# Foundry compatibility

Description: Hardhat 3's Foundry compatibility

Note: This document was authored using MDX

  Source: https://github.com/NomicFoundation/hardhat-website/tree/main/src/content/docs/docs/reference/foundry-compatibility.mdx

  Components used in this page:
    - <Install pkg="..."/>: Installs a package in the terminal with npm/pnpm/yarn.

import Install from "@hh/Install.astro";

Hardhat 3 is designed to be compatible with Foundry. Read this section to learn more about how to use Hardhat 3 with contracts built with Foundry.

## Solidity build process compatibility

You can use Hardhat 3 to build contracts and tests created with Foundry.

### Configuration

You may want to configure your Hardhat project to make it easier to work with Foundry, like setting `src/` as the main source directory. Read the [configuration](/docs/reference/configuration) reference for more information.

### Remappings

Hardhat 3 supports `remappings.txt` files by default. It automatically loads all the `remappings.txt` files in your project, and in the npm packages that your project depends on. Hardhat 3's remappings support is more advanced, and limits the scope of each remapping to the directory they are defined in, avoiding any remapping conflicts. Read more about remappings in the [Using Solidity remappings](/docs/guides/writing-contracts/remappings) guide.

#### The `@nomicfoundation/hardhat-foundry` plugin

Some Foundry projects don't use `remappings.txt` files, but instead rely on `forge` to autogenerate them. If this is the case for your project, or any of your dependencies, you should install the `@nomicfoundation/hardhat-foundry` plugin.

To install it, run:

<Install packages="@nomicfoundation/hardhat-foundry" />

Then, add it to your Hardhat config:

```ts
// hardhat.config.ts
import { HardhatUserConfig } from "hardhat/config";
// ...
import hardhatFoundry from "@nomicfoundation/hardhat-foundry";

const config: HardhatUserConfig = {
  // ... rest of the config
  plugins: [..., hardhatFoundry],
};
```

## Solidity tests compatibility

Hardhat 3 can run Solidity tests by default, including those previously built for Foundry. Learn more about writing and running Solidity tests in Hardhat 3 by reading the [Writing Solidity tests](/docs/guides/testing) guide, and the [Cheatcodes](/docs/reference/cheatcodes/cheatcodes-overview) reference documentation.

To learn how to configure the Solidity tests runner, read the [Configuration](/docs/reference/configuration#solidity-tests-configuration) reference documentation.

## Separate build process and test artifacts

Hardhat 3 builds smart contracts and tests as separate build processes. On top of that, it doesn't expose the build artifacts of tests to users, and considers them internal and part of the `cache/` directory.