# How to pay for Recall Kitchen MCP tools with x402

> Source: <https://dev.to/recallkitchen/how-to-pay-for-recall-kitchen-mcp-tools-with-x402-23fc>
> Published: 2026-10-30 23:09:24+00:00

Recall Kitchen's MCP server lets AI agents look up government-published product, food, vehicle and drug recalls. Most lookups are free; past the free quota (and for photo search) an agent can pay per call with x402 in USDC on Base. Here's exactly how.

(Disclosure: I build Recall Kitchen.)

Docs: [https://recallkitchen.com/docs?utm_source=devto&utm_campaign=x402_howto](https://recallkitchen.com/docs?utm_source=devto&utm_campaign=x402_howto)

You don't need an account to keep using the server. A few anonymous searches per IP are free (5 an hour, 15 a day), and photo search is never in that free quota. After the quota, an x402-capable client can pay per call: $0.025 in USDC on Base. When a call needs payment, the server returns a normal JSON-RPC result whose content is an x402 "Payment Required" challenge (HTTP 200, `isError: true`), not a bare HTTP 402. Your client pays it and retries. The price and pay-to address are published at [`https://app.recallkitchen.com/.well-known/x402`](https://app.recallkitchen.com/.well-known/x402?utm_source=devto&utm_campaign=x402_howto). x402 covers search and photo search only. Account tools like watches and inventory need a free API key instead. The full rules are in the [docs](https://recallkitchen.com/docs?utm_source=devto&utm_campaign=x402_howto) and the [API Terms](https://recallkitchen.com/api-terms?utm_source=devto&utm_campaign=x402_howto#x402).

`POST https://app.recallkitchen.com/mcp`
`https://app.recallkitchen.com/.well-known/x402`
| Tool | Free anonymous quota | x402 / API key | 
|---|---|---|
| `search_product_recalls` (and other non-photo search tools) | Yes — a few calls per IP (docs/API terms: 5/hour, 15/day) | After the IP quota, pay with x402 **or** send an API key | 
| `search_product_recalls_from_image` (photo, beta) | **No** — never in the free anonymous quota | Always needs an API key **or** x402 | 

Account tools (watches, inventory, notifications, key management) do **not** accept x402; use a free API key from `signup` / Integrations.

For MCP tool calls that require payment, the server answers **HTTP 200** with a JSON-RPC `tools/call` result whose content is an x402 **Payment Required** payload (`isError: true`). That HTTP 200 + JSON-RPC payment challenge is correct for this MCP integration — clients should not expect a bare HTTP 402 on the MCP POST for tool payment.

Live example (image search, unpaid), truncated:

```
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "isError": true,
    "structuredContent": {
      "error": "Payment Required",
      "x402Version": 2,
      "accepts": [{
        "scheme": "exact",
        "network": "eip155:8453",
        "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
        "amount": "25000",
        "payTo": "0x8E2d8e2850Baf623A8A886DE7c80CDfB83a5cfa3",
        "maxTimeoutSeconds": 60,
        "extra": { "name": "USD Coin", "version": "2" }
      }],
      "resource": {
        "url": "mcp://tool/search_product_recalls_from_image",
        "description": "Photo (beta): identify products in an image URL, data URI, or MCP image content",
        "mimeType": "application/json"
      }
    }
  }
}
```

`amount` is USDC **atomic units** (6 decimals): `"25000"` = **$0.025**. The well-known document publishes the same price as decimal `"0.025"`.

From `/.well-known/x402` and the live challenge (they match):

| Field | Value | 
|---|---|
| Network | Base mainnet — `eip155:8453` | 
| Asset | USDC on Base — `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913` | 
| Currency | USDC | 
| Price | **$0.025 per call** (unless a live challenge states otherwise) | 
| Pay to | `0x8E2d8e2850Baf623A8A886DE7c80CDfB83a5cfa3` | 
| Scheme | `exact` | 
| x402 version | 2 | 

Do not invent other prices; always prefer the live `accepts[]` on the challenge.

`https://app.recallkitchen.com/mcp` (streamable HTTP / JSON-RPC). Prefer a free API key (`X-API-Key: rk_...` for Grok, or `Authorization: Bearer rk_...` for Claude/Cursor) when you have one — that skips x402 for search tools.`search_product_recalls` after the free IP quota, or `search_product_recalls_from_image` any time without a key).`accepts[0]` (network, asset, amount, payTo).`X402_EVM_PRIVATE_KEY` and registers scheme `eip155:8453`), sign and settle the `payTo` for `amount` atomic units on Base.

```
export X402_EVM_PRIVATE_KEY=0x...   # Base wallet funded with USDC (+ gas)
cd examples/go
go run ./search_product_recalls -query spinach -location Iowa
```

Or set `RK_API_KEY` / `RECALL_KITCHEN_API_KEY` instead of paying per call.

`GET https://app.recallkitchen.com/.well-known/x402`` tools/call` → `/mcp` (HTTP 200 + Payment Required JSON-RPC)