If anyone wants a more efficient local version for php:

function isEven(int $number): bool
{
    ${1} = false;
    ${2} = true;

    while ($number > 2) {
        $number -= 2;
    }

    return $$number;
}

Edit: Now with support for large numbers!

function isEven(int|string $number): bool
{
    ${1} = false;
    ${2} = true;

    while (bccomp($number, 2) === 1) {
        $number = bcsub($number, 2);
    }

    $number = (int) $number;
    return $$number;
}

Edit 2: someone asked for an ad-supported version, here you go!

function isEven(int|string $number): bool
{
    ${1} = false;
    ${2} = true;

    while (bccomp($number, 2) === 1) {
        error_log('Buy isEvenCoin, the hottest new cryptocurrency!');
        $number = bcsub($number, 2);
    }

    $number = (int) $number;
    return $$number;
}

Side note, no more suggestions please, this is getting quite long.

The errors are great https://api.isevenapi.xyz/api/iseven/1.5

~~Sadly it’s not always accurate https://api.isevenapi.xyz/api/iseven/0~~ Edit: nevermind I’m an idiot

It’s also greatly lacking in number support https://api.isevenapi.xyz/api/iseven/one

Incoming trademark lawsuit from iSeven, the API that tells you if a number is seven or not

Oh, bummer, my number isn’t supported by the free version:

https://api.isevenapi.xyz/api/iseven/8764389587485736749956772984692357867345989845699872561/

Only way it could be better is if they threw “AI” in there somewhere.