# Inline configuration for Solidity tests

Description: How to override fuzz and invariant test settings

Note: This document was authored using MDX

  Source: https://github.com/NomicFoundation/hardhat-website/tree/main/src/content/docs/docs/guides/testing/inline-configuration.mdx

Hardhat lets you override fuzz and invariant test settings on a per-function basis using NatSpec comments. This is useful when different tests need different parameters. For example, running more fuzz iterations on a critical function, or increasing the depth of an invariant test.

Inline overrides take precedence over the global settings defined in your [Solidity tests configuration](/docs/reference/configuration#solidity-tests-configuration).

## Syntax

Each override is a single line inside a NatSpec comment block, following the format `hardhat-config: <key> = <value>`:

```solidity
/// hardhat-config: fuzz.runs = 10000
/// hardhat-config: fuzz.maxTestRejects = 500
function testTransferFuzz(uint256 amount) public {
  // ...
}
```

Block comments are also supported:

```solidity
/**
 * hardhat-config: invariant.runs = 100
 * hardhat-config: invariant.depth = 50
 * hardhat-config: invariant.failOnRevert = true
 */
function invariantBalanceAlwaysPositive() public {
  // ...
}
```

## Supported configuration keys

| Key                         | Description                                                     |
| --------------------------- | --------------------------------------------------------------- |
| `fuzz.runs`                 | Number of fuzz iterations to run                                |
| `fuzz.maxTestRejects`       | Maximum number of rejected inputs before aborting               |
| `fuzz.showLogs`             | Whether to show console logs during fuzzing                     |
| `fuzz.timeout`              | Timeout for the fuzz test                                       |
| `invariant.runs`            | Number of invariant test runs                                   |
| `invariant.depth`           | Number of calls per run to attempt to break the invariant       |
| `invariant.failOnRevert`    | Whether to fail the invariant if a revert occurs                |
| `invariant.callOverride`    | Whether to override unsafe external calls                       |
| `invariant.timeout`         | Timeout for the invariant test                                  |
| `allowInternalExpectRevert` | Allow expecting reverts at the same callstack depth as the test |

## Foundry compatibility

Hardhat also accepts the `forge-config:` prefix, kebab-case keys, and the `default` profile, so existing Foundry inline configuration works without changes:

```solidity
/// forge-config: default.fuzz.runs = 10000
/// forge-config: fuzz.max-test-rejects = 500
function testTransferFuzz(uint256 amount) public {
  // ...
}
```