diff --git a/csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpDiagnosticClassifier.cs b/csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpDiagnosticClassifier.cs
index 85d6c872c84b4..2f947d7c33d42 100644
--- a/csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpDiagnosticClassifier.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpDiagnosticClassifier.cs
@@ -99,7 +99,7 @@ public override void Fire(DiagnosticClassifier classifier, Match match)
         {
             if (!match.Groups.TryGetValue("projectFile", out var projectFile))
                 throw new ArgumentException("Expected regular expression match to contain projectFile");
-            if (!match.Groups.TryGetValue("location", out var location))
+            if (!match.Groups.TryGetValue("location", out _))
                 throw new ArgumentException("Expected regular expression match to contain location");
 
             var result = classifier.Results.OfType<Result>().FirstOrDefault();
diff --git a/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs b/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
index 20ed6f0e4129e..43efcd0352f0d 100644
--- a/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
@@ -1,9 +1,7 @@
 using System;
 using System.Collections.Generic;
-using System.IO;
 using System.Linq;
 using Semmle.Util;
-using Semmle.Util.Logging;
 using Semmle.Autobuild.Shared;
 using Semmle.Extraction.CSharp.DependencyFetching;
 
@@ -15,14 +13,14 @@ namespace Semmle.Autobuild.CSharp
     /// </summary>
     internal class DotNetRule : IBuildRule<CSharpAutobuildOptions>
     {
-        public readonly List<IProjectOrSolution> FailedProjectsOrSolutions = new();
+        public List<IProjectOrSolution> FailedProjectsOrSolutions { get; } = [];
 
         /// <summary>
         /// A list of projects which are incompatible with DotNet.
         /// </summary>
         public IEnumerable<Project<CSharpAutobuildOptions>> NotDotNetProjects { get; private set; }
 
-        public DotNetRule() => NotDotNetProjects = new List<Project<CSharpAutobuildOptions>>();
+        public DotNetRule() => NotDotNetProjects = [];
 
         public BuildScript Analyse(IAutobuilder<CSharpAutobuildOptions> builder, bool auto)
         {
diff --git a/csharp/autobuilder/Semmle.Autobuild.Shared/BuildTools.cs b/csharp/autobuilder/Semmle.Autobuild.Shared/BuildTools.cs
index 0e910b68d48ab..c445fcb805a0c 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Shared/BuildTools.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Shared/BuildTools.cs
@@ -18,7 +18,7 @@ public VcVarsBatFile(string path, int version)
             Path = path;
             ToolsVersion = version;
         }
-    };
+    }
 
     /// <summary>
     /// Collection of available Visual Studio build tools.
diff --git a/csharp/autobuilder/Semmle.Autobuild.Shared/DiagnosticClassifier.cs b/csharp/autobuilder/Semmle.Autobuild.Shared/DiagnosticClassifier.cs
index 94af39ca9598d..43db196d9f692 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Shared/DiagnosticClassifier.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Shared/DiagnosticClassifier.cs
@@ -60,7 +60,7 @@ public virtual void Fire(DiagnosticClassifier classifier, Match match) { }
     public class DiagnosticClassifier
     {
         private readonly List<DiagnosticRule> rules;
-        public readonly List<IDiagnosticsResult> Results;
+        public List<IDiagnosticsResult> Results { get; }
 
         public DiagnosticClassifier()
         {
diff --git a/csharp/autobuilder/Semmle.Autobuild.Shared/MsBuildRule.cs b/csharp/autobuilder/Semmle.Autobuild.Shared/MsBuildRule.cs
index eaf9449af417b..139e16566e835 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Shared/MsBuildRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Shared/MsBuildRule.cs
@@ -32,7 +32,7 @@ public class MsBuildRule : IBuildRule<AutobuildOptionsShared>
         /// <summary>
         /// A list of solutions or projects which failed to build.
         /// </summary>
-        public readonly List<IProjectOrSolution> FailedProjectsOrSolutions = new();
+        public List<IProjectOrSolution> FailedProjectsOrSolutions { get; } = [];
 
