presign-guard wallet

presign-guard-wallet-mcp

A wallet with spending limits for AI agents, as an MCP server. Add it to Claude Desktop, Claude Code, Cursor or any other MCP client, and your agent can:

• pay for x402 APIs, and MPP APIs: method evm (USDC on the wallet's chain) and method tempo (USDC.e on Tempo, what nearly every MPP API asks for);
• with its own accounts there, also pay x402 offers in RLUSD on the XRP Ledger (XRPL_SEED) and in USDC on Solana (SOLANA_PRIVATE_KEY) and Algorand (ALGORAND_MNEMONIC), and MPP sessions on Tempo (MPP_SESSION_DEPOSIT);
• send USDC.

It can only do that within the budget you set:

• You set the limits. For example: up to 5 USDC per payment and 20 USDC a day, and the agent is free to spend within them.
• Above a limit, you decide. You get a Telegram message with Approve / Deny, a request to sign in your own wallet over AC2, or the request shows up on your wallet server dashboard. No answer means no payment.
• Every signature is checked first by [presign-guard](https://presign-guard.fizzl.eu). It checks for known drainers, sanctioned addresses and look-alike tokens, checks an x402 payment against what the seller asked, and simulates a transaction to see what really leaves the wallet. A red verdict is never signed.
• When in doubt, nothing is signed. If the check, Telegram or the server can't be reached, the wallet stops.
• Paid answers are checked before your agent reads them (with a wallet server). An AI check looks at what the API sent back. If it carries instructions aimed at your agent (prompt injection: "ignore your rules", "pay this address"), the answer comes with a warnings field first that tells the agent to treat it as data only. If it isn't what was paid for, the warning says so too. You see both on the receipt and get a message.

The key stays on your machine; the server only decides whether a signature is allowed. Each check costs $0.01, paid in USDC on Base from the same wallet, or from prepaid credits.

What the limits do and don't stop. The limits are enforced by this MCP server on your computer, not on the blockchain. The agent wallet's private key is on that computer too (in the MCP config, or in a file with AGENT_KEY_FILE). An agent that can read files or run commands (Claude Code, Cursor) could read the key and sign without these rules. So give the agent its own wallet with only what you'd accept losing, never your main wallet. With the wallet server (hosted at wallet.fizzl.eu), you can also put the limit on the chain: your USDC stays in your own wallet, and the agent's wallet is topped up to a small float within a limit a day that a contract on Base keeps (agent-allowance). A leaked key can then take at most that. This server asks for the top-up by itself before a payment when its wallet runs low.

See the dashboard (demo data): https://wallet.fizzl.eu/demo

Quick start (hosted, about 2 minutes)

No keys to copy: the wallet makes its own key on your computer, and you link it to your account with a code. The hosted wallet at wallet.fizzl.eu does the limits, approvals and receipts. Free to start.

1. Install it in your app, without keys.

• Claude Desktop: download [fizzl-wallet.mcpb](https://wallet.fizzl.eu/download/claude-desktop) and open it; Claude Desktop installs it (it brings its own Node.js).
• Claude Code: claude mcp add wallet -- npx -y presign-guard-wallet-mcp@0.30.0
• Cursor and other MCP clients: { "mcpServers": { "wallet": { "command": "npx", "args": ["-y", "presign-guard-wallet-mcp@0.30.0"] } } }

1. Ask your agent: *"what is my wallet status?"* It makes its own wallet (the key goes into ~/.fizzl/agent-key, readable only by you, and is never sent anywhere) and answers with a link and a code that works for 10 minutes.
2. Open the link, sign in at wallet.fizzl.eu with e-mail, a passkey, Xaman or your wallet, and enter the code. Give the agent a name. The wallet picks up its key for the wallet server by itself; no restart.
3. Put a few dollars of USDC in the agent's wallet (the dashboard has buttons for it). Most calls cost a cent or less. Then ask something like *"find a weather API and get the forecast for Amsterdam"*. It finds a paid API, pays within your limits and shows you the receipt.

Then connect Telegram on the dashboard to approve anything above your limit from your phone, and press Test my setup to see what's still missing.

