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docs(dotnet): add Web.config DSN example for ASP.NET #15876

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13 changes: 12 additions & 1 deletion docs/platforms/dotnet/guides/aspnet/index.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -33,9 +33,20 @@ as well as your logs as breadcrumbs. The logging integrations also capture event

You configure the SDK in the `Global.asax.cs`:

If you'd prefer not to hardcode your DSN in your source code, you can store it in your `Web.config` file:

```xml {filename:Web.config}
<configuration>
<appSettings>
<add key="SentryDsn" value="___PUBLIC_DSN___" />
</appSettings>
</configuration>
```


```csharp
using System;
using System.Configuration;
using System.Web;
using Sentry.AspNet;
using Sentry.EntityFramework; // If you also installed Sentry.EntityFramework
Expand All @@ -50,7 +61,7 @@ public class MvcApplication : HttpApplication
// Initialize Sentry to capture AppDomain unhandled exceptions and more.
_sentry = SentrySdk.Init(options =>
{
options.Dsn = "___PUBLIC_DSN___";
options.Dsn = ConfigurationManager.AppSettings["SentryDsn"];
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@sentry sentry bot Dec 19, 2025

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Bug: The documentation's code example for ASP.NET will crash the application on startup if the SentryDsn key is missing from Web.config due to an unhandled ArgumentNullException.
Severity: CRITICAL | Confidence: High

🔍 Detailed Analysis

The code example in the documentation for ASP.NET initialization uses options.Dsn = ConfigurationManager.AppSettings["SentryDsn"];. If the SentryDsn key is missing from Web.config, ConfigurationManager.AppSettings returns null. In Sentry SDK 4.0+, passing a null DSN to SentrySdk.Init() throws an ArgumentNullException. Because this initialization code is placed in Application_Start(), the unhandled exception will prevent the application from starting. The documentation fails to warn users that this configuration key is mandatory, making it easy for a developer following the guide to cause a startup crash.

💡 Suggested Fix

Update the documentation to include a prominent warning that the SentryDsn key in Web.config is mandatory. Alternatively, modify the code example to include null-checking before assigning the DSN to options.Dsn to prevent the SentrySdk.Init() call from throwing an exception if the key is not found.

🤖 Prompt for AI Agent 
Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: docs/platforms/dotnet/guides/aspnet/index.mdx#L64

Potential issue: The code example in the documentation for ASP.NET initialization uses
`options.Dsn = ConfigurationManager.AppSettings["SentryDsn"];`. If the `SentryDsn` key
is missing from `Web.config`, `ConfigurationManager.AppSettings` returns `null`. In
Sentry SDK 4.0+, passing a `null` DSN to `SentrySdk.Init()` throws an
`ArgumentNullException`. Because this initialization code is placed in
`Application_Start()`, the unhandled exception will prevent the application from
starting. The documentation fails to warn users that this configuration key is
mandatory, making it easy for a developer following the guide to cause a startup crash.

Did we get this right? 👍 / 👎 to inform future reviews.
Reference ID: 7752030

// When configuring for the first time, to see what the SDK is doing:
options.Debug = true;
// Adds request URL and headers, IP and name for users, etc.
Expand Down