What do names like d__5.MoveNext mean in a .NET stack trace?

They are types and methods the C# compiler generates. An async method or iterator becomes a state machine class named d__N, and its body runs in MoveNext, so d__5.MoveNext is your GetAsync method. Lambdas compile to b__N methods, often on a <>c or <>c__DisplayClass closure class, and local functions to g__Name|N. Since .NET Core 2.1 the runtime prints async methods by their real names, but lambdas and local functions are still shown mangled.

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.NET Stack Trace Cleaner

Paste an exception from a log. See the root cause and the line in your code that threw, with async state machines, lambdas and local functions turned back into the names you wrote.

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Exception text

fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details.
 ---> Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert duplicate key row in object 'dbo.Orders' with unique index 'IX_Orders_Number'. The duplicate key value is (SO-1042).
   at Microsoft.Data.SqlClient.SqlCommand.<>c.<ExecuteDbDataReaderAsync>b__211_0(Task`1 result)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location ---
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
ClientConnectionId:5b1e7c1a-2f0d-4a51-9c35-1f3c2e8f6a77
Error Number:2601,State:1,Class:14
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Shop.Api.Orders.OrderService.<>c__DisplayClass4_0.<<CreateAsync>g__SaveAsync|0>d.MoveNext() in /src/Shop.Api/Orders/OrderService.cs:line 58
--- End of stack trace from previous location ---
   at Shop.Api.Orders.OrderService.CreateAsync(CreateOrder request, CancellationToken ct) in /src/Shop.Api/Orders/OrderService.cs:line 41
   at Shop.Api.Orders.OrderEndpoints.<>c.<<MapOrders>b__0_1>d.MoveNext() in /src/Shop.Api/Orders/OrderEndpoints.cs:line 22
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Http.RequestDelegateFactory.<ExecuteTaskOfTargetFetchAndWriteResponse>g__ExecuteAwaited|129_0[T](Task`1 task, HttpContext httpContext, JsonTypeInfo`1 jsonTypeInfo)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

Fold framework frames Hide await/rethrow plumbing File names only Also treat as framework

Pasted from JSON logs (Application Insights, Seq, a ProblemDetails body)? Escaped \r\n sequences are unescaped automatically. Nothing is sent anywhere.

What happened

Root causeMicrosoft.Data.SqlClient.SqlException

Cannot insert duplicate key row in object 'dbo.Orders' with unique index 'IX_Orders_Number'. The duplicate key value is (SO-1042).

Your codeOrderService.CreateAsync.SaveAsyncasynclocal function — OrderService.cs:58

17 frames · 3 in your code · 4 demangled

Microsoft.EntityFrameworkCore.DbUpdateException

An error occurred while saving the entity changes. See the inner exception for details.

Shop.Api.Orders.OrderService.CreateAsync.SaveAsync()asynclocal functionOrderService.cs:58
Shop.Api.Orders.OrderService.CreateAsync(CreateOrder request, CancellationToken ct)OrderService.cs:41
Shop.Api.Orders.OrderEndpoints.MapOrders()asynclambdaOrderEndpoints.cs:22

Inner exceptionRoot causeMicrosoft.Data.SqlClient.SqlException0x80131904

Cannot insert duplicate key row in object 'dbo.Orders' with unique index 'IX_Orders_Number'. The duplicate key value is (SO-1042).

ClientConnectionId:5b1e7c1a-2f0d-4a51-9c35-1f3c2e8f6a77
Error Number:2601,State:1,Class:14

Cleaned text

The same trace in Exception.ToString() layout, ready to paste into a ticket.

exception.txt

fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details.
 ---> Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert duplicate key row in object 'dbo.Orders' with unique index 'IX_Orders_Number'. The duplicate key value is (SO-1042).
   … 4 framework frames
ClientConnectionId:5b1e7c1a-2f0d-4a51-9c35-1f3c2e8f6a77
Error Number:2601,State:1,Class:14
   --- End of inner exception stack trace ---
   … 4 framework frames
   at Shop.Api.Orders.OrderService.CreateAsync.SaveAsync() [async, local function] in OrderService.cs:line 58
   at Shop.Api.Orders.OrderService.CreateAsync(CreateOrder request, CancellationToken ct) in OrderService.cs:line 41
   at Shop.Api.Orders.OrderEndpoints.MapOrders() [async, lambda] in OrderEndpoints.cs:line 22
   … 4 framework frames

Reading compiler-generated names

C# features such as async, lambdas, iterators and local functions don't exist in IL. The compiler rewrites them into ordinary classes and methods with names you can't write yourself (they contain < and >), and those names appear in stack traces:

Name patterns

// What the compiler generates          →  What you wrote
<GetOrderAsync>d__5.MoveNext()            →  async Task GetOrderAsync()
<>c.<Main>b__0_0(Order o)                 →  o => …   (a lambda in Main, captures nothing)
<>c__DisplayClass5_0.<Find>b__0(Order o)  →  o => o.Id == id   (a lambda in Find, captures id)
<Run>g__Load|2_0()                        →  void Load() { … }   (a local function in Run)
<<Run>g__LoadAsync|2_0>d.MoveNext()       →  async Task LoadAsync()   (async local function)
Program.<Main>$(String[] args)            →  top-level statements in Program.cs
Repository`1..ctor(DbContext db)          →  the Repository<T> constructor

Why there are so many System and Microsoft frames

Every await that rethrows adds a --- End of stack trace from previous location --- line, and in .NET Framework also TaskAwaiter and ExceptionDispatchInfo frames. ASP.NET Core adds a frame for every middleware component. They're real, but rarely where the bug is. This page folds them so the frames from your own code stand out. Expand a folded group when the problem is in how you call a library.

Getting the exception text

Log the exception object rather than its Message, as in logger.LogError(ex, "Saving order {Id} failed", id): the logger then records ex.ToString(), with inner exceptions and stack traces. ex.Message alone loses both.

Frequently asked questions

What do names like <GetAsync>d__5.MoveNext mean in a .NET stack trace?

They are types and methods the C# compiler generates. An async method or iterator becomes a state machine class named <Method>d__N, and its body runs in MoveNext, so <GetAsync>d__5.MoveNext is your GetAsync method. Lambdas compile to <Method>b__N methods, often on a <>c or <>c__DisplayClass closure class, and local functions to <Method>g__Name|N. Since .NET Core 2.1 the runtime prints async methods by their real names, but lambdas and local functions are still shown mangled.

Where is the real error in an exception with inner exceptions?

Usually in the innermost one. Exception.ToString prints the outer exception first, then each inner exception after " ---> ", and the inner exception’s stack trace ends with "--- End of inner exception stack trace ---". Wrappers such as DbUpdateException, TargetInvocationException and AggregateException say what was being attempted; the innermost exception says what actually failed. In code, Exception.GetBaseException() returns it.

Is this like Ben.Demystifier?

It does a similar job on text you already have. Ben.Demystifier is a NuGet package that rewrites stack traces at run time (exception.Demystify()) using reflection, so it can also restore generic arguments, return types and tuple names. This page needs no code change or redeploy: paste a trace from a log, Application Insights or a support ticket and read it cleaned up.

Why are there no file names or line numbers in my stack trace?

Line numbers come from the PDB symbol files. If the PDBs aren’t deployed next to the assemblies, or DebugType is none, frames show only the method. Set <DebugType>portable</DebugType> or embedded in the project file and publish the .pdb files (embedded puts them inside the DLL). Release builds still have line numbers, though inlining can make them point at a caller.