Blazor.WhyDidYouRender 3.3.0

Blazor.WhyDidYouRender

👁 NuGet
👁 License: LGPL v3

A powerful cross-platform performance monitoring and debugging tool for Blazor applications (Server, WebAssembly, SSR) that helps identify unnecessary re-renders and optimize component performance. Inspired by the React why-did-you-render library.

🌟 Features

• Cross-Platform Support: Works with Blazor Server, WebAssembly, and SSR
• Render Tracking: Monitor when and why components re-render
• Parameter Change Detection: Identify which parameter changes trigger re-renders
• State Tracking: Field-level change detection with [TrackState] and [IgnoreState] attributes
• Unnecessary Render Detection: Automatically detect and flag unnecessary re-renders
• Performance Metrics: Track render duration and frequency
• OpenTelemetry/Aspire Integration: Optional structured logs, traces, and metrics for observability dashboards
• Browser Console Logging: Rich logging output in browser developer tools

📦 Installation

dotnet add package Blazor.WhyDidYouRender

🚀 Quick Start

1. Register Services

using Blazor.WhyDidYouRender.Extensions;

builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = builder.Environment.IsDevelopment();
 config.Verbosity = TrackingVerbosity.Normal;
 config.Output = TrackingOutput.Both;
 config.TrackParameterChanges = true;
 config.EnableStateTracking = true;
});

2. Initialize Services

var app = builder.Build();

// For Server/SSR
app.Services.InitializeSSRServices();

3. Initialize Browser Logging (Required for Console Output)

In a component that runs after JavaScript is available (e.g., MainLayout.razor or App.razor):

@inject IServiceProvider ServiceProvider
@inject IJSRuntime JSRuntime

@code {
 protected override async Task OnAfterRenderAsync(bool firstRender)
 {
 if (firstRender)
 {
 await ServiceProvider.InitializeWhyDidYouRenderAsync(JSRuntime);
 }
 }
}

Note: This step is required to see output in the browser's developer console. Without it, browser console logging won't work.

4. Track Components

@using Blazor.WhyDidYouRender.Components
@inherits TrackedComponentBase

<h1>Counter</h1>
<p>Count: @currentCount</p>

@code {
 private int currentCount = 0; // Auto-tracked
}

📡 .NET Aspire / OpenTelemetry Integration

Enable rich observability with the Aspire dashboard:

// Add Aspire service defaults
builder.AddServiceDefaults();

builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = true;
 config.EnableOpenTelemetry = true;
 config.EnableOtelLogs = true;
 config.EnableOtelTraces = true;
 config.EnableOtelMetrics = true;
});

What you'll see in Aspire:

• Traces: WhyDidYouRender.Render spans with wdyrl.* attributes
• Metrics: wdyrl.renders, wdyrl.rerenders.unnecessary, wdyrl.render.duration.ms
• Structured Logs: Correlated to traces via Activity.Current

See for detailed setup and troubleshooting.

📚 Documentation

• - Step-by-step setup for different scenarios
• - All configuration options explained
• - Complete API reference
• - Upgrading from previous versions
• - Usage patterns and optimization tips
• - Aspire/OpenTelemetry setup

🎯 Integration Scenarios

Scenario 1: New Blazor Server App

Step 1: Create New Project

dotnet new blazorserver -n MyBlazorApp
cd MyBlazorApp

Step 2: Install Package

dotnet add package Blazor.WhyDidYouRender

Step 3: Configure Services

Update Program.cs:

using Blazor.WhyDidYouRender.Extensions;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();
builder.Services.AddServerSideBlazor();

// Add WhyDidYouRender
builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = builder.Environment.IsDevelopment();
 config.Verbosity = TrackingVerbosity.Normal;
 config.Output = TrackingOutput.Both;
 config.TrackParameterChanges = true;
 config.TrackPerformance = true;
});

var app = builder.Build();

// Initialize WhyDidYouRender SSR services
app.Services.InitializeSSRServices();

if (!app.Environment.IsDevelopment())
{
 app.UseExceptionHandler("/Error");
 app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();

app.MapRazorPages();
app.MapBlazorHub();
app.MapFallbackToPage("/_Host");

app.Run();

Optional: Enable .NET Aspire / OpenTelemetry

// Add Aspire service defaults
builder.AddServiceDefaults();

builder.Services.AddWhyDidYouRender(config =>
{
 config.EnableOpenTelemetry = true;
 config.EnableOtelLogs = true;
 config.EnableOtelTraces = true;
 config.EnableOtelMetrics = true;
});

See for verification steps and troubleshooting.

