Render Preview API

What problem this solves

Many platforms need a preview endpoint: users choose a chart and values, then the product shows the manifest before anything touches the cluster.

Packages to install

dotnet add package HelmSharp.Chart --version 1.1.0
dotnet add package HelmSharp.Engine --version 1.1.0

Minimal complete code

app.MapPost("/preview", async (
    PreviewRequest request,
    CancellationToken cancellationToken) =>
{
    var chart = await HelmChartLoader.LoadAsync(request.ChartPath, cancellationToken);
    var values = await HelmValues.BuildAsync(
        chart,
        request.ValuesFiles,
        request.ValuesContent,
        request.SetValues,
        setFileValues: null,
        request.SetStringValues,
        request.SetJsonValues,
        cancellationToken);

    var renderer = new HelmTemplateRenderer(
        chart,
        request.ReleaseName,
        request.Namespace,
        values,
        kubeVersion: request.KubeVersion,
        apiVersions: request.ApiVersions);

    return Results.Text(renderer.Render(), "text/yaml");
});

Why these APIs

This example avoids HelmClient because preview APIs usually should not own release state. The lower-level path makes it clear that the endpoint loads, merges, and renders only.

Production notes

• Validate chart paths against an allowlist or internal chart registry.
• Store the values inputs used for each preview so later apply actions are reproducible.
• Add size limits for uploaded values content.

Next step

Pair this with Dry-run Deployment when the preview can become a release.