MCP · stdio · free gate
One MCP server gives Claude Desktop, Cursor, OpenCode, or any agent the free preflight gate plus five paid on-chain checks. The free gate answers with a receipt; the paid checks settle per call over x402.
Official MCP Registry: active npm: verify402-mcp v1.0.3 Free gate · no wallet
The tool surface
The gate is free because it has to run before every signature. The paid tools answer the questions that need a measurement at a pinned block.
| Tool | Price | Question | What comes back |
|---|---|---|---|
| preflight_gate | free | Should I sign this payment or transaction? | PASS / CAUTION / BLOCK, typed reasons, checked / notChecked, and a short-lived receipt |
| verify_arbitrage | $0.05 | Is this cross-venue arbitrage real, right now? | Verdict + evidence + no_edge when there is none |
| check_token_safety | $0.10 | Is this token safe to buy? | TRUST / CAUTION / AVOID, live contract facts, liquidity, a sell probe |
| get_best_route | $0.03 | What would the chain actually pay? | Every quoted venue at one pinned block, best first |
| verify_quote_fairness | $0.05 | Is this quote someone gave me honest? | fair / overpaying / too_good_to_be_true, with the chain book |
| get_trade_depth | $0.05 | How big can I trade before the round trip eats me? | Per-size impact, round-trip cost, and the largest size under your tolerance |
Paid calls are USDC over x402. The bridge signs the payment only — it never signs or sends a trade — and it only pays a 402 from the configured server, on an allowlisted network, to the verify402 payee.
Install
Published to the public npm registry and the official Model Context Protocol Registry. Run directly with npx without cloning or building.
Mode 1 · no key
Omit EVM_PRIVATE_KEY. The server registers only preflight_gate, logs free preflight_gate only, and nothing can be charged. This is the safest way to try it.
Mode 2 · paid tools
Add a wallet with USDC on the payment network. MAX_PAYMENT_USD caps one payment at signature time; MAX_DAILY_USD caps the UTC day. Never use a main wallet.
Run via npx · no wallet required
npx -y verify402-mcp --help
Published on npm as verify402-mcp (version 1.0.3) and listed on the official Model Context Protocol Registry as io.github.a32116150-ctrl/verify402-mcp. Machine agents can also fetch the machine-readable service manifest and OpenAPI 3.1 specification.
Client · Claude Desktop / Cursor
Claude Desktop uses claude_desktop_config.json; Cursor uses .cursor/mcp.json. This block is free-only. For paid tools, add EVM_PRIVATE_KEY, MAX_PAYMENT_USD and optionally MAX_DAILY_USD to env.
Free-only config
{
"mcpServers": {
"verify402": {
"command": "npx",
"args": [
"-y",
"verify402-mcp"
],
"env": {
"VERIFY402_URL": "https://verify402.onrender.com"
}
}
}
}
Client · OpenCode V2
Put this in opencode.jsonc or the global ~/.config/opencode/opencode.jsonc. For paid tools, use "EVM_PRIVATE_KEY": "{env:EVM_PRIVATE_KEY}" and export the key in the environment that starts OpenCode — do not write it into the file.
opencode.jsonc · free-only
{
"$schema": "https://opencode.ai/config.json",
"mcp": {
"servers": {
"verify402": {
"type": "local",
"command": [
"npx",
"-y",
"verify402-mcp"
],
"environment": {
"VERIFY402_URL": "https://verify402.onrender.com"
}
}
}
}
}
V2 uses mcp.servers and disabled; there is no enabled field. The server name prefixes its tools in OpenCode.
If you prefer a pinned release tarball: npx -y --package=https://github.com/a32116150-ctrl/verify402/releases/download/mcp-v1.0.3/verify402-mcp-1.0.3.tgz verify402-mcp. From source: git clone https://github.com/a32116150-ctrl/verify402, then cd verify402/mcp-bridge && npm ci.
The honesty boundary
| It checks | It does not |
|---|---|
| A swapped payee, a lookalike asset, a wrong amount, a bad network, an expired authorization | Whether the recipient is a scammer or a sanctioned address |
| Decoded calldata: transfers, approvals, permits, common V2/V3 swaps; unlimited approvals and spenders | Contract audits, proxy upgrades, owner privileges, or a token's intent |
Contract bytecode, swap deadline, minimum output, output recipient, and an eth_call simulation from your wallet | Full balance-delta / state-change simulation; MEV and sandwich protection |
| The x402 payment itself: price, network, asset, payee, facilitator, before the caller signs | Counterparty identity, tool metadata, hidden instructions in tool output, or off-chain promises: “the seller will deliver after you pay” |
| Receipt integrity: HMAC, intent hash, pinned block, expiry | The agent ignoring the tool, or a signer that does not verify the receipt |
A PASS means the left column passed at that block. It is not a guarantee that a token is safe, a trade will profit, or a counterparty will deliver. It is not a counterparty audit and does not scan tool descriptions or responses for prompt injection. It catches a class of measurable signing mistakes — not every scam.
The MCP tool is advisory: it cannot stop an agent that ignores the answer. Use the reference executor to verify the receipt and refuse to call the signer without it. The full request shape is in /docs#preflight.
Why a package
An MCP server is only in the path if installing it is one line. npx runs a versioned package on first use, your client config stays small, and updates are a version bump — not a git pull. The package is distribution, not another endpoint.
01
One block in Claude, Cursor, or OpenCode. No build, no clone, no submodule.
02
Free, no wallet. The agent gets PASS / CAUTION / BLOCK and a receipt bound to the intent and block.
03
When the agent needs a measurement, the same server pays per call over x402. No subscription.
Install from the public npm registry with npx -y verify402-mcp@latest; the versioned GitHub release tarball above is an optional fallback. Package name: verify402-mcp. License: Apache-2.0 — keep the copyright notice, license, and NOTICE file when redistributing. Source: mcp-bridge.