dotnet/efcore · critical · InvalidOperationException

Unable to find expected assembly attribute [DesignTimeProvid

Error message

Unable to find expected assembly attribute [DesignTimeProviderServices] in provider assembly '{runtimeProviderAssemblyName}'. This attribute is required to identify the class which acts as the design-time service provider factory for the provider.

What it means

The provider assembly loaded fine, but it has no [DesignTimeProviderServices] attribute, which EF uses to locate the class that registers the provider's design-time services (scaffolding, SQL generators, etc.). This almost always means the assembly is not a real EF Core provider, or is an incompatible/old one. It is thrown as InvalidOperationException (not OperationException) because it indicates a corrupt or wrong provider rather than user input.

Source

Thrown at src/EFCore.Design/Design/Internal/DesignTimeServicesBuilder.cs:185

            }

            throw new OperationException(message, ex);
        }

        var providerServicesAttribute = providerAssembly.GetCustomAttribute<DesignTimeProviderServicesAttribute>();
        if (providerServicesAttribute == null)
        {
            var message = DesignStrings.CannotFindDesignTimeProviderAssemblyAttribute(
                provider);

            if (!throwOnError)
            {
                _reporter.WriteVerbose(message);

                return;
            }

            throw new InvalidOperationException(message);
        }

        var designTimeServicesType = providerAssembly.GetType(
            providerServicesAttribute.TypeName,
            throwOnError: true,
            ignoreCase: false)!;

        _reporter.WriteVerbose(DesignStrings.UsingProviderServices(provider));

        ConfigureDesignTimeServices(designTimeServicesType, services);
    }

    private static void ConfigureDesignTimeServices(
        Type designTimeServicesType,
        IServiceCollection services)
    {
        Check.DebugAssert(designTimeServicesType != null, "designTimeServicesType is null.");

View on GitHub (pinned to dbf9771522)

Solutions

Verify the package is an EF Core provider: install the official Microsoft.EntityFrameworkCore.<Provider> package.
If using a custom/community provider, ensure its assembly is decorated with [DesignTimeProviderServices(typeof(...))] and that the design-time services type exists.
Upgrade the provider to a version that matches your EF Core runtime version.
Remove any stray Use* call that references a non-provider assembly.

Example fix

// before: wrong package
options.UseSqlServer(connection); // but only System.Data.SqlClient referenced
// after
// dotnet add package Microsoft.EntityFrameworkCore.SqlServer
options.UseSqlServer(connection);

Defensive patterns

Strategy: validation

Validate before calling

var attr = Assembly.Load(providerAssemblyName)
    .GetCustomAttribute<DesignTimeProviderServicesAttribute>();
if (attr is null) throw new InvalidOperationException($"'{providerAssemblyName}' is not an EF Core provider (missing DesignTimeProviderServices attribute).");

Prevention

Use only official Microsoft.EntityFrameworkCore.<Provider> packages.
For custom providers, always decorate the assembly with [DesignTimeProviderServices].
Run a smoke-test that loads the provider and checks for the attribute.

When it happens

Trigger: ConfigureProviderServices succeeds in loading the assembly (line 156) but providerAssembly.GetCustomAttribute<DesignTimeProviderServicesAttribute>() returns null at line 172. Happens when UseSqlServer points at a plain library, a hand-rolled provider lacking the attribute, or a provider built against a different EF Core design API.

Common situations: Pointing Use*[provider] at an ADO.NET driver instead of the EF provider (e.g. System.Data.SqlClient vs Microsoft.EntityFrameworkCore.SqlServer); using a community provider that dropped design-time support; a custom provider whose DesignTimeProviderServicesAttribute was removed in a refactor.

Related errors

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/a8b35de2bfdda075. Report an issue: GitHub.