diff --git a/csharp/extractor/Semmle.Extraction.CIL.Driver/Program.cs b/csharp/extractor/Semmle.Extraction.CIL.Driver/Program.cs
index 53542c970e9..940cd647ed8 100644
--- a/csharp/extractor/Semmle.Extraction.CIL.Driver/Program.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL.Driver/Program.cs
@@ -24,7 +24,7 @@ namespace Semmle.Extraction.CIL.Driver
         {
             var sw = new Stopwatch();
             sw.Start();
-            Entities.Assembly.ExtractCIL(layout, assemblyPath, logger, nocache, extractPdbs, trapCompression, out _, out _);
+            Analyser.ExtractCIL(layout, assemblyPath, logger, nocache, extractPdbs, trapCompression, out _, out _);
             sw.Stop();
             logger.Log(Severity.Info, "  {0} ({1})", assemblyPath, sw.Elapsed);
         }
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Analyser.cs b/csharp/extractor/Semmle.Extraction.CIL/Analyser.cs
new file mode 100644
index 00000000000..dee801cc171
--- /dev/null
+++ b/csharp/extractor/Semmle.Extraction.CIL/Analyser.cs
@@ -0,0 +1,53 @@
+using Semmle.Util.Logging;
+using System;
+using Semmle.Util;
+using Semmle.Extraction.CIL.Entities;
+
+namespace Semmle.Extraction.CIL
+{
+    public static class Analyser
+    {
+        private static void ExtractCIL(Extractor extractor, TrapWriter trapWriter, bool extractPdbs)
+        {
+            using var cilContext = new Context(extractor, trapWriter, extractor.OutputPath, extractPdbs);
+            cilContext.Populate(new Assembly(cilContext));
+            cilContext.PopulateAll();
+        }
+
+        /// <summary>
+        /// Main entry point to the CIL extractor.
+        /// Call this to extract a given assembly.
+        /// </summary>
+        /// <param name="layout">The trap layout.</param>
+        /// <param name="assemblyPath">The full path of the assembly to extract.</param>
+        /// <param name="logger">The logger.</param>
+        /// <param name="nocache">True to overwrite existing trap file.</param>
+        /// <param name="extractPdbs">Whether to extract PDBs.</param>
+        /// <param name="trapFile">The path of the trap file.</param>
+        /// <param name="extracted">Whether the file was extracted (false=cached).</param>
+        public static void ExtractCIL(Layout layout, string assemblyPath, ILogger logger, bool nocache, bool extractPdbs, TrapWriter.CompressionMode trapCompression, out string trapFile, out bool extracted)
+        {
+            trapFile = "";
+            extracted = false;
+            try
+            {
+                var canonicalPathCache = CanonicalPathCache.Create(logger, 1000);
+                var pathTransformer = new PathTransformer(canonicalPathCache);
+                var extractor = new Extractor(false, assemblyPath, logger, pathTransformer);
+                var transformedAssemblyPath = pathTransformer.Transform(assemblyPath);
+                var project = layout.LookupProjectOrDefault(transformedAssemblyPath);
+                using var trapWriter = project.CreateTrapWriter(logger, transformedAssemblyPath.WithSuffix(".cil"), trapCompression, discardDuplicates: true);
+                trapFile = trapWriter.TrapFile;
+                if (nocache || !System.IO.File.Exists(trapFile))
+                {
+                    ExtractCIL(extractor, trapWriter, extractPdbs);
+                    extracted = true;
+                }
+            }
+            catch (Exception ex)  // lgtm[cs/catch-of-all-exceptions]
+            {
+                logger.Log(Severity.Error, string.Format("Exception extracting {0}: {1}", assemblyPath, ex));
+            }
+        }
+    }
+}
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Context.Factories.cs b/csharp/extractor/Semmle.Extraction.CIL/Context.Factories.cs
index 1017b2f1a19..65c72487b65 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Context.Factories.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Context.Factories.cs
@@ -9,11 +9,11 @@ namespace Semmle.Extraction.CIL
     /// <summary>
     /// Provides methods for creating and caching various entities.
     /// </summary>
-    public sealed partial class Context
+    internal sealed partial class Context
     {
         private readonly Dictionary<object, Label> ids = new Dictionary<object, Label>();
 
