diff --git a/src/Pretzel.Logic/Extensibility/IBeforeProcessingTransform.cs b/src/Pretzel.Logic/Extensibility/IBeforeProcessingTransform.cs
new file mode 100644
index 000000000..69c055876
--- /dev/null
+++ b/src/Pretzel.Logic/Extensibility/IBeforeProcessingTransform.cs
@@ -0,0 +1,9 @@
+using System.ComponentModel.Composition;
+using Pretzel.Logic.Templating.Context;
+
+namespace Pretzel.Logic.Extensibility {
+    [InheritedExport]
+    public interface IBeforeProcessingTransform {
+        void Transform(SiteContext context);
+    }
+}
diff --git a/src/Pretzel.Logic/Pretzel.Logic.csproj b/src/Pretzel.Logic/Pretzel.Logic.csproj
index 5a6f1aba8..7a4ff334a 100644
--- a/src/Pretzel.Logic/Pretzel.Logic.csproj
+++ b/src/Pretzel.Logic/Pretzel.Logic.csproj
@@ -102,6 +102,7 @@
     <Compile Include="Extensibility\IFilter.cs" />
     <Compile Include="Extensibility\ILightweightMarkupEngine.cs" />
     <Compile Include="Extensibility\IName.cs" />
+    <Compile Include="Extensibility\IBeforeProcessingTransform.cs" />
     <Compile Include="Extensibility\ITag.cs" />
     <Compile Include="Extensibility\TagFactoryBase.cs" />
     <Compile Include="Extensions\IAssembly.cs" />
diff --git a/src/Pretzel.Logic/Templating/Context/SiteContextGenerator.cs b/src/Pretzel.Logic/Templating/Context/SiteContextGenerator.cs
index 7ce95d16b..2237185cf 100644
--- a/src/Pretzel.Logic/Templating/Context/SiteContextGenerator.cs
+++ b/src/Pretzel.Logic/Templating/Context/SiteContextGenerator.cs
@@ -7,6 +7,7 @@
 using System.IO.Abstractions;
 using System.Linq;
 using System.Text;
+using Pretzel.Logic.Extensibility;
 
 namespace Pretzel.Logic.Templating.Context
 {
@@ -21,6 +22,9 @@ public class SiteContextGenerator
         private readonly LinkHelper linkHelper;
         private readonly IConfiguration _config;
 
+        [ImportMany]
+        public IEnumerable<IBeforeProcessingTransform> BeforeProcessingTransforms;
+
         [ImportingConstructor]
         public SiteContextGenerator(IFileSystem fileSystem, LinkHelper linkHelper, IConfiguration config)
         {
@@ -58,6 +62,14 @@ public SiteContext BuildContext(string path, string destinationPath, bool includ
 
                 context.Pages = BuildPages(_config, context).ToList();
 
+                if (BeforeProcessingTransforms != null)
+                {
+                    foreach (var transform in BeforeProcessingTransforms)
+                    {
+                        transform.Transform(context);
+                    }
+                }
+
                 return context;
             }
             finally
diff --git a/src/Pretzel.Tests/Templating/Context/SiteContextGeneratorTests.cs b/src/Pretzel.Tests/Templating/Context/SiteContextGeneratorTests.cs
index 447eb78c3..4522d814e 100644
--- a/src/Pretzel.Tests/Templating/Context/SiteContextGeneratorTests.cs
+++ b/src/Pretzel.Tests/Templating/Context/SiteContextGeneratorTests.cs
@@ -11,6 +11,7 @@
 using System.Linq;
 using System.Text;
 using System.Threading;
+using Pretzel.Logic.Extensibility;
 using Xunit;
 
 namespace Pretzel.Tests.Templating.Context
@@ -1079,5 +1080,30 @@ public void permalink_is_well_formatted(string permalink, string expectedUrl, st
             var firstPost = siteContext.Posts.First();
             Assert.Equal(expectedUrl, firstPost.Url);
         }
+
+        private class BeforeProcessingTransformMock : IBeforeProcessingTransform
+        {
+            public int PostCount = 0;
+            public void Transform(SiteContext context)
+            {
+                PostCount = context.Posts.Count;
+            }
+        }
+
+        [Fact]
+        public void are_beforeprocessingtransforms_called()
+        {
+            // arrange
+            var pageTransformMock = new BeforeProcessingTransformMock();
+            generator.BeforeProcessingTransforms = new[] { pageTransformMock };
+            fileSystem.AddFile(@"C:\TestSite\_posts\2012-01-01-SomeFile.md", new MockFileData(ToPageContent("# Some File")));
+            fileSystem.AddFile(@"C:\TestSite\_posts\2012-01-01-AnotherFile.md", new MockFileData(ToPageContent("# Another File")));
+
+            // act
+            generator.BuildContext(@"C:\TestSite", @"C:\TestSite\_site", false);
+
+            // assert
+            Assert.Equal(2, pageTransformMock.PostCount);
+        }
     }
 }