Step 4: Update Components

Update Pages/Counter.razor:

@page "/counter"
@using Blazor.WhyDidYouRender.Components
@using Blazor.WhyDidYouRender.Extensions
@inherits TrackedComponentBase
@inject IJSRuntime JSRuntime
@inject IServiceProvider ServiceProvider

<PageTitle>Counter</PageTitle>

<h1>Counter</h1>

<p role="status">Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
 private int currentCount = 0;
 private bool browserLoggerInitialized = false;

 protected override async Task OnAfterRenderAsync(bool firstRender)
 {
 if (firstRender && !browserLoggerInitialized)
 {
 // Initialize WhyDidYouRender browser logging
 await ServiceProvider.InitializeWhyDidYouRenderAsync(JSRuntime);
 browserLoggerInitialized = true;
 }
 await base.OnAfterRenderAsync(firstRender);
 }

 private void IncrementCount()
 {
 currentCount++;
 }
}

Scenario 2: Existing Blazor Server App

Step 1: Install Package

dotnet add package Blazor.WhyDidYouRender

Step 2: Add Service Registration

In your existing Program.cs, add the service registration:

// Add this after your existing service registrations
builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = builder.Environment.IsDevelopment();
 config.Verbosity = TrackingVerbosity.Normal;
 config.Output = TrackingOutput.Both;
 config.TrackParameterChanges = true;
});

Step 3: Gradually Migrate Components

Start with components you want to optimize:

// Before
@inherits ComponentBase

// After
@using Blazor.WhyDidYouRender.Components
@inherits TrackedComponentBase

Scenario 3: Blazor WebAssembly App

Step 1: Install Package

dotnet add package Blazor.WhyDidYouRender

Step 2: Configure Services

Update Program.cs:

using Microsoft.AspNetCore.Components.Web;
using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using Blazor.WhyDidYouRender.Extensions;

var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");

builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });

// Add WhyDidYouRender
builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = builder.HostEnvironment.IsDevelopment();
 config.Verbosity = TrackingVerbosity.Normal;
 config.Output = TrackingOutput.BrowserConsole; // WebAssembly only supports browser console
 config.TrackParameterChanges = true;
 config.TrackPerformance = true;
});

await builder.Build().RunAsync();

⚙️ Configuration Examples

Development Configuration

builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = true;
 config.Verbosity = TrackingVerbosity.Verbose;
 config.Output = TrackingOutput.Both;
 config.TrackParameterChanges = true;
 config.TrackPerformance = true;
 config.IncludeSessionInfo = true;
});

Production Configuration

builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = false; // Disable in production
});

Staging Configuration

builder.Services.AddWhyDidYouRender(config =>
{
 config.Enabled = true;
 config.Verbosity = TrackingVerbosity.Minimal;
 config.Output = TrackingOutput.Console;
 config.TrackPerformance = true;
});

🔧 Advanced Integration

Custom Configuration Provider

public class WhyDidYouRenderConfigProvider
{
 public static WhyDidYouRenderConfig GetConfiguration(IWebHostEnvironment env)
 {
 return new WhyDidYouRenderConfig
 {
 Enabled = env.IsDevelopment() || env.IsStaging(),
 Verbosity = env.IsDevelopment() ? TrackingVerbosity.Verbose : TrackingVerbosity.Normal,
 Output = env.IsDevelopment() ? TrackingOutput.Both : TrackingOutput.Console,
 TrackParameterChanges = true,
 TrackPerformance = true,
 IncludeSessionInfo = env.IsDevelopment()
 };
 }
}

// Usage in Program.cs
builder.Services.AddWhyDidYouRender(
 WhyDidYouRenderConfigProvider.GetConfiguration(builder.Environment)
);

Conditional Component Tracking

@using Blazor.WhyDidYouRender.Components

@if (ShouldTrack)
{
 @inherits TrackedComponentBase
}
else
{
 @inherits ComponentBase
}

