Build a CMS in C#

Quickstart

Install the engine plus one storage adapter. While Klassd is in beta the packages are prerelease:

dotnet add package Klassd.Backoffice --prerelease
dotnet add package Klassd.Data.Sqlite --prerelease

1. Define content types

Any class deriving from PageBase or BlockBase in your app is discovered automatically:

using Klassd.Core.Abstractions;

[CmsPage(DefaultSlug = "", Icon = "house")]
[AllowedChildren(typeof(ArticlePage))]
public class HomePage : PageBase
{
    [Localized]                          // separate value per locale
    public string Title { get; set; } = "";
    public string SubTitle { get; set; } = "";
    public BlockArea HeroBlocks { get; set; } = new();
}

public class ArticlePage : PageBase
{
    public string Title { get; set; } = "";

    [CmsField(FieldType = "textarea")]
    public string Body { get; set; } = "";

    public MediaReference Hero { get; set; } = new();

    [AllowedRelations(typeof(ArticlePage))]
    public PageReference Related { get; set; } = new();
}

2. Wire it up in Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddKlassd(builder.Configuration)                       // discovers your content types
    .UseSqlite(builder.Configuration.GetSection("Sqlite"))  // or .UseMongoDb / .UsePostgres
    .UseInMemoryCache();                                    // optional read-through cache

var app = builder.Build();
app.UseKlassd();   // auth + antiforgery + seed/init + static assets + /api + Blazor admin
app.Run();

Host .csproj: a host with no .razor files of its own must set <RequiresAspNetWebAssets>true</RequiresAspNetWebAssets>, or /admin 404s on blazor.web.js. (If your host already has .razor files the SDK turns this on for you.)

3. Run

Open /admin to author content. Your frontend reads published content from /api/pages.

Content types

• Pages — derive from PageBase. Live in a tree (parent/child), have a slug, and are delivered at /api/pages.
• Blocks — derive from BlockBase. Reusable content components placed into a page's BlockArea properties; each can be scheduled with a publish window.
• Globals — annotate with [CmsGlobal]. Singletons for site chrome (header, footer) — exactly what this website uses.

Every public property becomes an editable field. The editor for a field is chosen from its CLR type (see below) or an explicit [CmsField(FieldType = "…")].

Built-in property types

Each field maps to a property type by its CLR type, or you can force one with [CmsField(FieldType = "alias")].

public string Title { get; set; } = "";

[CmsField(FieldType = "textarea")]
public string Body { get; set; } = "";

public int Order { get; set; }

public bool Featured { get; set; }

public DateTime PublishedAt { get; set; }

public BlockArea PageBlocks { get; set; } = new();

public MediaReference Image { get; set; } = new();

[AllowedRelations(typeof(ArticlePage))]
public PageReference Related { get; set; } = new();

[CmsField(FieldType = "richtext")]
public string Body { get; set; } = "";

[CmsField(FieldType = "email")]
public string Contact { get; set; } = "";

public decimal Price { get; set; }

public DateOnly Released { get; set; }

Media options

Media is organised into named sections, each backed by its own blob adapter (FileSystem / S3 / Google Cloud). Configure with .AddMedia(...):

• UseFileSystem(path) / UseS3(...) / UseGoogleCloudStorage(...) — pick a backend per section.
• AllowContentTypes("image/*", "application/pdf") — restrict uploads.
• ResizeImages(maxEdgePixels) — downscale in the browser before upload.
• Breakpoints("default", "mobile", "tablet") — focal-point editors the admin offers.

Relationship options

• Declare a PageReference property (or [CmsField(FieldType = "relationship")] on a string).
• [AllowedRelations(typeof(ArticlePage), …)] — restrict which page types appear in the picker. Omit for any type.
• Stores the target's ContentId (locale-agnostic) — resolve from the frontend via GET /api/pages/content/{contentId}, then pick the translation for the locale you're rendering.

Attributes reference

Editorial features

Beyond the content model, the engine ships the workflow features editors expect:

Extending Klassd

Custom property editors

A custom field editor is a single Blazor component — no JS, no registration. Inherit PropertyEditorBase and mark it with [PropertyEditor("alias")]; the engine discovers it by assembly scan and synthesises the property type for you.

@attribute [PropertyEditor("color")]
@inherits PropertyEditorBase

<input type="color" value="@Value"
       @oninput="e => SetValueAsync(e.Value?.ToString() ?? string.Empty)" />

Then reference the alias from any field:

[CmsField(FieldType = "color")]
public string BackgroundColor { get; set; } = "";

PropertyEditorBase gives you Value (string), ValueChanged and the field metadata. The stored value is always a string — content is persisted DB-agnostically — and MediaReference / PageReference are typed wrappers over that string.

Custom storage & media adapters

Storage and media backends are swappable. The engine depends only on interfaces in Klassd.Abstractions — never a concrete database or cloud SDK. Implement IPageStore / IMediaStore (storage) or IBlobStore (media) and add a UseXxx registration extension. Worked examples ship in the examples/ folder.

Delivery API

The headless GET endpoints are anonymous so a public frontend can read published content (this site consumes them):

• GET /api/pages — all pages for a locale (?locale=en).
• GET /api/pages/{id} — a single page.
• GET /api/pages/by-slug/{**slug} — a page by its slug (?locale=en).
• GET /api/pages/content/{contentId} — a page and its translations (resolve relationships here).
• GET /api/pages/{id}/translations — every locale of one page.
• GET /api/globals/{name} — a global singleton (e.g. SiteHeader).
• GET /api/media/{id} — a media item's bytes.

Only published, in-window content is delivered. Single-page GETs accept ?depth=1 to resolve PageReference/MediaReference fields to URLs and ?expand= to pick which. Scheduling resolves per request; ?preview=<utc> time-travels delivery when enabled. A /graphql endpoint is available via the opt-in GraphQL package.

API referenceView on GitHubAll NuGet packages

Packages

Install the engine plus the adapters you need — each keeps its SDK isolated, so you only pull in what you wire up. While Klassd is in beta, add --prerelease.

All packages on NuGet

Klassd vs Umbraco vs Payload

How Klassd's code-first, .NET-native approach compares to two popular headless CMSs. All three are open-source (MIT).

Klassd's niche: true code-first content modelling in C#, a Blazor admin with no JS build step, and pluggable storage — shipped as NuGet packages you compose. Comparison reflects each project's core/open-source offering as of 2026.