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

# App developer quickstart

> Get testnet ETH, deploy your first contract to OP Sepolia, and bridge assets - your first steps on the Superchain.

OP Stack chains are [EVM equivalent](/op-stack/protocol/differences): everything you know from Ethereum works here, and everything you build here works across the OP Stack ecosystem.
This quickstart takes you from zero to a deployed contract on the OP Sepolia testnet, using only free testnet funds.

<Info>
  No real funds are needed at any point — everything below runs on testnets.
</Info>

## Before you start

You'll need:

* A wallet you control (any EVM wallet works; you'll export or generate a private key for testnet use only).
* A terminal with `curl` available.

<Warning>
  Use a fresh, testnet-only private key for tutorials. Never paste a key that holds real funds into a terminal.
</Warning>

<Steps>
  <Step title="Get testnet ETH">
    Grab free OP Sepolia ETH from the [Superchain Faucet](https://console.optimism.io/faucet).
    Other options are listed on the [testnet faucets page](/app-developers/tools/faucets).
  </Step>

  <Step title="Connect to OP Sepolia">
    OP Sepolia's public RPC endpoint is `https://sepolia.optimism.io` and its chain ID is `11155420`.
    Verify you can reach it:

    ```bash theme={null}
    curl -s -X POST -H "Content-Type: application/json" \
      --data '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}' \
      https://sepolia.optimism.io
    ```

    Expected result: `{"jsonrpc":"2.0","id":1,"result":"0xaa37dc"}` (`0xaa37dc` = 11155420).
    For other networks and production-grade endpoints, see [Networks](/app-developers/reference/networks) and [RPC providers](/app-developers/reference/rpc-providers).
  </Step>

  <Step title="Deploy your first contract">
    Follow the [Deploy a contract to OP Sepolia](/app-developers/tutorials/deploy-a-contract) tutorial.
    It walks you through installing Foundry, deploying a small `Greeter` contract, and reading and writing to it from the command line — the same workflow you'd use on Ethereum.
  </Step>

  <Step title="Bridge ETH between L1 and L2 (optional)">
    Apps often need to move assets between Ethereum and an OP Stack chain.
    Start with [Bridging basics](/app-developers/guides/bridging/basics) to understand the model, then follow the [Bridging ETH with Viem](/app-developers/tutorials/bridging/cross-dom-bridge-eth) tutorial to do a Sepolia → OP Sepolia deposit programmatically.
  </Step>
</Steps>

## Where to go next

<CardGroup cols={2}>
  <Card title="Build apps on OP Stack chains" href="/app-developers/guides/building-apps">
    Development workflow, tooling, and what (little) is different from Ethereum.
  </Card>

  <Card title="Test your apps" href="/app-developers/guides/testing-apps">
    Test against OP Stack chains locally and in CI.
  </Card>

  <Card title="Go cross-chain with interop" href="/app-developers/guides/interoperability/get-started">
    Build apps that span multiple Superchain chains.
  </Card>

  <Card title="Integrate DeFi with the Actions SDK" href="/app-developers/quickstarts/actions">
    Lend, borrow, and swap with lightweight, type-safe modules (early preview — not production-ready).
  </Card>
</CardGroup>

## Need help?

* Ask a question or report documentation issues on the [Optimism monorepo issue tracker](https://github.com/ethereum-optimism/optimism/issues).