Chart Splat (x402)

Generate beautiful charts by paying per request with x402 micropayments — no signup, no API key, no subscription. The agent's wallet pays ~$0.005 USDC on Base mainnet for each chart.

This is the wallet-based counterpart to the standard chart-splat skill (which authenticates with an API key). Use whichever fits the user's setup.

Prerequisites

• An EVM wallet with ≥ $0.05 USDC on Base mainnet (eip155:8453)
• Private key exported as X402_PRIVATE_KEY (a hex string starting with 0x)
• Node.js 20+

The buyer never submits an on-chain transaction directly. The Coinbase x402 facilitator handles settlement and pays gas. See references/x402-protocol.md for protocol detail.

Supported Chart Types

| Type | Best For | |------|----------| | line | Trends over time | | bar | Comparing categories | | pie | Parts of a whole | | doughnut | Parts of a whole (with center space) | | radar | Multivariate comparison | | polarArea | Comparing categories with radial layout | | candlestick | Financial/crypto OHLC price data | | ohlc | Financial/crypto OHLC price data (bar variant) |

Method 1: CLI (Preferred)

Use the chartsplat-x402 CLI via npx — no install required.

npx -y chartsplat-x402-cli bar \
  --labels "Q1,Q2,Q3,Q4" \
  --data "50,75,60,90" \
  --title "Quarterly Revenue" \
  --color "#8b5cf6" \
  -o chart.png

The CLI handles the full x402 flow: sends the request, signs the EIP-3009 authorization on the 402 response, retries with the PAYMENT-SIGNATURE header, and saves the resulting PNG. On success, it prints a BaseScan URL for the settlement transaction.

CLI Options

| Flag | Description | |------|-------------| | -l, --labels <csv> | Comma-separated labels | | -d, --data <csv> | Comma-separated numeric values | | -t, --title <text> | Chart title | | --label <text> | Dataset label for legend | | -c, --color <hex> | Background color | | -w, --width <px> | Image width (default: 800) | | --height <px> | Image height (default: 600) | | -o, --output <file> | Output file path (default: chart.png) | | --config <file> | JSON config file for complex charts | | --private-key <key> | Wallet key (or set X402_PRIVATE_KEY) |

CLI Chart Commands

npx -y chartsplat-x402-cli line       -l "Mon,Tue,Wed,Thu,Fri" -d "100,200,150,300,250" -o line.png
npx -y chartsplat-x402-cli bar        -l "A,B,C"       -d "10,20,30"  -o bar.png
npx -y chartsplat-x402-cli pie        -l "Red,Blue,Green" -d "30,50,20" -o pie.png
npx -y chartsplat-x402-cli doughnut   -l "Yes,No,Maybe" -d "60,25,15" -o doughnut.png
npx -y chartsplat-x402-cli radar      -l "Speed,Power,Range,Durability,Precision" -d "80,90,70,85,95" -o radar.png
npx -y chartsplat-x402-cli polararea  -l "N,E,S,W"     -d "40,30,50,20" -o polar.png
npx -y chartsplat-x402-cli candlestick --config ohlc.json -o chart.png

Candlestick Charts

Candlestick and OHLC charts require a JSON config file since the data format is more complex than a simple CSV list. Use --config to provide a file with OHLC data points.

npx -y chartsplat-x402-cli candlestick --config ohlc.json -o candlestick.png

Config format (ohlc.json):

{
  "type": "candlestick",
  "data": {
    "datasets": [{
      "label": "VVV Price",
      "data": [
        { "x": 1740441600000, "o": 4.23, "h": 4.80, "l": 4.10, "c": 4.45 },
        { "x": 1740528000000, "o": 4.45, "h": 5.50, "l": 4.30, "c": 5.34 },
        { "x": 1740614400000, "o": 5.34, "h": 6.20, "l": 5.10, "c": 5.97 }
      ]
    }]
  }
}

Each OHLC data point requires: x (numeric timestamp in ms, or a date string like "2025-02-25"), o (open), h (high), l (low), c (close).

Complex Charts via Config File

For multi-dataset or customized charts, write a JSON config file then pass it to the CLI:

npx -y chartsplat-x402-cli bar --config chart-config.json -o chart.png

See examples/sample-charts.json for ready-to-use config samples and chartsplat.com/docs for the full schema.

Method 2: Programmatic (@x402/fetch)

For embedding directly in TypeScript/JavaScript:

const { wrapFetchWithPayment, x402Client } = require('@x402/fetch');
const { registerExactEvmScheme } = require('@x402/evm/exact/client');
const { privateKeyToAccount } = require('viem/accounts');

const account = privateKeyToAccount(process.env.X402_PRIVATE_KEY);
const client = new x402Client();
registerExactEvmScheme(client, { signer: account });
const fetchWithPayment = wrapFetchWithPayment(fetch, client);

const res = await fetchWithPayment('https://api.chartsplat.com/chart', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    type: 'bar',
    data: { labels: ['A', 'B'], datasets: [{ data: [1, 2] }] },
  }),
});
const { image } = await res.json();

Use the v2 @x402/* packages — the legacy unscoped x402-fetch@1.x will not work with the chart-splat server. See references/x402-protocol.md.

Environment Variables

| Variable | Default | Description | |----------|---------|-------------| | X402_PRIVATE_KEY | (required) | Hex private key for the paying wallet | | CHARTSPLAT_API_URL | https://api.chartsplat.com | API base URL — override to point at a testnet server |

Testnet (Base Sepolia)

Pointing at a Base Sepolia chart-splat server:

export CHARTSPLAT_API_URL=https://your-sepolia-server.example.com
npx -y chartsplat-x402-cli bar -l "A,B,C" -d "1,2,3" -o chart.png

Get test USDC from the Circle faucet (select Base Sepolia).

Output Handling

• Charts are saved as PNG files at the specified output path (default: chart.png)
• For messaging platforms (Discord, Slack), return the file path: MEDIA: /path/to/chart.png
• The CLI prints a settlement transaction URL on success for buyer auditing

Error Handling

| Error | Cause | Fix | |-------|-------|-----| | wallet private key required | Missing wallet | Export X402_PRIVATE_KEY or pass --private-key | | settlement failed (second 402) | Wallet has insufficient USDC | Top up; ~$0.01 per chart is enough headroom | | 402 keeps repeating | Wrong package version (v1 vs v2) | Confirm chartsplat-x402-cli is up to date | | no scheme matches | Network mismatch | Server advertises eip155:8453 — don't override the network on the client | | Signature rejected after long delay | Validity window (default 1h) expired | Re-run; system clock skew may also cause this |

See references/x402-protocol.md for protocol gotchas.

Tips

• The CLI accepts the full Chart Splat request body via --config — see examples/sample-charts.json for ready-to-use samples or chartsplat.com/docs for the full schema
• For pie/doughnut charts, pass an array of colors via --config so each segment gets a distinct color
• Default dimensions (800x600) suit most uses; raise via options.width / options.height for presentations
• Settlement is logged with a BaseScan URL — keep these for accounting