@code {
 private bool ShouldTrack =>
 Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Development";
}

Browser logging initialization (explicit)

In interactive rendering or when using browser console logging, initialize WhyDidYouRender once JS is available (e.g., in MainLayout):

@inherits LayoutComponentBase
@inject IServiceProvider ServiceProvider
@inject IJSRuntime JSRuntime

@code {
 protected override async Task OnAfterRenderAsync(bool firstRender)
 {
 if (firstRender)
 {
 await ServiceProvider.InitializeAsync(JSRuntime);
 }
 }
}

Notes:

• WASM: You can alternatively call await host.Services.InitializeWasmAsync(jsRuntime) in Program.cs; the component-based init above also works.
• Server/SSR (interactive) with browser console: explicit InitializeAsync(JSRuntime) prevents timing errors on first paint.
• Server-only logging: set config.Output = TrackingOutput.Console to disable browser console output.

🎨 Component Migration Patterns

Pattern 1: Gradual Migration

Start with high-traffic or problematic components:

// Identify components with performance issues first
@inherits TrackedComponentBase // Add to specific components

Pattern 2: Base Component Approach

Create a custom base component:

// Create MyTrackedComponentBase.cs
public abstract class MyTrackedComponentBase : TrackedComponentBase
{
 // Add your common component logic here
}

// Use in components
@inherits MyTrackedComponentBase

Pattern 3: Conditional Tracking

Use preprocessor directives for conditional tracking:

#if DEBUG
@using Blazor.WhyDidYouRender.Components
@inherits TrackedComponentBase
#else
@inherits ComponentBase
#endif

Pattern 4: Use RenderTrackerService Directly

@inject RenderTrackerService RenderTracker

@code {
 protected override void OnAfterRender(bool firstRender)
 {
 RenderTracker.TrackRender(this, "OnAfterRender", firstRender);
 base.OnAfterRender(firstRender);
 }
}

🚨 Common Issues & Solutions

Issue 1: Service Not Registered

Error: InvalidOperationException: Unable to resolve service for type 'RenderTrackerService'

Solution: Ensure you've called AddWhyDidYouRender() in your service registration:

builder.Services.AddWhyDidYouRender();

Issue 2: No Console Output

Problem: Not seeing any tracking information in browser console.

Solutions:

1. Check that tracking is enabled: config.Enabled = true
2. Verify output is set to browser: config.Output = TrackingOutput.Both
3. Ensure components inherit from TrackedComponentBase
4. Initialize browser logging: await ServiceProvider.InitializeWhyDidYouRenderAsync(JSRuntime)
5. Open browser developer tools console

Issue 3: Too Much Logging

Problem: Console is flooded with tracking information.

Solutions:

1. Reduce verbosity: config.Verbosity = TrackingVerbosity.Minimal
2. Disable parameter tracking: config.TrackParameterChanges = false
3. Disable in production: config.Enabled = Environment.IsDevelopment()

Issue 4: Performance Impact

Problem: Tracking is affecting application performance.

Solutions:

1. Disable in production environments
2. Use selective component tracking
3. Adjust tracking granularity
4. Consider enabling .NET Aspire/OpenTelemetry for server-side observability

📊 Monitoring & Debugging

Browser Console Usage

1. Open Developer Tools (F12)
2. Navigate to Console tab
3. Look for [WhyDidYouRender] messages
4. Use console filters to focus on specific components

🔄 Migration Checklist

• Install Blazor.WhyDidYouRender package
• Add service registration in Program.cs
• Configure environment-specific settings
• Update target components to inherit from TrackedComponentBase
• Test in development environment
• Verify console output
• Configure for staging/production environments
• Document component tracking decisions
• Train team on usage and interpretation

📚 Next Steps

After successful integration:

1. Monitor component render patterns
2. Identify unnecessary re-renders
3. Optimize component parameters and state management
4. Use insights to improve application performance
5. Consider enabling .NET Aspire/OpenTelemetry for ongoing monitoring

📄 License

This project is licensed under the GNU Lesser General Public License v3.0 (LGPL-3.0) - see the file for details.

🤝 Contributing

Contributions are welcome! Please see for guidelines.

📋 Changelog

See for a list of changes and version history.