         public BuildScript Analyse(IAutobuilder<AutobuildOptionsShared> builder, bool auto)
         {
@@ -60,7 +60,7 @@ public BuildScript Analyse(IAutobuilder<AutobuildOptionsShared> builder, bool au
             // Use `nuget.exe` from source code repo, if present, otherwise first attempt with global
             // `nuget` command, and if that fails, attempt to download `nuget.exe` from nuget.org
             var nuget = builder.GetFilename("nuget.exe").Select(t => t.Item1).FirstOrDefault() ?? "nuget";
-            var nugetDownloadPath = builder.Actions.PathCombine(FileUtils.GetTemporaryWorkingDirectory(builder.Actions.GetEnvironmentVariable, builder.Options.Language.UpperCaseName, out var _), ".nuget", "nuget.exe");
+            var nugetDownloadPath = builder.Actions.PathCombine(FileUtils.GetTemporaryWorkingDirectory(builder.Actions.GetEnvironmentVariable, builder.Options.Language.UpperCaseName, out _), ".nuget", "nuget.exe");
             var nugetDownloaded = false;
 
             var ret = BuildScript.Success;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyCache.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyCache.cs
index 62a053870e914..953c0adc55215 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyCache.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyCache.cs
@@ -133,12 +133,12 @@ public AssemblyInfo GetAssemblyInfo(string filepath)
 
         private readonly List<string> dllsToIndex = new List<string>();
 
-        private readonly Dictionary<string, AssemblyInfo> assemblyInfoByFileName = new Dictionary<string, AssemblyInfo>();
+        private readonly Dictionary<string, AssemblyInfo> assemblyInfoByFileName = [];
 
         // Map from assembly id (in various formats) to the full info.
-        private readonly Dictionary<string, AssemblyInfo> assemblyInfoById = new Dictionary<string, AssemblyInfo>();
+        private readonly Dictionary<string, AssemblyInfo> assemblyInfoById = [];
 
-        private readonly HashSet<string> failedAssemblyInfoIds = new HashSet<string>();
+        private readonly HashSet<string> failedAssemblyInfoIds = [];
 
         private readonly ILogger logger;
     }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyInfo.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyInfo.cs
index d77005bf458bf..b02f33842a609 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyInfo.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/AssemblyInfo.cs
@@ -94,7 +94,7 @@ private AssemblyInfo(string id, string filename)
         {
             var sections = id.Split(new string[] { ", " }, StringSplitOptions.None);
 
-            Name = sections.First();
+            Name = sections[0];
 
             foreach (var section in sections.Skip(1))
             {
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/Assets.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/Assets.cs
index 9308a137e7e36..ef2c47397b05e 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/Assets.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/Assets.cs
@@ -120,8 +120,6 @@ private void AddPackageDependencies(JObject json, string jsonPath)
                     info.Compile
                         .ForEach(r => Dependencies.Add(name, r.Key));
                 });
-
-            return;
         }
 
         /// <summary>
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyContainer.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyContainer.cs
index 2307311041246..b5abefb3a651d 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyContainer.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyContainer.cs
@@ -12,12 +12,12 @@ internal class DependencyContainer
         /// <summary>
         /// Paths to dependencies required for compilation.
         /// </summary>
-        public HashSet<string> Paths { get; } = new();
+        public HashSet<string> Paths { get; } = [];
 
         /// <summary>
         /// Packages that are used as a part of the required dependencies.
         /// </summary>
-        public HashSet<string> Packages { get; } = new();
+        public HashSet<string> Packages { get; } = [];
 
         /// <summary>
         /// If the path specifically adds a .dll we use that, otherwise we as a fallback
@@ -33,9 +33,7 @@ private static string ParseFilePath(string path)
         }
 
         private static string GetPackageName(string package) =>
-            package
-                .Split(Path.DirectorySeparatorChar)
-                .First();
+            package.Split(Path.DirectorySeparatorChar)[0];
 
