x402 Payments

Pay for x402-gated APIs using USDC on Base. This skill enables agents to autonomously make crypto payments when accessing paid web resources.

🚨 Framework for x402 payment plumbing, not financial advice. Read DISCLAIMER.md before connecting to a wallet with real funds. Cap per-call payments with --max <USD> or the X402_MAX_PAYMENT_USD env var; the wallet should be a scoped working-capital wallet, not your treasury.

This is a template. The default x402_cli.py handles 402 detection, payment-payload construction, and balance checks. Bring your own policy for which endpoints to pay for, what max payment per call is acceptable, and how to scope the funded wallet.

Setup

1. Install the Simmer SDK

   pip install simmer-sdk

2. Set your wallet private key

   export EVM_PRIVATE_KEY=0x...your_private_key...

   Falls back to WALLET_PRIVATE_KEY if EVM_PRIVATE_KEY is not set (same key Simmer/Polymarket users already have). Your EVM address works on all chains — Polygon for trading, Base for x402 payments.
3. Fund with USDC on Base
   • Send USDC to your wallet address on Base network
   • x402 payments on Base are fully gasless — you only need USDC, no ETH
4. Install dependencies

   pip install x402[httpx,evm]

Quick Commands

Examples

Check balance

python x402_cli.py balance

x402 Wallet Balance
==============================
Address: 0x1234...5678
Network: Base Mainnet

USDC:  $42.50
ETH:   0.000000 ETH

Fetch free endpoint (no payment needed)

python x402_cli.py fetch "https://api.kaito.ai/api/v1/tokens" --json

Fetch Kaito mindshare data ($0.02/data point via x402)

python x402_cli.py fetch "https://api.kaito.ai/api/payg/mindshare?token=BTC&start_date=2026-02-13&end_date=2026-02-14" --json

Fetch Kaito sentiment data ($0.02/data point via x402)

python x402_cli.py fetch "https://api.kaito.ai/api/payg/sentiment?token=BTC&start_date=2026-02-13&end_date=2026-02-14" --json

Ask AlphaKek knowledge engine ($0.01 via x402)

python x402_cli.py fetch "https://api.alphakek.ai/x402/knowledge/ask" \
  --method POST --body '{"question": "What is the current sentiment on BTC?", "search_mode": "fast"}' --json

Fetch CoinGecko price data ($0.01 via x402)

python x402_cli.py fetch "https://pro-api.coingecko.com/api/v3/x402/simple/price?ids=bitcoin&vs_currencies=usd" --json

Fetch Simmer premium endpoint

python x402_cli.py fetch "https://x402.simmer.markets/api/sdk/context/market-123" \
  --header "Authorization: Bearer sk_live_..." --json

Quicknode RPC — blockchain calls without API keys

# Get ETH balance on Ethereum mainnet
python x402_cli.py rpc ethereum-mainnet eth_getBalance 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 latest

# Get latest block on Polygon
python x402_cli.py rpc polygon-mainnet eth_blockNumber

# Get token balance on Base
python x402_cli.py rpc base-mainnet eth_call '{"to":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","data":"0x70a08231000000000000000000000000YOUR_ADDRESS"}' latest

Quicknode x402 supports 55+ networks (Ethereum, Polygon, Base, Arbitrum, Solana, Bitcoin, and more). $10 buys 1M RPC credits — each successful call costs 1 credit.

Supported x402 Providers

Kaito API docs: https://github.com/MetaSearch-IO/KaitoX402APIDocs Quicknode x402 docs: https://x402.quicknode.com/llms.txt

Configuration

Or set via config.json in the skill directory:

{
  "max_payment_usd": 10.00,
  "network": "mainnet"
}

How It Works

1. Skill makes HTTP request to the target URL
2. If server returns 200 — done, no payment needed
3. If server returns 402 Payment Required — x402 SDK reads payment requirements
4. SDK signs a USDC transfer authorization on Base (no gas needed)
5. SDK retries request with payment signature
6. Server verifies payment, returns gated content

All payment handling is automatic via the official Coinbase x402 Python SDK.

For Other Skills

Other skills can import x402 functions directly:

from skills.x402.x402_cli import x402_fetch

# Returns parsed JSON response
data = await x402_fetch("https://api.kaito.ai/api/payg/mindshare?token=BTC")

Security

• Uses the official Coinbase x402 Python SDK for payment signing
• Private key never leaves your machine
• Max payment safety cap prevents accidental overspend
• Dry-run mode to preview payments before executing

Private key safety:

• Store your key in a .env file, never pass it inline in shell history
• Ensure .env is in your .gitignore — never commit private keys to git
• Use a dedicated hot wallet with limited funds, not your main wallet
• Rotate the key immediately if you suspect it was exposed

Troubleshooting

"EVM_PRIVATE_KEY not set"

• Set your wallet private key: export EVM_PRIVATE_KEY=0x...

"Insufficient USDC balance"

• Fund your wallet with USDC on Base network
• Run python x402_cli.py balance to check

"Payment exceeds max limit"

• Increase limit: --max 50 or set X402_MAX_PAYMENT_USD=50

"Unsupported network in payment options"

• Ensure you have USDC on Base. Some providers may offer other chains but this skill uses Base only.