microsoft/aspire · error · ArgumentException

Chart description must be a string or a parameter resource…

Error message

Chart description must be a string or a parameter resource builder.

What it means

This error is thrown by the WithChartDescription overload accepting `object description` when the value is neither a string nor an IResourceBuilder<ParameterResource>. The Helm chart description written to Chart.yaml must be a literal string or a publish-time parameter; other types are rejected with an ArgumentException naming the `description` parameter.

Solutions

1. Pass a plain string: .WithChartDescription("My chart description")
2. Pass an IResourceBuilder<ParameterResource> from builder.AddParameter(...)
3. Convert the object value to string (or ToString()) before calling the API

Example fix

// before
object desc = GetDescription();
.WithChartDescription(desc) // throws
// after
string desc = GetDescription().ToString()!;
.WithChartDescription(desc)

public static bool IsValidChartDescriptionArg(object? d) => d is string or IResourceBuilder<ParameterResource>;

var ok = d is string || d is IResourceBuilder<ParameterResource>;

try { chart.WithChartDescription(descValue); }
catch (ArgumentException ex) when (ex.ParamName == "description") { /* use a default description or rethrow with context */ }

When it happens

Trigger: Calling WithChartDescription with an object-typed value that is not a string or IResourceBuilder<ParameterResource> — e.g. an int, bool, or a builder of the wrong resource type.

Common situations: Passing a config/JSON value typed as object without casting to string; passing an IResourceBuilder<ProjectResource> or similar instead of ParameterResource.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Chart name must be a string or a parameter resource builder.
• Cannot derive a Helm release name from resource name
• Cannot derive a Kubernetes namespace from resource name
• Chart version must be a string or a parameter resource…
• Could not parse Helm version from 'helm version --short'…

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/57f231e5c362dbad. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Kubernetes/HelmChartOptions.cs:271

        var expression = ReferenceExpression.Create($"{description.Resource}");
        EnvironmentBuilder.WithAnnotation(new HelmChartDescriptionAnnotation(expression), ResourceAnnotationMutationBehavior.Replace);
        return this;
    }

    /// <summary>
    /// Sets the Helm chart description written to the generated Chart.yaml.
    /// </summary>
    [AspireExport(MethodName = "withChartDescription")]
    internal HelmChartOptions WithChartDescription([AspireUnion(typeof(string), typeof(IResourceBuilder<ParameterResource>))] object description)
    {
        ArgumentNullException.ThrowIfNull(description);

        return description switch
        {
            string descriptionValue => WithChartDescription(descriptionValue),
            IResourceBuilder<ParameterResource> descriptionParameter => WithChartDescription(descriptionParameter),
            _ => throw new ArgumentException("Chart description must be a string or a parameter resource builder.", nameof(description))
        };
    }

    internal static void ValidateDnsLabel(string value, string target, int maxLength, string paramName)
    {
        if (value.Length > maxLength)
        {
            throw new ArgumentException($"{target} '{value}' is invalid. It must be {maxLength} characters or fewer.", paramName);
        }

        if (!DnsLabelPattern().IsMatch(value))
        {
            throw new ArgumentException($"{target} '{value}' is invalid. Use lowercase letters, numbers, and hyphens, and start and end with an alphanumeric character.", paramName);
        }
    }

    internal static void ValidateNamespace(string @namespace, string paramName)
        => ValidateDnsLabel(@namespace, "Kubernetes namespace", KubernetesNamespaceMaxLength, paramName);

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