YAML Template

Use the built-in YAML editor to define a DevNet template using YAML.
DevNet templates can be defined using YAML. These YAML templates are reusable, enabling you to quickly spawn highly customized DevNet environments.
YAML DevNet templates have one mandatory and multiple optional fields.
The mandatory field template is where you specify basic information about the template and the network fork configurations.
The following optional fields can be used to override on-chain data with custom values: wallets, contracts, storage, balances, and erc20.

Create a DevNet template in YAML

  1. 1.
    Log into your Tenderly account.
  2. 2.
    ​Navigate to the DevNets section and click Create Template.
  3. 3.
    Use the YAML editor to define your DevNet template.
Create DevNet templates in YAML

Mandatory fields


The mandatory template field must contain the following key-value pairs:
name: # Your template's unique name
block-number: # Desired block number (e.g., latest or 123456)
visibility: # Scope of visibility (TEAM or PERSONAL)
network-id: # Network ID number (e.g., 1 for the Ethereum Mainnet)
chain-id: # Network chain ID (e.g., 1 for Ethereum)
block-gas-limit: # Maximum amount of gas in Wei (e.g., 10000000)
base-fee-per-gas: # Base fee per gas in Wei (e.g., 1000000000)
The network name or ID, block number, template name, and visibility are pulled from the UI form automatically. However, they can be manually adjusted in the YAML editor.

Optional fields


Add the balances field to override the balance on a contract or a wallet. You can include multiple address fields at once.
- address: # contract or wallet address
amount: # custom balance


Add the erc20 field to change the balances of addresses for specific ERC-20 contracts. You can modify the balances on multiple ERC-20 contracts as well as multiple addresses within each contract at once, following the format below.
- contract: # ERC-20 token contract address
- address: # wallet or contract address
amount: 100


Add the contracts field to override the on-chain data of a specific contract with custom values. You can modify the balance on the contracts as well as storage variables.
- address: # contract address
bytecode: # contract bytecode
nonce: # 0
balance: # custom balance
slots: # format: slot address: value
- 0x34590...988c: # value
- 0x34590...c88d: # value


Add the wallets field to modify the balance on a specific wallet. You need to provide the wallet address and specify the desired balance for that wallet to have on your DevNet.
- address: # wallet address
nonce: # 0
balance: # custom balance


Add the storage field to override storage variables for contracts and wallets. The address field can be a contract or wallet address. You can include multiple address fields following the format below.
- address: # contract or wallet address
slots: # format: slot address: value
- 0x1459...3988c: # value
- 0x2459...3988c: #value

Validating the YAML template

Ensure the syntax is correct by using the built-in YAML validation tool on the Tenderly Dashboard. After successful validation, click on Create to save your template. The newly created template will now be listed under the available templates on the DevNets page.
DevNet templates cannot be modified once they have been saved.
You can use this template to spawn a DevNet environment that reflects the configurations you’ve defined in the YAML file.