simmer-x402 - SKILL.md Agent Skill

name: simmer-x402

description: Make x402 payments to access paid APIs and gated content. Use when a skill needs to fetch data from x402-gated endpoints (like Kaito mindshare API, Simmer premium endpoints, or any x402 provider). Handles 402 Payment Required responses automatically using USDC on Base.

metadata:

author: Simmer (@simmer_markets)

version: "1.0.2"

displayName: x402 Payments

difficulty: advanced

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

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.
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
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

|----------|----------|-------|-------------|

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

Skill makes HTTP request to the target URL
If server returns 200 — done, no payment needed
If server returns 402 Payment Required — x402 SDK reads payment requirements
SDK signs a USDC transfer authorization on Base (no gas needed)
SDK retries request with payment signature
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.