         /// <summary>
         /// Add a dependency inside a package.
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
index f18d30f4f1925..4866df1260e2a 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
@@ -310,7 +310,7 @@ private void AddNetFrameworkDlls(ISet<AssemblyLookupLocation> dllLocations, ISet
 
             if (runtimeLocation is null)
             {
-                runtimeLocation ??= Runtime.ExecutingRuntime;
+                runtimeLocation = Runtime.ExecutingRuntime;
                 dllLocations.Add(new AssemblyLookupLocation(runtimeLocation, name => !name.StartsWith("Semmle.")));
             }
             else
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNetCliInvoker.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNetCliInvoker.cs
index 1267802122706..4295cce671679 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNetCliInvoker.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNetCliInvoker.cs
@@ -58,13 +58,13 @@ private bool RunCommandAux(string args, string? workingDirectory, out IList<stri
             return true;
         }
 
-        public bool RunCommand(string args, bool silent) =>
+        public bool RunCommand(string args, bool silent = true) =>
             RunCommandAux(args, null, out _, silent);
 
-        public bool RunCommand(string args, out IList<string> output, bool silent) =>
+        public bool RunCommand(string args, out IList<string> output, bool silent = true) =>
             RunCommandAux(args, null, out output, silent);
 
-        public bool RunCommand(string args, string? workingDirectory, out IList<string> output, bool silent) =>
+        public bool RunCommand(string args, string? workingDirectory, out IList<string> output, bool silent = true) =>
             RunCommandAux(args, workingDirectory, out output, silent);
     }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/EnvironmentVariableNames.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/EnvironmentVariableNames.cs
index d9a0eac4845af..345cb43453fc7 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/EnvironmentVariableNames.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/EnvironmentVariableNames.cs
@@ -1,6 +1,6 @@
 namespace Semmle.Extraction.CSharp.DependencyFetching
 {
-    internal class EnvironmentVariableNames
+    internal static class EnvironmentVariableNames
     {
         /// <summary>
         /// Controls whether to generate source files from resources (`.resx`).
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetExeWrapper.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetExeWrapper.cs
index 262ae4b19edd0..0371aed16e2df 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetExeWrapper.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetExeWrapper.cs
@@ -51,7 +51,7 @@ public NugetExeWrapper(FileProvider fileProvider, TemporaryDirectory packageDire
                     {
                         if (File.Exists(nugetConfigPath))
                         {
-                            var tempFolderPath = FileUtils.GetTemporaryWorkingDirectory(out var _);
+                            var tempFolderPath = FileUtils.GetTemporaryWorkingDirectory(out _);
 
                             do
                             {
@@ -188,7 +188,7 @@ private bool TryRestoreNugetPackage(string packagesConfig)
             var threadId = Environment.CurrentManagedThreadId;
             void onOut(string s) => logger.LogDebug(s, threadId);
             void onError(string s) => logger.LogError(s, threadId);
-            var exitCode = pi.ReadOutput(out var _, onOut, onError);
+            var exitCode = pi.ReadOutput(out _, onOut, onError);
             if (exitCode != 0)
             {
                 logger.LogError($"Command {pi.FileName} {pi.Arguments} failed with exit code {exitCode}");
@@ -264,7 +264,7 @@ private void RunMonoNugetCommand(string command, out IList<string> stdout)
         private void AddDefaultPackageSource(string nugetConfig)
         {
             logger.LogInfo("Adding default package source...");
-            RunMonoNugetCommand($"sources add -Name DefaultNugetOrg -Source {NugetPackageRestorer.PublicNugetOrgFeed} -ConfigFile \"{nugetConfig}\"", out var _);
+            RunMonoNugetCommand($"sources add -Name DefaultNugetOrg -Source {NugetPackageRestorer.PublicNugetOrgFeed} -ConfigFile \"{nugetConfig}\"", out _);
         }
 
         public void Dispose()
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackageRestorer.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackageRestorer.cs
index 0204e9b7c408f..4ad4c8c9e31a1 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackageRestorer.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackageRestorer.cs
@@ -538,7 +538,7 @@ private void TryChangePackageVersion(DirectoryInfo tempDir, string newVersion)
             TryChangeProjectFile(tempDir, PackageReferenceVersion(), $"Version=\"{newVersion}\"", "package reference version");
         }
 
