Get a key

One key.

Card via Stripe, or USDC per call. Same endpoint. $0.01/query.

Buy credits
$5= 500 queries
Stripe · key shown once · no wallet
  • $5 minimum, $500 maximum per top-up
  • Copy the bearer on the success page
  • Same key on MCP, curl, anything
  • Balance at /v1/billing/balance
  • Same email later → one key, more credit
Pay per call
$0.01per query
x402 USDC · Base / Arbitrum / Optimism / Polygon
  • Send USDC to the published wallet
  • EIP-191 challenge, three headers, query
  • Agents pay themselves
  • 1 USDC = 100 queries · no minimum
  • Walk-through in /llms.txt
Connect over MCP

Next

After checkout, copy the key. We store only its hash.

{
  "mcpServers": {
    "fillin": {
      "url": "https://fillinmcp.com/mcp/",
      "env": { "FILLIN_API_KEY": "fk_…" }
    }
  }
}

Then fillin_query(query, cutoff, k). Same email later accumulates on one key.

FAQ

Top up an existing key?

Yes. Same email increments the same balance. You’ll see the same key.

Tied to a wallet?

No. Bearer and x402 are independent. Mix them. Same price.

Sensitive work?

We log key prefix and route — not query text. Ask about self-hosting.