LLM Prompt L402 API

GPT-4o-mini access with 128 token limit. Quick AI completions.

500 sats per call, paid over the Lightning Network. No API key and no signup: the first request answers 402 Payment Required with a Lightning invoice, and repeating the request with the proof of payment returns your data.

l402_llm_prompt 500 sats

Parameters

prompt Your prompt text

Call it with curl

The first call answers 402 with a Lightning invoice in the WWW-Authenticate header. Pay it from any Lightning wallet, then repeat the call with the L402 token and preimage.

cURL

curl -X POST https://lightningfaucet.com/api/ \
  -H "Content-Type: application/json" \
  -H "Authorization: L402 $MACAROON:$PREIMAGE" \
  -d '{"action":"l402_llm_prompt","prompt":"Summarize the Lightning Network in two sentences."}'

What comes back

A successful call returns JSON, with the delivered content merged over the standard L402 receipt fields. Example values, not live data.

JSON

{
    "success": true,
    "http_code": 200,
    "service": "llm_prompt",
    "timestamp": "2026-09-11T15:04:05+00:00",
    "paid_sats": 500,
    "response": "The Lightning Network settles Bitcoin payments in payment channels held between two parties, so only the opening and closing balances touch the chain. That keeps transfers near-instant and the fees measured in fractions of a sat.",
    "model": "gpt-4o-mini",
    "tokens_used": 94,
    "prompt_tokens": 31,
    "completion_tokens": 63
}

Call it from an AI agent

With lightning-wallet-mcp the payment is handled for you. From the CLI:

Terminal

lw pay-api "https://lightningfaucet.com/api/l402/llm_prompt?prompt=Summarize+the+Lightning+Network+in+two+sentences."

In Claude Code, Cursor or any MCP host, ask the agent to call pay_l402_api with that URL. The fee is 1% of the price, rounded down, so calls under 100 sats carry no platform fee.

Questions

How much does the LLM Prompt API cost?
Each call costs 500 sats, paid as a Lightning invoice at request time. There is no subscription, no minimum and no monthly bill: you are charged for the calls you make.

Do I need an API key or an account?
No. Payment is the authentication. The first request answers 402 Payment Required with a Lightning invoice; settling it returns a preimage that authenticates the retry.

What does LLM Prompt return?
A JSON object carrying response, model, tokens_used, prompt_tokens and completion_tokens. See the example response above for the exact shape.

Related endpoints

Summarize 100 sats Keywords 50 sats Sentiment 50 sats Ask a Human 500 sats Ask a Human: Result Free Bid Board 10-500 sats

All AI/LLM Utilities endpoints · How L402 authentication works · List your own API on the gateway