# Migrating a plugin from Buidler to hardhat

This is a short guide explaining how to turn a Buidler plugin into a Hardhat one.

If you want a complete example of a Hardhat plugin, take a look at this repository (opens new window).

# Updating its dependencies

# Core package

References to the @nomiclabs/buidler package should be replaced with the hardhat package in your package.json, and your imports or requires.

For example, you would import the extendEnvironment function this way:

import { extendEnvironment } from "hardhat/config";

# Plugins

Similarly, references to Buidler plugins should be replaced with their corresponding Hardhat plugins. For example, @nomiclabs/buidler-ethers would be @nomiclabs/hardhat-ethers.

# Adapting your plugin's source code

Replace all types or imported names that include Buidler with Hardhat in your plugin source code.

For example, the BuidlerRuntimeEnvironment should be replaced with the HardhatRuntimeEnvironment. We suggest using hre instead of bre as its variable name.

# Artifacts

The readArtifact and readArtifactSync functions were moved to the HardhatRuntimeEnvironment so you must replace their uses like this:

const tokenArtifact = await hre.artifacts.readArtifact("Token");

The artifact format is now supplemented with build information and debug artifacts in Hardhat which allows you to read things like contract symbols. See the documentation for more information.

# Updating your plugin's tests

Apart from updating types and names, fixture projects need their buidler.config.js renamed to hardhat.config.js.

# Changes needed to your test project's config

The compiler configuration is now expected in the solidity field instead of solc. Note that Hardhat projects allow multiple solidity versions in its compilation pipeline. For more information see its documentation.

Besides that, the compiler settings now go inside a settings field. For example, a configuration like this:

module.exports = {
    solc: {
        version: "0.7.2"
        optimizer: {
            enabled: true,
            runs: 200

needs to be replaced with this:

module.exports = {
  solidity: {
    version: "0.7.2",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200,

# Adapting your type extensions

Hardhat introduced a few changes in how type extensions are created and used.

These are the necessary changes to update your plugin.

First, you need rename your src/type-extensions.d.ts file to src/type-extensions.ts.

Then, you need to add an import "./type-extensions"; in your src/index.ts file, or the main entrypoint to your plugin as defined in your package.json.

# Extending Hardhat types

Hardhat types are meant to be imported from hardhat/types, but when extending them, you should import them from the module that declares them.

For example, if you want you use the HardhatRuntimeEnvironment type, you should import it with:

import { HardhatRuntimeEnvironment } from "hardhat/types";

But if you want to extend it, you should import the module that declares it instead, which is hardhat/types/runtime.

import "hardhat/types/runtime";

declare module "hardhat/types/runtime" {
  export interface HardhatRuntimeEnvironment {
    newField: number;

# Adapting your config extensions

Config types are handled slightly differently in Hardhat.

For each config element/type, there are two Typescript types defined. One ends with UserConfig; it represents the user's input is used by users when writing their config. The other ends with just Config; it represents the configuration values after any resolution and default values have been applied, and it's used during the execution of tasks, tests and scripts, and is present in the Hardhat Runtime Environment.

For example, HardhatUserConfig represents the entire config written by the user, and all of its fields are optional. HardhatConfig, is the result of resolving/normalizing it, and applying default values. None of its fields are optional.

Some types have been renamed to match this new pattern:

  • ProjectPaths is now ProjectPathsUserConfig
  • Networks is now NetworksUserConfig
  • Both have their resolved versions: ProjectPathsConfig and NetworksConfig, respectively.

You can find an example of how to properly extend these types, resolve/normalize the users's config, and apply default values in the src/type-extensions.ts and src/index.ts files.

# How type extensions are loaded in Hardhat

Previously, type extensions were loaded by plugin users by adding references to a plugin-owned type-extensions.d.ts in their tsconfig.json.

Now, they're loaded automatically when importing the plugin in a hardhat config file. For example:

import "@nomiclabs/hardhat-ethers";

This is enough to import the type extensions included in the @nomiclabs/hardhat-ethers plugin.

# Adapting your README.md

Make sure to update the README to point to the new Hardhat site (https://hardhat.org), and that the Typescript Support section has been updated.

Last Updated: 6/29/2021, 4:42:51 PM