-        public T Populate<T>(T e) where T : IExtractedEntity
+        internal T Populate<T>(T e) where T : IExtractedEntity
         {
             if (e.Label.Valid)
             {
@@ -28,7 +28,7 @@ namespace Semmle.Extraction.CIL
             else
             {
                 e.Label = GetNewLabel();
-                DefineLabel(e, TrapWriter.Writer, Extractor);
+                DefineLabel(e);
                 ids.Add(e, e.Label);
                 PopulateLater(() =>
                 {
@@ -76,7 +76,7 @@ namespace Semmle.Extraction.CIL
                 {
                     Label = GetNewLabel()
                 };
-                DefineLabel(e, TrapWriter.Writer, Extractor);
+                DefineLabel(e);
                 primitiveTypes[(int)code] = e;
             }
 
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Context.cs b/csharp/extractor/Semmle.Extraction.CIL/Context.cs
index a0d6ad1ab6f..acb66dc3284 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Context.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Context.cs
@@ -10,7 +10,7 @@ namespace Semmle.Extraction.CIL
     /// Adds additional context that is specific for CIL extraction.
     /// One context = one DLL/EXE.
     /// </summary>
-    public sealed partial class Context : Extraction.Context, IDisposable
+    internal sealed partial class Context : Extraction.Context, IDisposable
     {
         private readonly FileStream stream;
         private Entities.Assembly? assemblyNull;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/EmptyContext.cs b/csharp/extractor/Semmle.Extraction.CIL/EmptyContext.cs
index 1105bc39cba..d5344877264 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/EmptyContext.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/EmptyContext.cs
@@ -5,7 +5,7 @@ namespace Semmle.Extraction.CIL
     /// <summary>
     /// A generic context which does not contain any type parameters.
     /// </summary>
-    public class EmptyContext : IGenericContext
+    internal class EmptyContext : IGenericContext
     {
         public EmptyContext(Context cx)
         {
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Assembly.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Assembly.cs
index feff55836c0..2191afef125 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Assembly.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Assembly.cs
@@ -1,18 +1,15 @@
 using System.Reflection;
 using System.Globalization;
 using System.Collections.Generic;
-using Semmle.Util.Logging;
-using System;
 using Semmle.Extraction.Entities;
 using System.IO;
-using Semmle.Util;
 
 namespace Semmle.Extraction.CIL.Entities
 {
     /// <summary>
     /// An assembly to extract.
     /// </summary>
-    public class Assembly : LabelledEntity, ILocation
+    internal class Assembly : LabelledEntity, ILocation
     {
         private readonly File file;
         private readonly AssemblyName assemblyName;
@@ -101,48 +98,5 @@ namespace Semmle.Extraction.CIL.Entities
                 }
             }
         }
-
-        private static void ExtractCIL(Extractor extractor, TrapWriter trapWriter, bool extractPdbs)
-        {
-            using var cilContext = new Context(extractor, trapWriter, extractor.OutputPath, extractPdbs);
-            cilContext.Populate(new Assembly(cilContext));
-            cilContext.PopulateAll();
-        }
-
-        /// <summary>
-        /// Main entry point to the CIL extractor.
-        /// Call this to extract a given assembly.
-        /// </summary>
-        /// <param name="layout">The trap layout.</param>
-        /// <param name="assemblyPath">The full path of the assembly to extract.</param>
-        /// <param name="logger">The logger.</param>
-        /// <param name="nocache">True to overwrite existing trap file.</param>
-        /// <param name="extractPdbs">Whether to extract PDBs.</param>
-        /// <param name="trapFile">The path of the trap file.</param>
-        /// <param name="extracted">Whether the file was extracted (false=cached).</param>
-        public static void ExtractCIL(Layout layout, string assemblyPath, ILogger logger, bool nocache, bool extractPdbs, TrapWriter.CompressionMode trapCompression, out string trapFile, out bool extracted)
-        {
-            trapFile = "";
-            extracted = false;
-            try
-            {
-                var canonicalPathCache = CanonicalPathCache.Create(logger, 1000);
-                var pathTransformer = new PathTransformer(canonicalPathCache);
-                var extractor = new Extractor(false, assemblyPath, logger, pathTransformer);
-                var transformedAssemblyPath = pathTransformer.Transform(assemblyPath);
-                var project = layout.LookupProjectOrDefault(transformedAssemblyPath);
-                using var trapWriter = project.CreateTrapWriter(logger, transformedAssemblyPath.WithSuffix(".cil"), trapCompression, discardDuplicates: true);
-                trapFile = trapWriter.TrapFile;
-                if (nocache || !System.IO.File.Exists(trapFile))
-                {
-                    ExtractCIL(extractor, trapWriter, extractPdbs);
-                    extracted = true;
-                }
-            }
-            catch (Exception ex)  // lgtm[cs/catch-of-all-exceptions]
-            {
-                logger.Log(Severity.Error, string.Format("Exception extracting {0}: {1}", assemblyPath, ex));
-            }
-        }
     }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractedEntity.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractedEntity.cs
index 080227a63b9..d94b94df8a8 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractedEntity.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractedEntity.cs
@@ -5,7 +5,7 @@ namespace Semmle.Extraction.CIL
     /// <summary>
     /// A CIL entity which has been extracted.
     /// </summary>
-    public interface IExtractedEntity : IExtractionProduct, IEntity
+    internal interface IExtractedEntity : IExtractionProduct, IEntity
     {
         /// <summary>
         /// The contents of the entity.
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractionProduct.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractionProduct.cs
index 6383d7e1b4c..231a311a78c 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractionProduct.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IExtractionProduct.cs
@@ -12,7 +12,7 @@ namespace Semmle.Extraction.CIL
     /// - Enumerate Contents to produce more extraction products
     /// - Extract these until there is nothing left to extract
     /// </remarks>
-    public interface IExtractionProduct
+    internal interface IExtractionProduct
     {
         /// <summary>
         /// Perform further extraction/population of this item as necessary.
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IGenericContext.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IGenericContext.cs
index 21c69f7aeb4..65171e63cd0 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IGenericContext.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/IGenericContext.cs
@@ -6,7 +6,7 @@ namespace Semmle.Extraction.CIL
     /// When we decode a type/method signature, we need access to
     /// generic parameters.
     /// </summary>
-    public interface IGenericContext
+    internal interface IGenericContext
     {
         Context Cx { get; }
 
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/LabelledEntity.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/LabelledEntity.cs
index 80ef03a1821..26f6c00cd0b 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/LabelledEntity.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/LabelledEntity.cs
@@ -8,7 +8,7 @@ namespace Semmle.Extraction.CIL
     /// An entity that needs to be populated during extraction.
     /// This assigns a key and optionally extracts its contents.
     /// </summary>
-    public abstract class LabelledEntity : Extraction.LabelledEntity, IExtractedEntity
+    internal abstract class LabelledEntity : Extraction.LabelledEntity, IExtractedEntity
     {
         // todo: with .NET 5 this can override the base context, and change the return type.
         public Context Cx => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/UnlabelledEntity.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/UnlabelledEntity.cs
index 3c9924cc98f..42d3824c00c 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/UnlabelledEntity.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Base/UnlabelledEntity.cs
@@ -7,7 +7,7 @@ namespace Semmle.Extraction.CIL
     /// An entity that has contents to extract. There is no need to populate
     /// a key as it's done in the contructor.
     /// </summary>
-    public abstract class UnlabelledEntity : Extraction.UnlabelledEntity, IExtractedEntity
+    internal abstract class UnlabelledEntity : Extraction.UnlabelledEntity, IExtractedEntity
     {
         // todo: with .NET 5 this can override the base context, and change the return type.
         public Context Cx => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/ConstructedType.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/ConstructedType.cs
index be2ab5da4d8..6e2fb90beae 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/ConstructedType.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/ConstructedType.cs
@@ -9,7 +9,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// A constructed type.
     /// </summary>
-    public sealed class ConstructedType : Type
+    internal sealed class ConstructedType : Type
     {
         private readonly Type unboundGenericType;
 
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/File.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/File.cs
index ba447aebc3a..8e440795092 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/File.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/File.cs
@@ -3,7 +3,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CIL.Entities
 {
-    public class File : LabelledEntity, IFileOrFolder
+    internal class File : LabelledEntity, IFileOrFolder
     {
         protected string OriginalPath { get; }
         protected PathTransformer.ITransformedPath TransformedPath { get; }
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Folder.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Folder.cs
index 2294a525e4b..a502a005724 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Folder.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Folder.cs
@@ -3,7 +3,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CIL.Entities
 {
-    public sealed class Folder : LabelledEntity, IFileOrFolder
+    internal sealed class Folder : LabelledEntity, IFileOrFolder
     {
         private readonly PathTransformer.ITransformedPath transformedPath;
 
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Namespace.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Namespace.cs
index 5d498c5ac54..6cabce18795 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Namespace.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Namespace.cs
@@ -7,7 +7,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// A namespace.
     /// </summary>
-    public sealed class Namespace : TypeContainer
+    internal sealed class Namespace : TypeContainer
     {
         public Namespace? ParentNamespace { get; }
         public string Name { get; }
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/PdbSourceFile.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/PdbSourceFile.cs
index 5dd5dfa37e6..97e9948f6a7 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/PdbSourceFile.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/PdbSourceFile.cs
@@ -2,7 +2,7 @@ using System.Collections.Generic;
 
 namespace Semmle.Extraction.CIL.Entities
 {
-    public class PdbSourceFile : File
+    internal class PdbSourceFile : File
     {
         private readonly PDB.ISourceFile file;
 
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/PrimitiveType.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/PrimitiveType.cs
index 661ae0f535b..d807c5778de 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/PrimitiveType.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/PrimitiveType.cs
@@ -5,7 +5,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CIL.Entities
 {
-    public sealed class PrimitiveType : Type
+    internal sealed class PrimitiveType : Type
     {
         private readonly PrimitiveTypeCode typeCode;
         public PrimitiveType(Context cx, PrimitiveTypeCode tc) : base(cx)
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/SourceLocation.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/SourceLocation.cs
index 318cac14930..ff67844121a 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/SourceLocation.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/SourceLocation.cs
@@ -4,7 +4,7 @@ using Semmle.Extraction.PDB;
 
 namespace Semmle.Extraction.CIL.Entities
 {
-    public sealed class PdbSourceLocation : LabelledEntity, ILocation
+    internal sealed class PdbSourceLocation : LabelledEntity, ILocation
     {
         private readonly Location location;
         private readonly PdbSourceFile file;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/Type.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/Type.cs
index ad5a6ababaa..9b452777031 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/Type.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/Type.cs
@@ -9,7 +9,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// A type.
     /// </summary>
-    public abstract class Type : TypeContainer, IMember
+    internal abstract class Type : TypeContainer, IMember
     {
         internal const string AssemblyTypeNameSeparator = "::";
         internal const string PrimitiveTypePrefix = "builtin" + AssemblyTypeNameSeparator + "System.";
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeContainer.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeContainer.cs
index 106b6fe83be..e201e065255 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeContainer.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeContainer.cs
@@ -6,7 +6,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// Base class for all type containers (namespaces, types, methods).
     /// </summary>
-    public abstract class TypeContainer : LabelledEntity, IGenericContext
+    internal abstract class TypeContainer : LabelledEntity, IGenericContext
     {
         protected TypeContainer(Context cx) : base(cx)
         {
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeDefinitionType.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeDefinitionType.cs
index 461141ae719..3f9df14a891 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeDefinitionType.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeDefinitionType.cs
@@ -11,7 +11,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// A type defined in the current assembly.
     /// </summary>
-    public sealed class TypeDefinitionType : Type
+    internal sealed class TypeDefinitionType : Type
     {
         private readonly TypeDefinitionHandle handle;
         private readonly TypeDefinition td;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeReferenceType.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeReferenceType.cs
index 49a15965dd0..51677bf0bb9 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeReferenceType.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeReferenceType.cs
@@ -9,7 +9,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// A type reference, to a type in a referenced assembly.
     /// </summary>
-    public sealed class TypeReferenceType : Type
+    internal sealed class TypeReferenceType : Type
     {
         private readonly TypeReferenceHandle handle;
         private readonly TypeReference tr;
diff --git a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeSignatureDecoder.cs b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeSignatureDecoder.cs
index 4417becc58d..d1022d58f0c 100644
--- a/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeSignatureDecoder.cs
+++ b/csharp/extractor/Semmle.Extraction.CIL/Entities/TypeSignatureDecoder.cs
@@ -8,7 +8,7 @@ namespace Semmle.Extraction.CIL.Entities
     /// <summary>
     /// Decodes a type signature and produces a Type, for use by DecodeSignature() and friends.
     /// </summary>
-    public class TypeSignatureDecoder : ISignatureTypeProvider<Type, IGenericContext>
+    internal class TypeSignatureDecoder : ISignatureTypeProvider<Type, IGenericContext>
     {
         private readonly Context cx;
 
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Analyser.cs b/csharp/extractor/Semmle.Extraction.CSharp/Analyser.cs
index cf4f4e0ebf0..5ef8bd24d4e 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Analyser.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Analyser.cs
@@ -310,7 +310,7 @@ namespace Semmle.Extraction.CSharp
         {
             var stopwatch = new Stopwatch();
             stopwatch.Start();
-            CIL.Entities.Assembly.ExtractCIL(layout, r.FilePath, Logger, !options.Cache, options.PDB, options.TrapCompression, out var trapFile, out var extracted);
+            CIL.Analyser.ExtractCIL(layout, r.FilePath, Logger, !options.Cache, options.PDB, options.TrapCompression, out var trapFile, out var extracted);
             stopwatch.Stop();
             ReportProgress(r.FilePath, trapFile, stopwatch.Elapsed, extracted ? AnalysisAction.Extracted : AnalysisAction.UpToDate);
         }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/CachedEntityFactory.cs b/csharp/extractor/Semmle.Extraction.CSharp/CachedEntityFactory.cs
index 648d90be67f..2673ed0d7ef 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/CachedEntityFactory.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/CachedEntityFactory.cs
@@ -1,11 +1,9 @@
-using Microsoft.CodeAnalysis;
-
 namespace Semmle.Extraction.CSharp
 {
     /// <summary>
     /// A factory for creating cached entities.
     /// </summary>
-    public abstract class CachedEntityFactory<TInit, TEntity>
+    internal abstract class CachedEntityFactory<TInit, TEntity>
         : Extraction.CachedEntityFactory<TInit, TEntity> where TEntity : CachedEntity
     {
         /// <summary>
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Context.cs b/csharp/extractor/Semmle.Extraction.CSharp/Context.cs
index 181795fbe91..314706c1e47 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Context.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Context.cs
@@ -2,6 +2,7 @@ using Microsoft.CodeAnalysis;
 using System;
 using System.Diagnostics.CodeAnalysis;
 using Semmle.Extraction.Entities;
+using System.Collections.Generic;
 
 namespace Semmle.Extraction.CSharp
 {
@@ -9,7 +10,7 @@ namespace Semmle.Extraction.CSharp
     /// State that needs to be available throughout the extraction process.
     /// There is one Context object per trap output file.
     /// </summary>
-    public class Context : Extraction.Context
+    internal class Context : Extraction.Context
     {
         /// <summary>
         /// The program database provided by Roslyn.
@@ -50,7 +51,7 @@ namespace Semmle.Extraction.CSharp
 
         public bool IsAssemblyScope => scope is AssemblyScope;
 
-        public SyntaxTree SourceTree => scope is SourceScope sc ? sc.SourceTree : null;
+        private SyntaxTree SourceTree => scope is SourceScope sc ? sc.SourceTree : null;
 
         /// <summary>
         ///     Whether the given symbol needs to be defined in this context.
@@ -116,5 +117,28 @@ namespace Semmle.Extraction.CSharp
             loc = null;
             return false;
         }
+
+        private readonly HashSet<Label> extractedGenerics = new HashSet<Label>();
+
+        /// <summary>
+        /// Should the given entity be extracted?
+        /// A second call to this method will always return false,
+        /// on the assumption that it would have been extracted on the first call.
+        ///
+        /// This is used to track the extraction of generics, which cannot be extracted
+        /// in a top-down manner.
+        /// </summary>
+        /// <param name="entity">The entity to extract.</param>
+        /// <returns>True only on the first call for a particular entity.</returns>
+        internal bool ExtractGenerics(CachedEntity entity)
+        {
+            if (extractedGenerics.Contains(entity.Label))
+            {
+                return false;
+            }
+
+            extractedGenerics.Add(entity.Label);
+            return true;
+        }
     }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Assembly.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Assembly.cs
index 57ae72420d3..14209b39853 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Assembly.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Assembly.cs
@@ -4,7 +4,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class Assembly : Extraction.Entities.Location
+    internal class Assembly : Extraction.Entities.Location
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         private new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedEntity.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedEntity.cs
index 3296880f698..0376d8ab743 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedEntity.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedEntity.cs
@@ -1,6 +1,6 @@
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public abstract class CachedEntity<T> : Extraction.CachedEntity<T>
+    internal abstract class CachedEntity<T> : Extraction.CachedEntity<T>
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         protected new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedSymbol.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedSymbol.cs
index 3be67e7587f..28128a1871c 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedSymbol.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/CachedSymbol.cs
@@ -9,7 +9,7 @@ using System.Reflection.Metadata.Ecma335;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public abstract class CachedSymbol<T> : CachedEntity<T> where T : ISymbol
+    internal abstract class CachedSymbol<T> : CachedEntity<T> where T : ISymbol
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         protected new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
index f9c7357fe28..52ac3429a04 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
@@ -6,7 +6,7 @@ using Semmle.Util;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class Compilation : CachedEntity<object>
+    internal class Compilation : CachedEntity<object>
     {
         private static (string Cwd, string[] Args) settings;
         private static int hashCode;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Constructor.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Constructor.cs
index fc24bf2be61..f48a1f546ad 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Constructor.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Constructor.cs
@@ -8,7 +8,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class Constructor : Method
+    internal class Constructor : Method
     {
         private Constructor(Context cx, IMethodSymbol init)
             : base(cx, init) { }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Binary.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Binary.cs
index 74dcc9ff85f..5153c856a25 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Binary.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Binary.cs
@@ -23,12 +23,13 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
 
         private static ExprKind GetKind(Context cx, BinaryExpressionSyntax node)
         {
-            var k = GetBinaryTokenKind(cx, node.OperatorToken.Kind());
+            var k = GetBinaryTokenKind(cx, node);
             return GetCallType(cx, node).AdjustKind(k);
         }
 
-        private static ExprKind GetBinaryTokenKind(Context cx, SyntaxKind kind)
+        private static ExprKind GetBinaryTokenKind(Context cx, BinaryExpressionSyntax node)
         {
+            var kind = node.OperatorToken.Kind();
             switch (kind)
             {
                 case SyntaxKind.LessThanToken: return ExprKind.LT;
@@ -54,7 +55,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 case SyntaxKind.QuestionQuestionToken: return ExprKind.NULL_COALESCING;
                 // !! And the rest
                 default:
-                    cx.ModelError($"Unhandled operator type {kind}");
+                    cx.ModelError(node, $"Unhandled operator type {kind}");
                     return ExprKind.UNKNOWN;
             }
         }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/BaseObjectCreation.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/BaseObjectCreation.cs
index 6f2c38b63db..286ddae254b 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/BaseObjectCreation.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/BaseObjectCreation.cs
@@ -52,7 +52,7 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                         ObjectInitializer.Create(new ExpressionNodeInfo(Context, Syntax.Initializer, this, -1).SetType(Type));
                         break;
                     default:
-                        Context.ModelError("Unhandled initializer in object creation");
+                        Context.ModelError(Syntax.Initializer, "Unhandled initializer in object creation");
                         break;
                 }
             }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/File.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/File.cs
index 6c0c33ff392..6386759f590 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/File.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/File.cs
@@ -6,7 +6,7 @@ using System.Linq;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class File : Extraction.Entities.File
+    internal class File : Extraction.Entities.File
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         private new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/FreshEntity.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/FreshEntity.cs
index 3776dc9552a..b77d5766fe0 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/FreshEntity.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/FreshEntity.cs
@@ -1,6 +1,6 @@
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public abstract class FreshEntity : Extraction.FreshEntity
+    internal abstract class FreshEntity : Extraction.FreshEntity
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         protected new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs
index 8a1572796bc..4f90d4e577c 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs
@@ -8,7 +8,7 @@ using System.Linq;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public abstract class Method : CachedSymbol<IMethodSymbol>, IExpressionParentEntity, IStatementParentEntity
+    internal abstract class Method : CachedSymbol<IMethodSymbol>, IExpressionParentEntity, IStatementParentEntity
     {
         protected Method(Context cx, IMethodSymbol init)
             : base(cx, init) { }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/NonGeneratedSourceLocation.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/NonGeneratedSourceLocation.cs
index ee62be6f405..279c52cdbcc 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/NonGeneratedSourceLocation.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/NonGeneratedSourceLocation.cs
@@ -3,7 +3,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class NonGeneratedSourceLocation : Extraction.Entities.SourceLocation
+    internal class NonGeneratedSourceLocation : Extraction.Entities.SourceLocation
     {
         // todo: this can be changed to an override after the .NET 5 upgrade
         private new Context Context => (Context)base.Context;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Parameter.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Parameter.cs
index 7ca9ce06c37..ca4459c728a 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Parameter.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Parameter.cs
@@ -7,7 +7,7 @@ using System.IO;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public class Parameter : CachedSymbol<IParameterSymbol>, IExpressionParentEntity
+    internal class Parameter : CachedSymbol<IParameterSymbol>, IExpressionParentEntity
     {
         protected IEntity Parent { get; set; }
         protected Parameter Original { get; }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Nullability.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Nullability.cs
index 37278a7cf88..5c5aa465b0b 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Nullability.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Nullability.cs
@@ -5,7 +5,7 @@ using System.Linq;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public sealed class Nullability
+    internal sealed class Nullability
     {
         public int Annotation { get; }
 
@@ -96,7 +96,7 @@ namespace Semmle.Extraction.CSharp.Entities
         }
     }
 
-    public class NullabilityEntity : CachedEntity<Nullability>
+    internal class NullabilityEntity : CachedEntity<Nullability>
     {
         public NullabilityEntity(Context cx, Nullability init) : base(cx, init)
         {
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
index 22a5f9e1284..ed823cac058 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
@@ -8,7 +8,7 @@ using System.Linq;
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    public abstract class Type : CachedSymbol<ITypeSymbol>
+    internal abstract class Type : CachedSymbol<ITypeSymbol>
     {
         protected Type(Context cx, ITypeSymbol init)
             : base(cx, init) { }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/UserOperator.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/UserOperator.cs
index e4ca6810017..1c19b1c74cb 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/UserOperator.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/UserOperator.cs
@@ -18,7 +18,7 @@ namespace Semmle.Extraction.CSharp.Entities
             var returnType = Type.Create(Context, Symbol.ReturnType);
             trapFile.operators(this,
                 Symbol.Name,
-                OperatorSymbol(Context, Symbol.Name),
+                OperatorSymbol(Context, Symbol),
                 ContainingType,
                 returnType.TypeRef,
                 (UserOperator)OriginalDefinition);
@@ -176,10 +176,11 @@ namespace Semmle.Extraction.CSharp.Entities
         /// <param name="cx">Extractor context.</param>
         /// <param name="methodName">The method name.</param>
         /// <returns>The converted name.</returns>
-        public static string OperatorSymbol(Context cx, string methodName)
+        private static string OperatorSymbol(Context cx, IMethodSymbol method)
         {
+            var methodName = method.Name;
             if (!OperatorSymbol(methodName, out var result))
-                cx.ModelError($"Unhandled operator name in OperatorSymbol(): '{methodName}'");
+                cx.ModelError(method, $"Unhandled operator name in OperatorSymbol(): '{methodName}'");
             return result;
         }
 
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Populators/TypeContainerVisitor.cs b/csharp/extractor/Semmle.Extraction.CSharp/Populators/TypeContainerVisitor.cs
index 8dafeb393d6..6d2226048e3 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Populators/TypeContainerVisitor.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Populators/TypeContainerVisitor.cs
@@ -9,7 +9,7 @@ using System.Linq;
 
 namespace Semmle.Extraction.CSharp.Populators
 {
-    public class TypeContainerVisitor : CSharpSyntaxVisitor
+    internal class TypeContainerVisitor : CSharpSyntaxVisitor
     {
         protected Context Cx { get; }
         protected IEntity Parent { get; }
diff --git a/csharp/extractor/Semmle.Extraction/Context.cs b/csharp/extractor/Semmle.Extraction/Context.cs
index f30ecdfcdfa..20f92916f46 100644
--- a/csharp/extractor/Semmle.Extraction/Context.cs
+++ b/csharp/extractor/Semmle.Extraction/Context.cs
@@ -35,19 +35,19 @@ namespace Semmle.Extraction
         // A recursion guard against writing to the trap file whilst writing an id to the trap file.
         private bool writingLabel = false;
 
-        public void DefineLabel(IEntity entity, TextWriter trapFile, Extractor extractor)
+        protected void DefineLabel(IEntity entity)
         {
             if (writingLabel)
             {
                 // Don't define a label whilst writing a label.
-                PopulateLater(() => DefineLabel(entity, trapFile, extractor));
+                PopulateLater(() => DefineLabel(entity));
             }
             else
             {
                 try
                 {
                     writingLabel = true;
-                    entity.DefineLabel(trapFile, extractor);
+                    entity.DefineLabel(TrapWriter.Writer, Extractor);
                 }
                 finally
                 {
@@ -70,13 +70,13 @@ namespace Semmle.Extraction
         }
 #endif
 
-        public Label GetNewLabel() => new Label(GetNewId());
+        protected Label GetNewLabel() => new Label(GetNewId());
 
-        public TEntity CreateEntity<TInit, TEntity>(CachedEntityFactory<TInit, TEntity> factory, object cacheKey, TInit init)
+        internal TEntity CreateEntity<TInit, TEntity>(CachedEntityFactory<TInit, TEntity> factory, object cacheKey, TInit init)
             where TEntity : CachedEntity =>
                 cacheKey is ISymbol s ? CreateEntity(factory, s, init, symbolEntityCache) : CreateEntity(factory, cacheKey, init, objectEntityCache);
 
-        public TEntity CreateEntityFromSymbol<TSymbol, TEntity>(CachedEntityFactory<TSymbol, TEntity> factory, TSymbol init)
+        internal TEntity CreateEntityFromSymbol<TSymbol, TEntity>(CachedEntityFactory<TSymbol, TEntity> factory, TSymbol init)
             where TSymbol : ISymbol
             where TEntity : CachedEntity => CreateEntity(factory, init, init, symbolEntityCache);
 
@@ -103,7 +103,7 @@ namespace Semmle.Extraction
 
                 dictionary[cacheKey] = entity;
 
-                DefineLabel(entity, TrapWriter.Writer, Extractor);
+                DefineLabel(entity);
                 if (entity.NeedsPopulation)
                     Populate(init as ISymbol, entity);
 
@@ -117,32 +117,11 @@ namespace Semmle.Extraction
             }
         }
 
-        /// <summary>
-        /// Should the given entity be extracted?
-        /// A second call to this method will always return false,
-        /// on the assumption that it would have been extracted on the first call.
-        ///
-        /// This is used to track the extraction of generics, which cannot be extracted
-        /// in a top-down manner.
-        /// </summary>
-        /// <param name="entity">The entity to extract.</param>
-        /// <returns>True only on the first call for a particular entity.</returns>
-        public bool ExtractGenerics(CachedEntity entity)
-        {
-            if (extractedGenerics.Contains(entity.Label))
-            {
-                return false;
-            }
-
-            extractedGenerics.Add(entity.Label);
-            return true;
-        }
-
         /// <summary>
         /// Creates a fresh label with ID "*", and set it on the
         /// supplied <paramref name="entity"/> object.
         /// </summary>
-        public void AddFreshLabel(Entity entity)
+        internal void AddFreshLabel(Entity entity)
         {
             entity.Label = GetNewLabel();
             entity.DefineFreshLabel(TrapWriter.Writer);
@@ -154,7 +133,6 @@ namespace Semmle.Extraction
 
         private readonly IDictionary<object, CachedEntity> objectEntityCache = new Dictionary<object, CachedEntity>();
         private readonly IDictionary<ISymbol, CachedEntity> symbolEntityCache = new Dictionary<ISymbol, CachedEntity>(10000, SymbolEqualityComparer.Default);
-        private readonly HashSet<Label> extractedGenerics = new HashSet<Label>();
 
         /// <summary>
         /// Queue of items to populate later.
@@ -204,11 +182,11 @@ namespace Semmle.Extraction
             }
         }
 
-        public Context(Extractor e, TrapWriter trapWriter, bool addAssemblyTrapPrefix = false)
+        protected Context(Extractor extractor, TrapWriter trapWriter, bool shouldAddAssemblyTrapPrefix = false)
         {
-            Extractor = e;
+            Extractor = extractor;
             TrapWriter = trapWriter;
-            ShouldAddAssemblyTrapPrefix = addAssemblyTrapPrefix;
+            ShouldAddAssemblyTrapPrefix = shouldAddAssemblyTrapPrefix;
         }
 
         private int currentRecursiveDepth = 0;
@@ -277,7 +255,7 @@ namespace Semmle.Extraction
         /// <param name="optionalSymbol">Symbol for reporting errors.</param>
         /// <param name="entity">The entity to populate.</param>
         /// <exception cref="InternalError">Thrown on invalid trap stack behaviour.</exception>
-        public void Populate(ISymbol? optionalSymbol, CachedEntity entity)
+        private void Populate(ISymbol? optionalSymbol, CachedEntity entity)
         {
             if (writingLabel)
             {
@@ -372,7 +350,7 @@ namespace Semmle.Extraction
         /// <param name="message">The text of the message.</param>
         /// <param name="optionalSymbol">The symbol of the error, or null.</param>
         /// <param name="optionalEntity">The entity of the error, or null.</param>
-        public void ExtractionError(string message, ISymbol? optionalSymbol, Entity optionalEntity)
+        private void ExtractionError(string message, ISymbol? optionalSymbol, Entity optionalEntity)
         {
             if (!(optionalSymbol is null))
             {
@@ -392,9 +370,9 @@ namespace Semmle.Extraction
         /// Log an extraction message.
         /// </summary>
         /// <param name="msg">The message to log.</param>
-        public void ExtractionError(Message msg)
+        private void ExtractionError(Message msg)
         {
-            new Entities.ExtractionMessage(this, msg);
+            new ExtractionMessage(this, msg);
             Extractor.Message(msg);
         }
 
@@ -412,7 +390,7 @@ namespace Semmle.Extraction
         /// <summary>
         /// Signal an error in the program model.
         /// </summary>
-        /// <param name="node">Symbol causing the error.</param>
+        /// <param name="symbol">Symbol causing the error.</param>
         /// <param name="msg">The error message.</param>
         public void ModelError(ISymbol symbol, string msg)
         {