREENED"), riskScore (a number for screened identifiers, null when unscreened), flags, sanctionsMatch, checkedLists ([] when unscreened, otherwise ["OFAC", "EU_SANCTIONS", "CHAIN_REPUTATION"]), lastEvaluated, evaluationTimestamp, timestamp, and reportId. The report fails closed: it references the session's in-memory screening ledger and returns "UNSCREENED" until the identifier has been live-screened via screen_solana_address.

Architecture & Sync Workflow

This component is one of three independently deployable surfaces in the repository. Changes flow differently depending on where they live:

The backend and the MCP server deploy independently: a Java change does not require an npm publish, and an MCP change does not require a VPS reload. Documentation and registry metadata (smithery.yaml) ship purely via GitHub.

smithery.yaml

smithery.yaml is the Smithery registry manifest. It declares the stdio startCommand (npx -y @msantagiulianab/x402-mcp-server) and exposes two configurable fields — gatewayUrl and channelId — which map onto the X402_GATEWAY_URL and X402_CHANNEL_ID environment variables. Updating it only requires a GitHub push; the Smithery registry indexes it directly from the repository.

Tests

npm test

This compiles the project and runs:

• base58.test.js — Base58 codec round-trips and 32-byte address validation.
• ed25519.test.js — golden-vector check that the canonical payload and Ed25519 signature exactly match smoke-test.sh / the JVM PaymentVoucher layout.
• x402-client.test.js — full 402→sign→retry negotiation against a mock gateway, with independent Ed25519 signature verification of the emitted voucher.
• mcp-server.test.js — spawns the real server and drives it with an MCP client over stdio (list tools + call screen_solana_address).

Live verification against the running stack

With the Docker stack up (docker compose up -d --build):

npm run test:tool

This exercises the tool handler against http://localhost:8080:

• Clean address 4Nd1mBQtrMJVYVfKf2PJy9NZGibCcTRxpETqdrBHu19Y → CLEAR_TO_TRANSACT.
• Flagged address Fc1EwQUZyTEagaDvA1utHXCcZNyG1x2PLt2DfNu1cJdH → BLOCKED.

Client configuration

Claude Desktop

Add to claude_desktop_config.json:

macOS / Linux

{  "mcpServers": {    "solana-x402-compliance": {      "command": "npx",      "args": ["-y", "@msantagiulianab/x402-mcp-server"],      "env": {        "X402_GATEWAY_URL": "https://msb-solana-enterprise-payment-gateway.duckdns.org",        "X402_CHANNEL_ID": "chan_smoke_test_001"      }    }  }}

Windows

{  "mcpServers": {    "solana-x402-compliance": {      "command": "cmd",      "args": ["/c", "npx", "-y", "@msantagiulianab/x402-mcp-server"],      "env": {        "X402_GATEWAY_URL": "https://msb-solana-enterprise-payment-gateway.duckdns.org",        "X402_CHANNEL_ID": "chan_smoke_test_001"      }    }  }}

VS Code Cline

Add to cline_mcp_settings.json:

{  "mcpServers": {    "solana-x402-compliance": {      "command": "npx",      "args": ["-y", "@msantagiulianab/x402-mcp-server"],      "env": {        "X402_GATEWAY_URL": "https://msb-solana-enterprise-payment-gateway.duckdns.org",        "X402_CHANNEL_ID": "chan_smoke_test_001"      }    }  }}

Cursor

Add an MCP server entry (Settings → MCP) pointing at the same npx -y @msantagiulianab/x402-mcp-server command with the environment variables above.

ElizaOS

Register a stdio-based MCP client plugin using the same npx -y @msantagiulianab/x402-mcp-server command; the tool screen_solana_address becomes callable by the agent.