-        private bool TryChangeProjectFile(DirectoryInfo projectDir, Regex pattern, string replacement, string patternName)
+        private void TryChangeProjectFile(DirectoryInfo projectDir, Regex pattern, string replacement, string patternName)
         {
             try
             {
@@ -548,7 +548,7 @@ private bool TryChangeProjectFile(DirectoryInfo projectDir, Regex pattern, strin
                 if (csprojs.Length != 1)
                 {
                     logger.LogError($"Could not find the .csproj file in {projectDir.FullName}, count = {csprojs.Length}");
-                    return false;
+                    return;
                 }
 
                 var csproj = csprojs[0];
@@ -557,18 +557,16 @@ private bool TryChangeProjectFile(DirectoryInfo projectDir, Regex pattern, strin
                 if (matches.Count == 0)
                 {
                     logger.LogError($"Could not find the {patternName} in {csproj.FullName}");
-                    return false;
+                    return;
                 }
 
                 content = pattern.Replace(content, replacement, 1);
                 File.WriteAllText(csproj.FullName, content);
-                return true;
             }
             catch (Exception exc)
             {
                 logger.LogError($"Failed to change the {patternName} in {projectDir.FullName}: {exc}");
             }
-            return false;
         }
 
         private static async Task ExecuteGetRequest(string address, HttpClient httpClient, CancellationToken cancellationToken)
@@ -644,7 +642,7 @@ private bool CheckFeeds(out HashSet<string> explicitFeeds)
             (explicitFeeds, var allFeeds) = GetAllFeeds();
 
             var excludedFeeds = EnvironmentVariables.GetURLs(EnvironmentVariableNames.ExcludedNugetFeedsFromResponsivenessCheck)
-                .ToHashSet() ?? [];
+                .ToHashSet();
 
             if (excludedFeeds.Count > 0)
             {
@@ -779,7 +777,7 @@ private static string ComputeTempDirectoryPath(string srcDir, string subfolderNa
             foreach (var b in sha.Take(8))
                 sb.AppendFormat("{0:x2}", b);
 
-            return Path.Combine(FileUtils.GetTemporaryWorkingDirectory(out var _), sb.ToString(), subfolderName);
+            return Path.Combine(FileUtils.GetTemporaryWorkingDirectory(out _), sb.ToString(), subfolderName);
         }
     }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.StubGenerator/StubVisitor.cs b/csharp/extractor/Semmle.Extraction.CSharp.StubGenerator/StubVisitor.cs
index 56a20473fa3f2..80f6b2d6617b9 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.StubGenerator/StubVisitor.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.StubGenerator/StubVisitor.cs
@@ -201,12 +201,12 @@ private void StubTypedConstant(TypedConstant c)
         }
     }
 
-    private static readonly HashSet<string> attributeAllowList = new() {
+    private static readonly HashSet<string> attributeAllowList = [
         "System.FlagsAttribute",
         "System.AttributeUsageAttribute",
         "System.Runtime.CompilerServices.InterpolatedStringHandlerAttribute",
         "System.Runtime.CompilerServices.InterpolatedStringHandlerArgumentAttribute",
-    };
+    ];
 
     private void StubAttribute(AttributeData a, string prefix, bool addNewLine)
     {
@@ -298,7 +298,7 @@ private static bool IsUnsafe(ITypeSymbol symbol) =>
         (symbol is INamedTypeSymbol named && named.TypeArguments.Any(IsUnsafe)) ||
         (symbol is IArrayTypeSymbol at && IsUnsafe(at.ElementType));
 
