API docs.

Document summarization for AI agents. $0.05 per call. No subscriptions. No API keys. No signups.

Why hundun?

Cheap. $0.05 per document. Cheaper than running your own LLM stack on most providers, and orders of magnitude cheaper than enterprise summarization APIs.

Long. Up to 200,000 characters per call. Most APIs cap at 30K.

Multilingual. Auto-detects language. Outputs in the same language as input.

Pay only when you use it. No monthly minimums. No per-seat fees. Each call is one signed micropayment over x402.

Quickstart (Node.js)

1. Install

npm install x402-fetch viem

2. Set your wallet

You need a Base mainnet wallet with a small USDC balance.

# .env
PRIVATE_KEY=0x<your 64-char hex private key>

Note: if you copy a private key from MetaMask, it doesn't include the 0x prefix. Add it manually.

3. Call the API

import { wrapFetchWithPayment } from 'x402-fetch'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`)
const fetchWithPay = wrapFetchWithPayment(fetch, account)

const res = await fetchWithPay('https://api.hundun.app/api/summarize', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    pdfUrl: 'https://arxiv.org/pdf/2304.05128.pdf'
  })
})

const data = await res.json()
console.log(data.summary)

That's it. The first request returns 402 Payment Required. wrapFetchWithPayment automatically signs the payment and retries — you only see the final response.

Endpoints

POST /api/summarize

Summarize a document.

Field	Value
Price	$0.05 USDC
Network	Base mainnet
Max input	200,000 characters

Request body

JSON, one of:

{ "pdfUrl": "https://example.com/paper.pdf" }

or

{ "text": "Long text content to summarize..." }

Response (200 OK)

{
  "summary": "TL;DR: ...\n\nKey Points:\n1. ...",
  "input_length": 193188
}

Notes

• Output language matches input
• Tested with Chinese and English; other major languages likely work
• Inputs longer than 200K characters are truncated

Errors

• 400 — missing pdfUrl or text
• 402 — payment required (handled automatically by x402 clients)
• 5xx — transient issue, retry

FAQ