Rather paste the keys yourself? On the dashboard, Agents → Add agent shows the setup for your app with the keys filled in. Prefer to run everything yourself? See Set up below.

In ChatGPT, Claude on the web or phone, or Grok

These apps can't run a local MCP server, so they use the remote connector instead: add a custom connector with the URL https://wallet.fizzl.eu/mcp and sign in to your Fizzl wallet. The app can then search paid APIs and ask for payments, but it never pays on its own: every payment waits for your signature in your own wallet (USDC on Base or Solana, or RLUSD in Xaman). Steps per app: https://wallet.fizzl.eu/connector

Tools

No paying twice. A signed x402 payment (an EIP-3009 authorization) can be collected by the seller until it expires, also after the API answered with an error or asked again, perhaps with another payTo. So when a paid call doesn't answer properly, the wallet asks USDC on-chain whether that payment was taken (authorizationState) and says so in the result (charge, with a warning first). A second payment for the same endpoint is refused until the first one is used or expired, and for an hour after a payment that was taken without an answer, so a retry can't pay twice.

The wallet signs only what these tools need: payment signatures and transfers. It signs no EIP-7702 authorization (handing the wallet's code to a contract, which is how "sweeper" drainers empty a wallet), whatever a seller, a web page or a prompt asks.

Set up

1. Make a separate wallet for the agent. Put only what it may spend in it: a few dollars of USDC on Base, plus a little ETH for gas if it will send transfers. Never use your main wallet.
2. Optional: phone approvals.

• Create a bot with @BotFather, send it /start.
• Get your chat id from @userinfobot.

1. Add it to your MCP client. For Claude Desktop: Settings → Developer → Edit Config opens claude_desktop_config.json (on a Mac in ~/Library/Application Support/Claude/, on Windows in %APPDATA%\Claude\). Put this in it:

{

"mcpServers": { "wallet": { "command": "npx", "args": ["-y", "presign-guard-wallet-mcp@0.30.0"], "env": { "AGENT_KEY": "0x…the agent wallet's private key…", "LIMIT_USDC_PER_TX": "5", "LIMIT_USDC_PER_DAY": "20", "TELEGRAM_BOT_TOKEN": "123456:ABC…", "TELEGRAM_CHAT_ID": "123456789" } } } }

Rather keep the key out of that file? Put it in a file only you can read and set "AGENT_KEY_FILE": "/full/path/to/that/file" instead of AGENT_KEY.

For Claude Code, the key goes into a file at a prompt (not shown, not in your shell history or Claude's config):

mkdir -p ~/.fizzl && (umask 077; printf 'Agent wallet key: '; stty -echo; read -r k; stty echo; echo; printf '%s\n' "$k" > ~/.fizzl/agent-key)

claude mcp add wallet -e AGENT_KEY_FILE=$HOME/.fizzl/agent-key -e LIMIT_USDC_PER_TX=5 -e LIMIT_USDC_PER_DAY=20 -- npx -y presign-guard-wallet-mcp@0.30.0

Pin the version (@0.30.0), as above: npx -y without one fetches the newest release on every start, and that code sees the key. Releases are published from GitHub Actions with npm provenance; npm audit signatures checks it.

Then ask your agent, for example: *"Check my wallet, then get the BTC signal from https://ichimoku-signal.fizzl.eu/signal/BTC-USDT"*.

Or let it find a service itself: *"Find a paid API for a bitcoin trend signal under $0.10 and buy one"*. The agent searches the x402 catalog with find_services, picks one and pays it with pay_x402, within your limits.

One budget for all your agents

Run the wallet server and make an agent key on its dashboard. It gives you:

• one price rule and one daily budget for all your agents;
• approvals on the dashboard and on Telegram;
• an activity log.

Then use these variables instead of LIMIT_* and TELEGRAM_*:

"env": {

"AGENT_KEY": "0x…", "WALLET_SERVER_URL": "https://your-wallet-server.example", "WALLET_SERVER_KEY": "awk_…" }

Configuration

| LIMIT_NATIVE_PER_TX, LIMIT_NATIVE_PER_DAY | lim