-    private static readonly HashSet<string> keywords = new() {
+    private static readonly HashSet<string> keywords = [
         "abstract", "as", "base", "bool", "break", "byte", "case", "catch", "char", "checked",
         "class", "const", "continue", "decimal", "default", "delegate", "do", "double", "else",
         "enum", "event", "explicit", "extern", "false", "finally", "fixed", "float", "for", "foreach",
@@ -308,7 +308,7 @@ private static bool IsUnsafe(ITypeSymbol symbol) =>
         "stackalloc", "static", "string", "struct", "switch", "this", "throw", "true", "try",
         "typeof", "uint", "ulong", "unchecked", "unsafe", "ushort", "using", "virtual", "void",
         "volatile", "while"
-    };
+    ];
 
     private static string EscapeIdentifier(string identifier) =>
         keywords.Contains(identifier) ? "@" + identifier : identifier;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentBinding.cs b/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentBinding.cs
index 22518ba493016..2089cf7d8fe60 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentBinding.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentBinding.cs
@@ -9,5 +9,5 @@ public enum CommentBinding
         Best,       // The most likely element associated with a comment
         Before,     // The element before the comment
         After       // The element after the comment
-    };
+    }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentLineType.cs b/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentLineType.cs
index 8506ca701b3e0..94ef2dbfa4b82 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentLineType.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Comments/CommentLineType.cs
@@ -9,5 +9,5 @@ public enum CommentLineType
         XmlDoc,                 // Comment starting /// ...
         Multiline,              // Comment starting /* ..., even if the comment only spans one line.
         MultilineContinuation   // The second and subsequent lines of comment in a multiline comment.
-    };
+    }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
index 0ba1965723eb8..8685c9d7a7dc3 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Compilations/Compilation.cs
@@ -9,7 +9,7 @@ namespace Semmle.Extraction.CSharp.Entities
 {
     internal class Compilation : CachedEntity<object>
     {
-        internal readonly ConcurrentDictionary<string, int> messageCounts = new();
+        internal readonly ConcurrentDictionary<string, int> messageCounts = [];
 
         private readonly string cwd;
         private readonly string[] args;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/ExpressionNodeInfo.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/ExpressionNodeInfo.cs
index 4e99689ebe0c2..a78f7e8c80b94 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/ExpressionNodeInfo.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/ExpressionNodeInfo.cs
@@ -193,7 +193,7 @@ private bool TryGetStringValueFromUtf8Literal(out string? value)
 
         public bool IsBoolLiteral()
         {
-            return TryGetBoolValueFromLiteral(out var _);
+            return TryGetBoolValueFromLiteral(out _);
         }
     }
 }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/PropertyPattern.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/PropertyPattern.cs
index a195d9ffb8328..aa9d4eaea88dc 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/PropertyPattern.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/PropertyPattern.cs
@@ -25,7 +25,7 @@ private record AccessStep(string Identifier, Microsoft.CodeAnalysis.Location Loc
 
         private class AccessStepPack
         {
-            public readonly List<AccessStep> Prefix = new();
+            public List<AccessStep> Prefix { get; } = [];
             public AccessStep Last { get; private set; }
 
             public AccessStepPack Add(string identifier, Microsoft.CodeAnalysis.Location location)
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs
index 45228e8b81d8d..0d8d7df6c424a 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs
@@ -346,7 +346,7 @@ public virtual void Dispose()
         /// </summary>
         public void LogExtractorInfo()
         {
-            Logger.LogInfo($"  Extractor: {Environment.GetCommandLineArgs().First()}");
+            Logger.LogInfo($"  Extractor: {Environment.GetCommandLineArgs()[0]}");
             Logger.LogInfo($"  Extractor version: {Version}");
             Logger.LogInfo($"  Current working directory: {Directory.GetCurrentDirectory()}");
         }
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs
index a84a912d85ed9..c08721ea4b8ab 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs
@@ -34,7 +34,7 @@ public string? SkipReason
             private set;
         }
 
-        private static readonly Dictionary<string, string> knownCompilerNames = new Dictionary<string, string>
+        private static readonly Dictionary<string, string> knownCompilerNames = new()
         {
             { "csc.exe", "Microsoft" },
             { "csc2.exe", "Microsoft" },
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Context.cs b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Context.cs
index 57e9a5ca9f17a..654ce0cc0f503 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Context.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Extractor/Context.cs
@@ -68,7 +68,7 @@ internal void CacheLambdaParameterSymbol(IParameterSymbol param, SyntaxNode synt
             lambdaParameterCache[syntax] = param;
         }
 
-        private readonly Dictionary<SyntaxNode, IParameterSymbol> lambdaParameterCache = new Dictionary<SyntaxNode, IParameterSymbol>();
+        private readonly Dictionary<SyntaxNode, IParameterSymbol> lambdaParameterCache = [];
 
         /// <summary>
         /// The current compilation unit.
diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Populators/DirectiveVisitor.cs b/csharp/extractor/Semmle.Extraction.CSharp/Populators/DirectiveVisitor.cs
index b80d5175a8d19..f5f3c7d2acdf4 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Populators/DirectiveVisitor.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Populators/DirectiveVisitor.cs
@@ -8,7 +8,7 @@ namespace Semmle.Extraction.CSharp.Populators
     internal class DirectiveVisitor : CSharpSyntaxWalker
     {
         private readonly Context cx;
-        private readonly List<IEntity> branchesTaken = new();
+        private readonly List<IEntity> branchesTaken = [];
 
         /// <summary>
         /// Gets a list of `#if`, `#elif`, and `#else` entities where the branch
diff --git a/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs b/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
index 0f6683d329852..3c1b41f54bf1a 100644
--- a/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
+++ b/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
@@ -72,7 +72,7 @@ public void TestDotnetInfo()
             var dotnetCliInvoker = new DotNetCliInvokerStub(new List<string>());
 
             // Execute
-            var _ = MakeDotnet(dotnetCliInvoker);
+            _ = MakeDotnet(dotnetCliInvoker);
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
@@ -88,7 +88,7 @@ public void TestDotnetInfoFailure()
             // Execute
             try
             {
-                var _ = MakeDotnet(dotnetCliInvoker);
+                _ = MakeDotnet(dotnetCliInvoker);
             }
 
             // Verify
diff --git a/csharp/extractor/Semmle.Extraction/Context.cs b/csharp/extractor/Semmle.Extraction/Context.cs
index ec1ba53d08fce..8b7b750768c48 100644
--- a/csharp/extractor/Semmle.Extraction/Context.cs
+++ b/csharp/extractor/Semmle.Extraction/Context.cs
@@ -37,7 +37,7 @@ public class Context
         // A recursion guard against writing to the trap file whilst writing an id to the trap file.
         private bool writingLabel = false;
 
-        private readonly Queue<IEntity> labelQueue = new();
+        private readonly Queue<IEntity> labelQueue = [];
 
         protected void DefineLabel(IEntity entity)
         {
diff --git a/csharp/extractor/Semmle.Extraction/EscapingTextWriter.cs b/csharp/extractor/Semmle.Extraction/EscapingTextWriter.cs
index 6294ec3ffd310..2374b398843d7 100644
--- a/csharp/extractor/Semmle.Extraction/EscapingTextWriter.cs
+++ b/csharp/extractor/Semmle.Extraction/EscapingTextWriter.cs
@@ -56,7 +56,7 @@ private void WriteEscaped(char c)
                 default:
                     wrapped.Write(c);
                     break;
-            };
+            }
         }
 
         public void WriteSubId(IEntity entity)
diff --git a/csharp/extractor/Semmle.Extraction/Extractor/ExtractionContext.cs b/csharp/extractor/Semmle.Extraction/Extractor/ExtractionContext.cs
index 539b339f85c30..26b30ad004b2e 100644
--- a/csharp/extractor/Semmle.Extraction/Extractor/ExtractionContext.cs
+++ b/csharp/extractor/Semmle.Extraction/Extractor/ExtractionContext.cs
@@ -65,7 +65,7 @@ public void Message(Message msg)
 
