presign-guard

A pre-sign risk check for AI agents. Before an agent signs a transaction, approval, or EIP-712 signature, it pays a few cents per call over x402 and gets back a green / orange / red verdict with machine-readable reason codes. Optionally, it also gets a plain-language explanation in Dutch or English.

Watch the 1-minute explainer: presign-guard.fizzl.eu/media/explainer.mp4

New: the token verdict in 45 seconds: presign-guard.fizzl.eu/media/token.mp4

Part of Klaartaal by FIZZL AI.

Endpoints

Payment is x402 v2 with the exact scheme, in USDC on Base (the token verdict and the approval audit also on Solana). The 402 carries Bazaar discovery metadata (input example, input and output schema), and the challenge is mirrored into the JSON body for clients that don't read the PAYMENT-REQUIRED header. You are never charged for an error. Invalid requests (400) and upstream outages (503) cancel settlement, and they always return verdict: null, never a guessed verdict.

MCP

https://presign-guard.fizzl.eu/mcp is an MCP server (Streamable HTTP, stateless) for Claude, Cursor and agent frameworks, listed in the official MCP registry as io.github.Fizzl13/presign-guard.

The paid tools are paid inside the MCP call with the x402 MCP transport (_meta["x402/payment"]), on Base (token_verdict and wallet_approvals also on Solana), to the same payout wallets as the HTTP routes. Invalid input is refused before payment, and a failed check is not charged.

Token verdict

GET /v1/token?chain=solana&address=<mint> (or chain=base|ethereum|arbitrum|optimism|polygon|bsc with a 0x token contract) answers one question before an agent buys, holds or accepts a token: is the token itself a trap?

{
  "verdict": "orange",
  "grade": "RISKY",
  "one_liner": "RISKY: 1% transfer fee; $21k liquidity; 1 h old (+2 more)",
  "reasons": [{ "code": "TRANSFER_FEE", "severity": "orange", "details": { "feePct": 1 } }, "…"],
  "token": { "chain": "solana", "address": "…", "name": "…", "symbol": "…" },
  "market": { "priceUsd": 0.0004, "liquidityUsd": 21000, "marketCapUsd": 400000, "volume24hUsd": 90000, "firstPairAt": "…", "ageSeconds": 3600, "url": "https://dexscreener.com/…" },
  "sources": ["goplus", "dexscreener", "rugcheck"],
  "checkedAt": "…"
}

Grades: SAFE (green), CAUTION (one orange reason), RISKY (two or more), AVOID (red). The one-liner states facts only.

For a proxy token (USDC, cbBTC, EURC on Base) GoPlus reports no pause or blacklist fields, so the verdict asks the token itself with eth_call on the standard getters (paused, pauser, PAUSER_ROLE, blacklister, isBlacklisted, isBlackListed); those reasons carry source: "onchain" and the role address, and sources includes chain. If the chain RPC is down they are left out and the verdict still answers.

On a token on the GoPlus trust list (USDC, USDT), the issuer's powers (mint, freeze, change balances) are info: the issuer keeps them on purpose. Missing data never makes a token red. If GoPlus or DexScreener is down there is no verdict (503, not charged); if RugCheck is down the verdict comes without it and says so.

Wallet approval audit

GET /v1/approvals?chain=base&address=<wallet> (or chain=ethereum|arbitrum|optimism|polygon|bsc) is the follow-up to /v1/check: that one asks "should I sign this approval?", this one asks "which approvals did I already give, and which should I revoke?". Agents with their own wallet can run it as a periodic check.

{
  "verdict": "red",
  "grade": "AVOID",
  "one_liner": "AVOID: 5 approvals, 1 to a flagged address, 1 to a plain wallet, 1 unlimited; revoke 3",
  "reasons": [{ "code": "SPENDER_MALICIOUS", "severity": "red", "details": { "count": 1, "spenders": ["0x…"] } }, "…"],
  "summary": { "approvals": 5, "tokens": 2, "unlimited": 2, "toRevoke": 3 },
  "approvals": [{
    "token": { "address": "0x…", "symbol": "USDC" },
    "spender": { "address": "0x…", "name": null, "trusted": false, "contract": true },
    "amount": "500", "unlimited": false, "approvedAt": "…", "severity": "red",
    "codes": [{ "code": "SPENDER_MALICIOUS", "severity": "red", "details": { "behaviors": ["phishing_activities"] } }],
    "revoke": true
  }, "…"],
  "revokeUrl": "https://revoke.cash/address/0x…?chainId=8453"
}

Every approval with an orange or red code has revoke: true. The grades are the same as the token verdict. Source: GoPlus token_approval_security (ERC-20 allowances); NFT approvals are not covered. If GoPlus is down there is no verdict (503, not charged).

Request types

// Token approval
{ "type": "approval", "chainId": 8453, "token": "0x…", "spender": "0x…", "amount": "1000000" }

// Raw transaction (approve / increaseAllowance / setApprovalForAll are decoded)
{ "type": "transaction", "chainId": 8453, "to": "0x…", "data": "0x…", "value": "0" }

// EIP-712 signature: pass the eth_signTypedData_v4 payload as an object or JSON string
{ "type": "signature", "chainId": 8453, "typedData": { "domain": {…}, "types": {…}, "primaryType": "PermitSingle", "message": {…} } }

Supported chains: 1, 10, 56, 137, 8453, 42161.