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.

When to Use This Skill

Use this skill when:

• A skill or agent needs to fetch data from an x402-gated API (e.g., Kaito mindshare)
• You encounter HTTP 402 Payment Required responses
• You need to check your Base wallet balance (USDC + ETH)
• You want to pay for Simmer premium endpoints beyond free tier rate limits

Setup

1. 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.

2. 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

3. Install dependencies

   pip install x402[httpx,evm]
   

Quick Commands

Command	Description
python x402_cli.py balance	Check USDC and ETH balances on Base
python x402_cli.py fetch <url>	Fetch URL with automatic x402 payment
python x402_cli.py fetch <url> --json	Same but output raw JSON only
python x402_cli.py fetch <url> --dry-run	Show payment info without paying
python x402_cli.py fetch <url> --max 5.00	Override max payment limit
python x402_cli.py rpc <network> <method> [params...]	Make RPC call via Quicknode x402

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

Provider	Endpoint	Price	Description
Kaito	/api/payg/mindshare	$0.02/data point	Token mindshare time series
Kaito	/api/payg/sentiment	$0.02/data point	Token sentiment time series
Kaito	/api/payg/narrative_mindshare	$0.02/data point	Narrative mindshare time series
Kaito	/api/payg/smart_followers	$0.20/request	Smart follower metrics
AlphaKek	/x402/knowledge/ask	$0.01/request	AI knowledge engine (POST, search_mode: fast/deep/ultrafast)
CoinGecko	/api/v3/x402/simple/price	$0.01/request	Token price data
Simmer	/api/sdk/context/:id	$0.005/request	Market context (rate limit bypass)
Simmer	/api/sdk/briefing	$0.005/request	Portfolio briefing (rate limit bypass)
Simmer	/api/sdk/markets/import	$0.005/request	Market import (daily quota bypass)
Quicknode	/:network (55+ networks)	$10/1M credits	Pay-per-request RPC access (no API key needed)

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

Configuration

Setting	Environment Variable	Default	Description
Wallet key	EVM_PRIVATE_KEY	(required)	Hex-encoded private key (falls back to WALLET_PRIVATE_KEY)
Max payment	X402_MAX_PAYMENT_USD	10.00	Safety cap per request
Network	X402_NETWORK	mainnet	mainnet or testnet

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.