         // Roslyn framework has no apparent mechanism to associate assemblies with their files.
         // So this lookup table needs to be populated.
-        private readonly Dictionary<string, string> referenceFilenames = new Dictionary<string, string>();
+        private readonly Dictionary<string, string> referenceFilenames = [];
 
         public void SetAssemblyFile(string assembly, string file)
         {
diff --git a/csharp/extractor/Semmle.Extraction/TrapWriter.cs b/csharp/extractor/Semmle.Extraction/TrapWriter.cs
index 6baf55f7647a3..53c98003ef57c 100644
--- a/csharp/extractor/Semmle.Extraction/TrapWriter.cs
+++ b/csharp/extractor/Semmle.Extraction/TrapWriter.cs
@@ -48,7 +48,7 @@ public TrapWriter(ILogger logger, PathTransformer.ITransformedPath outputfile, s
 
             writerLazy = new Lazy<StreamWriter>(() =>
             {
-                var tempPath = trap ?? FileUtils.GetTemporaryWorkingDirectory(out var _);
+                var tempPath = trap ?? FileUtils.GetTemporaryWorkingDirectory(out _);
 
                 do
                 {
diff --git a/csharp/extractor/Semmle.Util/EnvironmentVariables.cs b/csharp/extractor/Semmle.Util/EnvironmentVariables.cs
index 076507d07e0a2..1b0e40790ff18 100644
--- a/csharp/extractor/Semmle.Util/EnvironmentVariables.cs
+++ b/csharp/extractor/Semmle.Util/EnvironmentVariables.cs
@@ -45,7 +45,7 @@ public static bool GetBooleanOptOut(string name)
         public static bool GetBoolean(string name)
         {
             var env = Environment.GetEnvironmentVariable(name);
-            var _ = bool.TryParse(env, out var value);
+            _ = bool.TryParse(env, out var value);
             return value;
         }
 
diff --git a/csharp/extractor/Semmle.Util/Initializer.cs b/csharp/extractor/Semmle.Util/Initializer.cs
index 179c7efbe12ba..76d6b022de6ba 100644
--- a/csharp/extractor/Semmle.Util/Initializer.cs
+++ b/csharp/extractor/Semmle.Util/Initializer.cs
@@ -22,7 +22,7 @@ public Initializer(Action action)
 
         public void Run()
         {
-            var _ = doInit.Value;
+            _ = doInit.Value;
         }
     }
 }
diff --git a/csharp/extractor/Semmle.Util/MemoizedFunc.cs b/csharp/extractor/Semmle.Util/MemoizedFunc.cs
index f2018df8bb71f..d1a0edd3a4368 100644
--- a/csharp/extractor/Semmle.Util/MemoizedFunc.cs
+++ b/csharp/extractor/Semmle.Util/MemoizedFunc.cs
@@ -7,7 +7,7 @@ namespace Semmle.Util;
 public class MemoizedFunc<T1, T2> where T1 : notnull
 {
     private readonly Func<T1, T2> f;
-    private readonly Dictionary<T1, T2> cache = new();
+    private readonly Dictionary<T1, T2> cache = [];
 
     public MemoizedFunc(Func<T1, T2> f)
     {
@@ -28,7 +28,7 @@ public T2 Invoke(T1 s)
 public class ConcurrentMemoizedFunc<T1, T2> where T1 : notnull
 {
     private readonly Func<T1, T2> f;
-    private readonly ConcurrentDictionary<T1, T2> cache = new();
+    private readonly ConcurrentDictionary<T1, T2> cache = [];
 
     public ConcurrentMemoizedFunc(Func<T1, T2> f)
     {