Northline WebKit

Pay-per-call web tools for AI agents. x402 + USDC on Base, works over plain HTTP or as an MCP server. No API keys, no signup, no subscription: each call costs $0.001–$0.005, paid inline.

• Live API: https://northline-webkit.northline-c86.workers.dev

• MCP endpoint (Streamable HTTP): https://northline-webkit.northline-c86.workers.dev/mcp

• OpenAPI: /openapi.json · LLM docs: /llms.txt · x402 discovery: /.well-known/x402

• MCP Registry: dev.workers.northline-c86.northline-webkit/webkit

Routes and prices

All routes are GET with query parameters (* = required). Prices are per successful call, in USDC on Base.

The MCP server also exposes a free webkit_catalog tool listing every tool, price and example input.

Related MCP server: Santos Automation

How to pay (x402)

1. Call a route without payment → you get HTTP 402 with the payment requirements (accepts: scheme exact, network eip155:8453, asset USDC, amount, payTo) in the body and PAYMENT-REQUIRED header.

2. Sign the payment with any x402 client (EIP-3009 USDC authorization — gasless for you; the facilitator submits it).

3. Retry the same request with the signed payload in the PAYMENT-SIGNATURE header → 200 with the result, settlement receipt in PAYMENT-RESPONSE.

Input is validated before settlement and nothing settles on an error response, so you never pay for a bad request or an upstream failure.

import { x402Client, x402HTTPClient } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const url = "https://northline-webkit.northline-c86.workers.dev/v1/url/check?url=https://example.com";
const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.BUYER_KEY as `0x${string}`), networks: ["eip155:8453"] });
const http = new x402HTTPClient(client);

const first = await fetch(url); // 402
const required = http.getPaymentRequiredResponse((h) => first.headers.get(h), await first.json());
const payload = await client.createPaymentPayload(required);
const paid = await fetch(url, { headers: http.encodePaymentSignatureHeader(payload) });
console.log(await paid.json());

Any x402-aware agent wallet or client (e.g. AgentCash) works the same way.

Over MCP

Add the server to any MCP client that supports Streamable HTTP:

{ "mcpServers": { "northline-webkit": { "url": "https://northline-webkit.northline-c86.workers.dev/mcp" } } }

Paid tools follow the x402 MCP transport: an unpaid tools/call returns isError with the payment requirements in structuredContent; resend the call with the signed payload in params._meta["x402/payment"] and the receipt comes back in result._meta["x402/payment-response"].

Self-host

npm ci
npm test                # unit tests (mocked network)
npx wrangler deploy     # Cloudflare Workers free plan

Set PAY_TO in wrangler.toml to your own wallet. Facilitator defaults to PayAI (no key needed).

Related

• Northline ChainKit — pay-per-call onchain tools (address profile, USDC payment verify, tx explain).

License

MIT