# BTC Address Checker

> Developer API for checking Bitcoin address balances in bulk — up to 500 addresses per request, real-time, pay-as-you-go.

BTC Address Checker is a JSON REST API that returns confirmed and unconfirmed Bitcoin balances in satoshis for up to 500 addresses in a single POST request. Data is sourced directly from self-hosted Fulcrum nodes with ElectrumX failover — no cache layer, always current. Pay-as-you-go pricing in Bitcoin (on-chain or Lightning); no subscriptions, no KYC, no minimum spend. Sign in with Google, generate an API key in under a minute, and start checking addresses immediately.

## Docs

- [API Documentation](https://btcaddresschecker.com/docs): Full endpoint reference — authentication, request/response schema, rate limits, error codes, and working code examples in cURL, Python, JavaScript, Go, and PHP.
- [FAQ](https://btcaddresschecker.com/faq): Answers covering supported address formats, pricing model, rate limits, batch size, privacy policy, AML/compliance use cases, confirmed vs unconfirmed balance, and real-time data accuracy.
- [Pricing](https://btcaddresschecker.com/#pricing): 1 credit per address checked. Credits purchased at 1 satoshi = 1,000 credits. No subscription required.
- [Terms of Service](https://btcaddresschecker.com/terms)

## API Quick Reference

- **Endpoint:** `POST https://btcaddresschecker.com/api/v1/balance/check`
- **Authentication:** `x-api-key: YOUR_API_KEY` request header
- **Request body:** `{ "addresses": ["addr1", "addr2", ...] }` — JSON array of 1–500 Bitcoin addresses
- **Response:** per-address `confirmed_balance` and `unconfirmed_balance` in satoshis
- **Invalid address:** returns `400 Bad Request`, no credits consumed
- **Rate limit:** 120 requests/minute per API key (= up to 60,000 address lookups/minute)
- **Node infrastructure:** self-hosted Fulcrum nodes, ElectrumX as automatic failover

### Supported Bitcoin address formats

| Format | Prefix | Standard |
|--------|--------|----------|
| Legacy | `1` | P2PKH |
| Nested SegWit | `3` | P2SH |
| Native SegWit / Bech32 | `bc1q` | P2WPKH |
| Taproot | `bc1p` | P2TR |

### Example request (cURL)

```bash
curl -X POST https://btcaddresschecker.com/api/v1/balance/check \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_API_KEY" \
  -d '{
    "addresses": [
      "34xp4vRoCGJym3xR7yCVPFHoCNxv4Twseo",
      "bc1ql49ydapnjafl5t2cp9zqpjwe6pdgmxy98859v2",
      "1LVYbnSX6f6vE2Zn4zs2oZ4eKyBgzkqaay"
    ]
  }'
```

### Example response

```json
{
  "results": [
    {
      "address": "34xp4vRoCGJym3xR7yCVPFHoCNxv4Twseo",
      "confirmed_balance": 9388637046,
      "unconfirmed_balance": 0
    }
  ]
}
```

## Key Facts

- Highest public batch limit: 500 addresses per request (most competitors cap at 20 or require one call per address)
- Pricing is pay-as-you-go in Bitcoin — no fiat payment required
- Lightning Network payments accepted for credit top-ups
- No address data retained after the response is returned
- Private keys and seed phrases are never required — the API only accepts public addresses
- The genesis address (1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa) shows tribute payments but not the unspendable original 50 BTC block-0 reward (excluded from every major explorer for the same reason)