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title author description monikerRange ms.author ms.custom ms.date uid
Control head content in ASP.NET Core Blazor apps
guardrex
Learn how to control head content in Blazor apps, including how to set the page title from a component.
>= aspnetcore-6.0
riande
mvc
11/08/2022
blazor/components/control-head-content

Control <head> content in ASP.NET Core Blazor apps

[!INCLUDE]

Razor components can modify the HTML <head> element content of a page, including setting the page's title (<title> element) and modifying metadata (<meta> elements).

Control <head> content in a Razor component

Specify the page's title with the xref:Microsoft.AspNetCore.Components.Web.PageTitle component, which enables rendering an HTML <title> element to a HeadOutlet component.

Specify <head> element content with the xref:Microsoft.AspNetCore.Components.Web.HeadContent component, which provides content to a HeadOutlet component.

The following example sets the page's title and description using Razor.

Pages/ControlHeadContent.razor:

:::moniker range=">= aspnetcore-7.0"

:::code language="razor" source="~/../blazor-samples/7.0/BlazorSample_WebAssembly/Pages/control-head-content/ControlHeadContent.razor" highlight="13,15-17":::

:::moniker-end

:::moniker range="< aspnetcore-7.0"

:::code language="razor" source="~/../blazor-samples/6.0/BlazorSample_WebAssembly/Pages/control-head-content/ControlHeadContent.razor" highlight="13,15-17":::

:::moniker-end

:::moniker range="< aspnetcore-7.0"

Control <head> content during prerendering

This section applies to prerendered Blazor WebAssembly apps and Blazor Server apps.

When Razor components are prerendered, the use of a layout page (_Layout.cshtml) is required to control <head> content with the xref:Microsoft.AspNetCore.Components.Web.PageTitle and xref:Microsoft.AspNetCore.Components.Web.HeadContent components. The reason for this requirement is that components that control <head> content must be rendered before the layout with the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component. This order of rendering is required to control head content.

If the shared _Layout.cshtml file doesn't have a Component Tag Helper for a xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component, add it to the <head> elements.

In a required, shared _Layout.cshtml file of a Blazor Server app or Razor Pages/MVC app that embeds components into pages or views:

<component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />

In a required, shared _Layout.cshtml file of a prerendered hosted Blazor WebAssembly app:

<component type="typeof(HeadOutlet)" render-mode="WebAssemblyPrerendered" />

:::moniker-end

HeadOutlet component

The xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component renders content provided by xref:Microsoft.AspNetCore.Components.Web.PageTitle and xref:Microsoft.AspNetCore.Components.Web.HeadContent components.

:::moniker range=">= aspnetcore-8.0"

In a Blazor Web App created from the project template, the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component in App.razor renders <head> content:

<head>
    ...
    <HeadOutlet />
</head>

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

In Blazor Server apps created from the Blazor Server project template, a Component Tag Helper renders <head> content for the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component in Pages/_Host.cshtml:

<head>
    ...
    <component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />
</head>

:::moniker-end

:::moniker range="< aspnetcore-7.0"

In Blazor Server apps created from the Blazor Server project template, a Component Tag Helper renders <head> content for the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component in Pages/_Layout.cshtml:

<head>
    ...
    <component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />
</head>

:::moniker-end

In an app created from the Blazor WebAssembly project template, the xref:Microsoft.AspNetCore.Components.Web.HeadOutlet component is added to the xref:Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder.RootComponents collection of the xref:Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder in Program.cs:

builder.RootComponents.Add<HeadOutlet>("head::after");

When the ::after pseudo-selector is specified, the contents of the root component are appended to the existing head contents instead of replacing the content. This allows the app to retain static head content in wwwroot/index.html without having to repeat the content in the app's Razor components.

Not found page title

In Blazor apps created from Blazor project templates, the NotFound component template in the App component (App.razor) sets the page title to Not found.

App.razor:

<PageTitle>Not found</PageTitle>

Additional resources

Mozilla MDN Web Docs documentation: