## Compiler

Configure how Foundry compiles your Solidity contracts, including version management, optimization, and output options.

### Solidity version

By default, Foundry auto-detects the required Solidity version from your contracts. To pin a specific version:

```toml [foundry.toml]
[profile.default]
solc_version = "0.8.28"
```

Disable auto-detection if you want full control:

```toml [foundry.toml]
[profile.default]
solc_version = "0.8.28"
auto_detect_solc = false
```

### EVM version

Set the target EVM version for compilation. This affects which opcodes are available:

```toml [foundry.toml]
[profile.default]
evm_version = "cancun"
```

Common values: `paris`, `shanghai`, `cancun`, `prague` (default).

### Optimizer settings

Enable the optimizer and configure the number of runs:

```toml [foundry.toml]
[profile.default]
optimizer = true
optimizer_runs = 200
```

* **Lower runs** (e.g., 1): Optimizes for deployment cost
* **Higher runs** (e.g., 1000000): Optimizes for runtime cost (frequent calls)

For production deployments, consider higher optimizer runs:

```toml [foundry.toml]
[profile.production]
optimizer = true
optimizer_runs = 1000000
```

### Via IR

Enable the new IR-based compilation pipeline for better optimization:

```toml [foundry.toml]
[profile.default]
via_ir = true
```

This can produce more optimized bytecode but increases compilation time.

### Remappings

Map import paths to actual file locations:

```toml [foundry.toml]
[profile.default]
remappings = [
    "@openzeppelin/=lib/openzeppelin-contracts/",
    "@uniswap/=node_modules/@uniswap/",
]
```

Foundry auto-detects remappings from your `lib` folder by default. To disable:

```toml [foundry.toml]
[profile.default]
auto_detect_remappings = false
```

### Ignoring warnings

Suppress specific compiler warnings:

```toml [foundry.toml]
[profile.default]
ignored_error_codes = ["license", "code-size"]
```

Or treat all warnings as errors:

```toml [foundry.toml]
[profile.default]
deny_warnings = true
```

### Bytecode metadata

Control the metadata hash appended to bytecode:

```toml [foundry.toml]
[profile.default]
bytecode_hash = "none"  # Options: ipfs, bzzr1, none
cbor_metadata = false
```

Setting `bytecode_hash = "none"` is useful for deterministic deployments.

### Extra output

Include additional compiler output in artifacts:

```toml [foundry.toml]
[profile.default]
extra_output = ["storageLayout", "metadata"]
extra_output_files = ["ir", "irOptimized"]
```

### Example configuration

A complete compiler configuration for production:

```toml [foundry.toml]
[profile.default]
solc_version = "0.8.28"
evm_version = "cancun"
optimizer = true
optimizer_runs = 200
via_ir = false

[profile.production]
optimizer_runs = 1000000
via_ir = true
bytecode_hash = "none"
```

For the complete list of compiler options, see the [Solidity Compiler Reference](/config/reference/solidity-compiler).