Starts Noita from the given path, optionally with a specific seed set.

start-noita.ps1

function Start-Noita {
    <#
        .SYNOPSIS
        Starts Noita from a PowerShell prompt, optionally with a specific set seed for a new game.
        
        .DESCRIPTION
        To use this function, copy and paste the complete function definition into a PowerShell
        session, and then invoke it with `Start-Noita`. Supply `-Seed somevalue` if you would like
        to run a specific seed (see the examples below).
        
        .EXAMPLE
        PS> Start-Noita
        
        Starts Noita normally.
        
        .EXAMPLE
        PS> Start-Noita -Seed 1
        
        Starts Noita with a fixed seed value of 1.
        
        .EXAMPLE
        PS> Start-Noita -Seed 1 -Path C:\Noita\noita.exe
        
        Starts Noita from the requested location with a fixed seed value of 1.
        Use this form if your copy of Noita was not installed via Steam, or modify the default
        setting for $Path below before loading the function into your PowerShell session.
        
        .NOTES
        If you want, you can load this function into your PowerShell profile as follows:
        
        1. Copy the entire function definition from top to bottom to your Windows clipboard (Ctrl+C).
        2. Run the following code in PowerShell:
        
            Get-Clipboard | Add-Content -Path $profile
        
        3. Close and reopen PowerShell to load the newly modified profile.
        4. Run `Start-Noita` directly as needed. It will be automatically loaded in any future PowerShell sessions.
    #>
    [CmdletBinding(DefaultParameterSetName = 'Default')]
    param(
        [Parameter()]
        [string]
        $Path = "C:\Program Files (x86)\Steam\steamapps\common\Noita",

        [Parameter(Position = 0, ParameterSetName = 'Default')]
        [long]
        $Seed,

        [Parameter(ParameterSetName = 'Default')]
        [switch]
        $DevMode,

        [Parameter(Mandatory, ParameterSetName = 'Unpack')]
        [switch]
        $UnpackData
    )

    $noitaArgs = @()
    $noitaFolder = $Path | Split-Path -Parent

    if ($Seed) {
        $xml = [System.Xml.XmlDocument]::new()
        $node = $xml.CreateElement('MagicNumbers')
        $xml.AppendChild($node) > $null
        $blank = $xml.CreateTextNode([Environment]::NewLine)
        $node.AppendChild($blank) > $null
        $node.SetAttribute('WORLD_SEED', $Seed)
        $node.SetAttribute('_DEBUG_DONT_LOAD_OTHER_MAGIC_NUMBERS', 1)
        $node.SetAttribute('_DEBUG_DONT_SAVE_MAGIC_NUMBERS', 1)

        $magicPath = $Path | Join-Path -ChildPath 'magic.txt'
        $sb = [System.Text.StringBuilder]::new()
        $xmlWriter = [System.Xml.XmlWriter]::Create(
            $sb,
            @{
                Indent = $true
                NewLineOnAttributes = $true
                OmitXmlDeclaration = $true
            }
        )
        $xml.Save($xmlWriter)
        $xmlText = $sb.ToString()
        Write-Verbose $xmlText
        $xmlText | Set-Content -Path $magicPath

        $noitaArgs = @(
            '-no_logo_splashes'
            '-magic_numbers', 'magic.txt'
        )
    }
    elseif ($UnpackData) {
        $noitaArgs = @(
            '-wizard_unpak'
        )
    }

    $filename = if ($DevMode) {
        'noita_dev.exe'
    }
    else {
        'noita.exe'
    }

    $executable = Join-Path $Path -ChildPath $filename

    try {
        Push-Location $Path
        & $executable @noitaArgs
    }
    finally {
        Pop-Location
    }
}

I also noticed the script is no longer working with the newer version. I made sure my installation matched the script, It was working last year, but there were a number of updates recently which are likely breaking this in the Apr 30 2024 build.

I've tried editting magic.txt manually, then setting it as read only. The contents remain, instead of resetting to WORLD_SEED="0", etc.
Noita still loads a random seed though.

Can confirm it no longer works. A pity, I wanted to be able to do this without mods.

Any update on this or does anyone have an alternative that works?

There doesn't seem to be any way I can find to do this now without mods at present. Other methods may be discovered in future, but presently I think the mods are the best bet.

There doesn't seem to be any way I can find to do this now without mods at present. Other methods may be discovered in future, but presently I think the mods are the best bet.

OK, then how do the mods accomplish it? Mean to say, the 'functionality' still exists and should be scriptable. I haven't looked at any of the seed changer mods. Which simple mod still works? I'll look at the files.

The seed changer mods are lua scripts loaded by Noita itself. It seems the magic_numbers.xml file processing feature was changed in a recent(ish) update to no longer allow setting the world seed via this mechanism.

So the only way currently that I am aware of is you must load a mod in order to force a set seed.