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

# Smart Contracts

> Deploy, link, and call smart contracts on Celo using the MultiBaas REST API and SDK.

MultiBaas manages contracts in two layers:

* **[Library](https://docs.curvegrid.com/multibaas/manage-contracts#smart-contract-library)** — contract definitions (ABI and bytecode)
* **[On-chain](https://docs.curvegrid.com/multibaas/manage-contracts#on-chain-smart-contracts)** — deployed instances linked to a blockchain address

## Adding a Contract to the Library

You can add a contract to the library in four ways:

1. **Direct ABI upload** — paste an ABI JSON directly
2. **Solidity source upload** — MultiBaas compiles it for you
3. **Address lookup** — MultiBaas fetches the ABI from Blockscout or Etherscan by contract address
4. **Framework plugin** — automated via the [Hardhat](#hardhat) or [Forge](#foundry--forge) plugin during deployment (see below)

## Deploying or Linking a Contract

### Deploy a new contract

1. Go to **Contracts → On-chain → + → Deploy Contract**
2. Select a contract from the library
3. Fill in constructor parameters
4. Optionally enable **Sync Events** and set a starting block for event indexing
5. Submit — if using a Cloud Wallet, MultiBaas signs and submits the transaction automatically

### Link an existing contract

1. Go to **Contracts → On-chain → + → Link Contract**
2. Enter the contract address (MultiBaas can auto-fetch the ABI from a block explorer)
3. Select the contract definition from the library
4. Optionally enable **Sync Events**

## Calling Contract Methods

Once a contract is linked, MultiBaas exposes all its functions via the [REST API](https://docs.curvegrid.com/multibaas/api/multibaas-api). Toggle on Developer Mode in the contract functions UI to see sample payload, curl, TypeScript, or golang code. The base URL for all API calls is:

```
https://<deployment-id>.multibaas.com/api/v0
```

The API path uses `/chains/ethereum/` as a fixed prefix regardless of the actual EVM network. This is a MultiBaas convention — it works correctly for Celo.

### Using the TypeScript SDK

Install the [TypeScript SDK](https://www.npmjs.com/package/@curvegrid/multibaas-sdk):

```bash theme={null}
npm install @curvegrid/multibaas-sdk
```

Configure the client:

```typescript theme={null}
import * as MultiBaas from '@curvegrid/multibaas-sdk';

const config = new MultiBaas.Configuration({
  basePath: `${process.env.MULTIBAAS_DEPLOYMENT_URL}/api/v0`,
  accessToken: process.env.MULTIBAAS_API_KEY,
});

const contractsApi = new MultiBaas.ContractsApi(config);
```

**Read a contract function:**

```typescript theme={null}
const response = await contractsApi.callContractFunction(
  'my-contract-alias',  // address alias configured in MultiBaas
  'MyContract',         // contract label in the library
  'balanceOf',          // method name
  {
    args: ['0xRecipientAddress'],
    signAndSubmit: false,
  },
);

console.log(response.data.result.output);
```

**Write to a contract using a Cloud Wallet:**

```typescript theme={null}
const response = await contractsApi.callContractFunction(
  'my-contract-alias',
  'MyContract',
  'transfer',
  {
    args: ['0xRecipientAddress', '1000000000000000000'],
    from: process.env.CLOUD_WALLET_ADDRESS,
    signAndSubmit: true,
  },
);

console.log(response.data.result.tx.hash);
```

Setting `signAndSubmit: true` with a configured Cloud Wallet address instructs MultiBaas to sign and broadcast the transaction on your behalf.

**Write to a contract with an external wallet (viem):**

```typescript theme={null}
import { createWalletClient, custom } from 'viem';
import { celo } from 'viem/chains';

const walletClient = createWalletClient({
  chain: celo,
  transport: custom(window.ethereum),
});

// Get the unsigned transaction from MultiBaas
const response = await contractsApi.callContractFunction(
  'my-contract-alias',
  'MyContract',
  'transfer',
  {
    args: ['0xRecipientAddress', '1000000000000000000'],
    signAndSubmit: false,
  },
);

const tx = response.data.result.tx;

// Sign and submit with the user's connected wallet
await walletClient.sendTransaction({
  to: tx.to,
  data: tx.data,
  value: BigInt(tx.value ?? 0),
  account: userAddress,
});
```

## Framework Plugins

### Hardhat

The `hardhat-multibaas-plugin` automatically uploads and links contracts in your MultiBaas deployment as part of your Hardhat deploy scripts.

```bash theme={null}
npm install --save-dev hardhat hardhat-multibaas-plugin @nomicfoundation/hardhat-ignition
```

See the [plugin repository](https://github.com/curvegrid/hardhat-multibaas-plugin) for setup instructions.

### Foundry / Forge

The `forge-multibaas` plugin provides the same integration for Foundry-based projects.

```bash theme={null}
forge install curvegrid/forge-multibaas
```

See the [plugin repository](https://github.com/curvegrid/forge-multibaas) for setup instructions.