Deploying Contracts

Deploying smart contracts to Flow's networks is the final step in bringing your blockchain application to life. This guide covers everything you need to know to deploy your Cadence contracts to both Flow Testnet and Mainnet, from account creation to contract updates.

What You'll Learn

After completing this guide, you'll be able to:

• Create and fund accounts on Flow Testnet and Mainnet
• Deploy contracts using Flow CLI with proper configuration
• Update existing contracts while preserving their addresses
• Understand the differences between testnet and mainnet deployment
• Follow security best practices for production deployments

Prerequisites

Before deploying contracts, make sure you have:

• Flow CLI installed and configured
• A Flow project with contracts ready for deployment
• Basic understanding of Cadence smart contracts
• Completed testing of your contracts locally

Deployment Workflow

The recommended deployment workflow follows this progression:

1. Emulator Deployment - Deploy and test your contracts locally (free, instant)
2. Testnet Deployment - Deploy and test your contracts on Flow Testnet (free)
3. Mainnet Deployment - Deploy to Flow Mainnet once testing is complete (costs FLOW tokens)
4. Contract Updates - Update contracts as needed using the update command

This approach ensures your contracts work correctly before committing real resources to mainnet deployment.

Deploy to Emulator

The Flow Emulator is your local development environment where you can deploy and test contracts instantly without any network costs or delays. This is the first step in your deployment journey.

Start the Emulator

First, start the Flow Emulator. In a second terminal:

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flow emulator start

Create an Emulator Account

Create a local account for testing:

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flow accounts create --network emulator

When prompted:

1. Account name: Enter emulator-account
2. Select emulator as the network when prompted

This creates a new account on the emulator and adds it to your flow.json configuration.

Configure Emulator Deployment

Update your flow.json to include emulator deployment configuration:

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flow config add deployment

Follow the prompts:

1. Network: emulator
2. Account: emulator-account
3. Contract: YourContract
4. Deploy more contracts: no (or yes if you have multiple contracts)

Your flow.json will now include an emulator deployment section:

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{

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"deployments": {

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"emulator": {

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"emulator-account": ["YourContract"]

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}

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}

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}

Deploy Contract to Emulator

Deploy your contract to the local emulator:

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flow project deploy --network emulator

warning

You cannot deploy the same contract to multiple accounts on the same network with one deployment command. If you attempt to do so, you will see:

❌ Command Error: the same contract cannot be deployed to multiple accounts on the same network

Edit flow.json to remove the duplicate.

You will see output similar to:

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Deploying 1 contracts for accounts: emulator-account

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YourContract -> 0xf8d6e0586b0a20c7 (contract deployed successfully)

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🎉 All contracts deployed successfully

Test Your Emulator Deployment

Verify your contract works by running scripts and transactions:

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# Run a script to read contract state

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flow scripts execute cadence/scripts/YourScript.cdc --network emulator

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# Send a transaction to interact with your contract

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flow transactions send cadence/transactions/YourTransaction.cdc --network emulator --signer emulator-account

info

The emulator provides instant feedback and is perfect for rapid development and testing. All transactions are free and execute immediately.

Deploy to Testnet

For a more complete quickstart, visit the Getting Started guide.

• You should test your contracts, transactions and scripts on Testnet, have strong smart contract test coverage and follow the additional guidelines set out here: Smart Contract Testing Guidelines.
• Use flow init to Create a Project if you need one to practice deployment with.

Create a Testnet Account

First, you'll need a testnet account to deploy your contracts. Create one with:

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flow accounts create --network testnet

info

For security reasons, Flow Cadence does not allow accounts to have the same address on testnet, mainnet, and/or the emulator.

When prompted:

1. Account name: Enter testnet-account
2. Select testnet as the network when prompted

This creates a new account on testnet and adds it to your flow.json configuration. It also saves the private key for the new account in <account-name>.pkey and uses this file to import the key because flow.json will be visible in the repo.

danger

As with any other blockchain network, anyone with access to the private key for an account can access that account at any time without you knowing.

Fund Your Testnet Account

To deploy contracts and send transactions on testnet, you need FLOW tokens. Flow provides a faucet service to get free testnet tokens.

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flow accounts fund testnet-account

This will open the faucet in your browser. You can also navigate there manually.

1. Visit the Testnet Faucet
2. Enter your testnet account address
3. Complete any required verification (captcha, etc.)
4. Request tokens (you'll receive 100000 testnet FLOW tokens)

Check your account balance:

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flow accounts list

You will see your account details with a balance of FLOW tokens.

Configure Testnet Deployment

Update your flow.json to include testnet deployment configuration:

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flow config add deployment

Follow the prompts:

1. Network: testnet
2. Account: testnet-account
3. Contract: YourContract
4. Deploy more contracts: no (or yes if you have multiple contracts)

Your flow.json will now include a testnet deployment section:

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{

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"deployments": {

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"testnet": {

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"testnet-account": ["YourContract"]

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}

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}

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}

Deploy Contract to Testnet

Deploy your contract to the public testnet:

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flow project deploy --network testnet

You will see output similar to:

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Deploying 1 contracts for accounts: testnet-account

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YourContract -> 0x9942a81bc6c3c5b7 (contract deployed successfully)

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🎉 All contracts deployed successfully

Deploy to Mainnet

Once you've successfully tested your contracts on testnet, you can deploy to mainnet. You'll need a mainnet account with real FLOW tokens.

Create a Mainnet Account

For mainnet, you'll need to acquire FLOW tokens through exchanges or other means, as there's no faucet.

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flow accounts create --network mainnet

When prompted:

1. Account name: Enter mainnet-account
2. Select "Mainnet" Network

Acquire FLOW Tokens

You can purchase FLOW tokens from major exchanges. Make sure your mainnet account has sufficient FLOW tokens to cover deployment costs. Flow is a very efficient network, so even 1.0 FLOW is sufficient to deploy large numbers of contracts.

Configure Mainnet Deployment

Add mainnet deployment configuration to your flow.json:

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flow config add deployment --network mainnet

Follow the prompts:

1. Network: mainnet
2. Account: mainnet-account
3. Contract: YourContract
4. Deploy more contracts: no (or yes if you have multiple contracts)

Your flow.json should now include mainnet configuration:

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{

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"deployments": {

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"mainnet": {

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"mainnet-account": ["YourContract"]

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}

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}

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}

Deploy to Mainnet

Deploy your contracts to mainnet:

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flow project deploy --network mainnet

warning

This deployment costs (a relatively small amount of) real FLOW tokens and cannot be undone. You can however redeploy your contracts to update them, or delete them.

You should see output similar to:

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Deploying 1 contracts for accounts: mainnet-account

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YourContract -> 0xABC123DEF456789 (contract deployed successfully)

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🎉 All contracts deployed successfully

info

All your contract deployment addresses are stored in flow.json. Mainnet, Testnet and local (emulator) are stored as well.

Deploy updated contracts on mainnet

Contracts can be updated and retain the contract address. You can use the Flow CLI contract update command to redeploy an updated version of your contract:

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flow accounts update-contract ./YourContract.cdc --signer mainnet-account --network mainnet