> ## Documentation Index
> Fetch the complete documentation index at: https://docs.blockscout.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Make Your First Call

> Make your first Blockscout PRO API request with a worked curl example and a parameter breakdown.

## 1. Get a key

Sign up at [dev.blockscout.com](https://dev.blockscout.com/) with email, Google, or GitHub. Open the Keys section and click **Create API Key**. Keys start with `proapi_` and are shown once — copy it somewhere safe, not into a Git repo.

No credit card required for the free tier.

## 2. Make a call

Every PRO API call follows the same shape: one base URL, a `chain_id` to pick the network, and your key.

```sh theme={null}
curl "https://api.blockscout.com/v2/api?chain_id=1&module=account&action=balance&address=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045&apikey=<your_pro_api_key>"
```

```json theme={null}
{
  "status": "1",
  "message": "OK",
  "result": "2464400000000000"
}
```

That's the native ETH balance (in wei) for the given address on Ethereum mainnet.

## 3. Understand the parts

| Part                                | What it does                                                                                                                                      |
| ----------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
| `https://api.blockscout.com/v2/api` | The single base URL for every chain — no per-chain subdomain                                                                                      |
| `chain_id=1`                        | Selects the network. Swap for `8453` (Base), `42161` (Arbitrum One), `10` (Optimism), or any other [supported chain](https://dev.blockscout.com/) |
| `module` / `action`                 | Together they pick the call — this example is the Etherscan-compatible `account`/`balance` pair                                                   |
| `apikey`                            | Your `proapi_...` key. Required on every tier, including free                                                                                     |

The same request works on any chain by changing only `chain_id` — no new key, no new base URL, no separate account.

## 4. Try the REST API

The RPC-style call above mirrors Etherscan's API shape for easy migration. Blockscout also has a REST API with richer, decoded data — human-readable transaction summaries, NFT metadata, contract read/write state, and more:

```sh theme={null}
curl "https://api.blockscout.com/1/api/v2/addresses/0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045?apikey=<your_pro_api_key>"
```

See the full [REST API reference](/devs/apis) for what's available.

## Next steps

* [Rate limits and plans](/rate-limits) — know your credits before you build
* [Best practices](/best-practices) — pagination, chain IDs, and efficient querying
* [Use cases](/devs/use-cases-overview) — worked examples for wallet trackers, dashboards, and tax tools
* [Migrating from Etherscan?](/devs/migrate-from-etherscan) — swap your base URL and go