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## `toBase64`

### Signature

```solidity
function toBase64(bytes calldata data) external pure returns (string memory);
function toBase64(string calldata data) external pure returns (string memory);
function toBase64URL(bytes calldata data) external pure returns (string memory);
function toBase64URL(string calldata data) external pure returns (string memory);
```

### Description

Encodes a `bytes` or `string` value to a base64 string. `toBase64` uses the standard alphabet (RFC 4648 section 4, with `+` and `/`), while `toBase64URL` uses the URL-safe alphabet (section 5, with `-` and `_`).

Useful for building data URIs, JWT-style payloads, or fixtures for contracts that consume base64 input.

### Parameters

| Parameter | Type                 | Description         |
|-----------|----------------------|---------------------|
| `data`    | `bytes` or `string`  | The value to encode |

### Returns

| Type     | Description                |
|----------|----------------------------|
| `string` | The base64-encoded value   |

### Examples

```solidity [test/ToBase64.t.sol]
function testToBase64() public view {
    string memory s = "forge";
    bytes memory b = hex"fbff";
    assertEq(vm.toBase64(s), "Zm9yZ2U=");
    assertEq(vm.toBase64(b), "+/8=");
    assertEq(vm.toBase64URL(b), "-_8=");
}
```

### Related Cheatcodes

* [`toString`](/reference/cheatcodes/to-string) - Convert values to strings
* [`ffi`](/reference/cheatcodes/ffi) - Call external programs, which often exchange base64 data