# Using multiple versions of Solidity in a single project

Description: How to use multiple versions of Solidity in a single project

Note: This document was authored using MDX

  Source: https://github.com/NomicFoundation/hardhat-website/tree/main/src/content/docs/docs/cookbook/multiple-solidity-versions.mdx

Some projects need to compile different files with different Solidity versions. Hardhat lets you define multiple compiler configurations using an extended format of the `solidity` property, which has a `compilers` array with different compiler configurations.

```ts
// hardhat.config.ts
import { defineConfig } from "hardhat/config";

export default defineConfig({
  // ...
  solidity: {
    compilers: [
      {
        version: "0.7.6",
      },
      {
        version: "0.8.11",
      },
      {
        version: "0.8.29",
        settings: {
          optimizer: { enabled: true },
        },
      },
    ],
  },
});
```

Hardhat compiles each Solidity file in your project using the **highest configured Solidity version** that's compatible with the version pragma of the file and its dependencies.

For example, given the configuration above:

- A file with `pragma solidity ^0.8.0` will be compiled with Solidity `0.8.29`, even though `0.8.11` is also compatible.
- A file with `pragma solidity ^0.7.0` will use Solidity `0.7.6`, which is the only valid matching version.
- A file with `pragma solidity ^0.8.0` that imports another file with `pragma solidity <0.8.20` will be compiled with `0.8.11`, because the combination of both restrictions makes it the highest compatible version.

## Overriding version selection for a file

If you need to compile specific files using a different compiler version than Hardhat's default choice, you can handle this with the `overrides` property:

```ts
// hardhat.config.ts
import { defineConfig } from "hardhat/config";

export default defineConfig({
  //...
  solidity: {
    compilers: [
      /* configured compilers */
    ],
    overrides: {
      "contracts/Foo.sol": {
        version: "0.8.11",
      },
    },
  },
});
```

In this case, `contracts/Foo.sol` will always be compiled with Solidity 0.8.11, regardless of the versions defined in `solidity.compilers`, its `pragma`, and those of its dependencies.

Each entry in the `overrides` object maps a file to a custom compiler configuration. Just like the main configuration, only the `version` field is mandatory.

### Using overrides without multiple versions of Solidity

You can use overrides even if you're using a single Solidity version. You'll need to use the extended format of the `solidity` property, with an array of `compilers` and an `overrides` object.

For example, you can enable the optimizer only for a single file:

```ts
// hardhat.config.ts
import { defineConfig } from "hardhat/config";

export default defineConfig({
  //...
  solidity: {
    compilers: [
      {
        version: "0.8.29",
      },
    ],
    overrides: {
      "contracts/Foo.sol": {
        version: "0.8.29",
        settings: {
          optimizer: {
            enabled: true,
          },
        },
      },
    },
  },
});
```