ASP.NET Core cheat sheet

A scannable ASP.NET Core reference: 8 short snippets across 6 topics, each linking back to the lesson it came from.

At a glance

Topic	What it covers
Configuration and logging	Configuration is a flat key/value store assembled from several providers. Later providers override earlier ones, so the	lesson
Model validation and Problem Details responses	Data annotations, automatic 400 responses and a consistent error shape that a client can parse without guessing	lesson
Data access with Entity Framework Core	DbContext lifetime, migrations, loading strategies and the N+1 queries that turn a fast endpoint into a slow one	lesson
Razor Pages and MVC views	Page models group a URL's handlers with its markup, and tag helpers remove the stringly-typed parts of a view	lesson
Interactive UI with Blazor	Server, WebAssembly and hybrid differ in where the code runs. That single decision drives latency, deployment and what	lesson
Real-time features with SignalR	Hubs, groups and reconnection, and the scaling decision that has to be made before the first user connects, not after	lesson

Quick snippets

Configuration and logging

The configuration stack

{
  "Shop": {
    "PageSize": 25,
    "RetryCount": 3,
    "PricingBaseUrl": "https://pricing.internal/"
  },
  "ConnectionStrings": {
    "Default": "Data Source=shop.db"
  }
}

The configuration stack

# section separator is a double underscore
Shop__RetryCount=5 dotnet run --project src/Shop.Api

# developer secrets stay outside the repository
dotnet user-secrets init --project src/Shop.Api
dotnet user-secrets set "ConnectionStrings:Default" "Data Source=dev.db" --project src/Shop.Api

Structured logging

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "System.Net.Http.HttpClient": "Warning"
    }
  }
}

Full lesson: Configuration and logging →

Model validation and Problem Details responses

Problem Details, automatically

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "errors": {
    "Sku": ["The Sku field is required."],
    "Qty": ["The field Qty must be between 1 and 10000."]
  },
  "traceId": "00-9f2b1c4d5e6f-01"
}

Full lesson: Model validation and Problem Details responses →

Data access with Entity Framework Core

Migrations, loading and N+1

# Migrations are code: review them like code
dotnet ef migrations add AddOrderIndex --output-dir Data/Migrations
dotnet ef migrations script --idempotent -o migrate.sql
dotnet ef database update

# See the SQL a query produces, without running the app
dotnet ef dbcontext optimize --output-dir Compiled --namespace App.Compiled

Full lesson: Data access with Entity Framework Core →

Razor Pages and MVC views

Page models and handlers

<form method="post">
  <!-- The anti-forgery token is added by the form tag helper -->
  <input asp-for="Input.Note" class="form-control" />
  <span asp-validation-for="Input.Note" class="text-danger"></span>

  <button type="submit" asp-page-handler="Save">Save</button>
  <a asp-page="/Orders/Index" asp-route-id="@Model.Input.Id">Cancel</a>
</form>

@section Scripts {
  <partial name="_ValidationScriptsPartial" />
}

Full lesson: Razor Pages and MVC views →

Interactive UI with Blazor

The hosting models

// Program.cs on the server
builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents()
    .AddInteractiveWebAssemblyComponents();

var app = builder.Build();
app.MapRazorComponents<App>()
   .AddInteractiveServerRenderMode()
   .AddInteractiveWebAssemblyRenderMode();

Full lesson: Interactive UI with Blazor →

Real-time features with SignalR

Connections, reconnection and scale-out

// Scale out: without a backplane, messages only reach clients on one instance
builder.Services.AddSignalR()
    .AddStackExchangeRedis(builder.Configuration.GetConnectionString("Redis"), o =>
    {
        o.Configuration.ChannelPrefix = RedisChannel.Literal("orders");
    });

// Also raise the per-message limit when clients send large payloads
builder.Services.AddSignalR(o => o.MaximumReceiveMessageSize = 64 * 1024);

app.MapHub<OrderHub>("/hubs/orders").RequireAuthorization();

Full lesson: Real-time features with SignalR →

FAQ

Is this ASP.NET Core cheat sheet free to use?

Yes. No sign-up and no tracking: the page is static, every example is on the page itself, and you can print it or save it as a one-page reference.

Where do the examples come from?

Every snippet is taken from the 6 lessons of the ASP.NET Core course on this site, and each section links back to the lesson it was pulled from.

How do I go deeper than a cheat sheet?

Open the full ASP.NET Core course — it carries the worked explanations, the edge cases and the exercises behind every line here.

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Last refreshed 2026-09-27.