An example config loader node script in Godot (C#) making use of my yamlrecords project

ConfigLoader.cs

[Tool]
public partial class ConfigLoader : Node
{
    public static GameConfig Config { get; private set; }

    private string config_path;
    [Export(PropertyHint.File, hintString: "*.yml")]
    public string ConfigPath
    {
        get => config_path; set
        {
            config_path = value;
            if (!string.IsNullOrEmpty(config_path))
                TryLoad(value);
        }
    }

    private readonly List<string> errors = [];

    public override void _Ready()
    {
        if (Engine.IsEditorHint())
            return;

        if (string.IsNullOrEmpty(config_path))
            HardFail("the config file path must be set");
        else if (!TryLoad(config_path))
            HardFail("failed to load config file:\n" + string.Join('\n', errors));
    }

    private void HardFail(string message)
    {
        GD.PrintErr(message);
        GetTree().Quit(1);
    }

    private bool TryLoad(string value)
    {
        errors.Clear();
        try
        {
            using (var config_yml = FileAccess.Open(value, FileAccess.ModeFlags.Read))
                Config = YamlRecords.Deserialize<GameConfig>(config_yml.GetAsText());
            return CheckKeys();
        }
        catch (Exception ex)
        {
            errors.Add($"config parsing error: {ex.Message}");
            GD.PrintRich($"[color=red]config parsing error: {ex.Message}[color=white]");
            UpdateConfigurationWarnings();
            return false;
        }
    }

    private bool CheckKeys()
    {
        var unknown_cards = Config.StartingCards.Where(c => !Config.CardTypes.ContainsKey(c)).Distinct().ToArray();
        if (unknown_cards.Length > 0)
            errors.Add("the following starting cards do not exist in card types: " + string.Join(", ", unknown_cards));

        var unknown_flows = Config.StartingFlows.Where(c => !Config.GameFlows.ContainsKey(c)).Distinct().ToArray();
        if (unknown_flows.Length > 0)
            errors.Add("the following starting flows do not exist in game flows: " + string.Join(", ", unknown_flows));

        foreach (var flow in Config.GameFlows)
        {
            var flow_key = flow.Key;
            var flow_body = flow.Value;

            if (flow_body.States.Count == 0)
            {
                errors.Add($"flow {flow_key} has no states defined");
                continue;
            }
            if (string.IsNullOrEmpty(flow_body.StartState) && flow_body.States.Count > 1)
                errors.Add($"flow {flow_key} does not have a start state set, but has multiple states");

            foreach (var state in flow_body.States)
            {
                var state_key = state.Key;
                var state_body = state.Value;

                if (state_body.Variants.Count == 0)
                {
                    errors.Add($"state {state_key} in flow {flow_key} has no variants defined");
                    continue;
                }
                if (string.IsNullOrEmpty(state_body.DefaultVariant) && state_body.Variants.Count > 1)
                    errors.Add($"state {state_key} in flow {flow_key} does not have a default variant set, but has multiple variants");

                // todo, validate all actions
            }
        }

        if (errors.Count == 0)
            return true;

        foreach (var error in errors)
            GD.PrintRich($"[color=red]config parsing error: {error}[color=white]");
        UpdateConfigurationWarnings();
        return false;
    }

    public override string[] _GetConfigurationWarnings() => string.IsNullOrEmpty(config_path) ? ["the config file path must be set"] : [.. errors];

}