diff --git a/src/Converters/PathConverters.cs b/src/Converters/PathConverters.cs
index dd7cfa49..1e321498 100644
--- a/src/Converters/PathConverters.cs
+++ b/src/Converters/PathConverters.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 
 using Avalonia.Data.Converters;
@@ -22,7 +22,7 @@ namespace SourceGit.Converters
                 var home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
                 var prefixLen = home.EndsWith('/') ? home.Length - 1 : home.Length;
                 if (v.StartsWith(home, StringComparison.Ordinal))
-                    return "~" + v.Substring(prefixLen);
+                    return $"~{v.Substring(prefixLen)}";
 
                 return v;
             });
diff --git a/src/Models/DiffResult.cs b/src/Models/DiffResult.cs
index e7d17994..baa9cf5f 100644
--- a/src/Models/DiffResult.cs
+++ b/src/Models/DiffResult.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Text.RegularExpressions;
 
@@ -147,9 +148,10 @@ namespace SourceGit.Models
         public void GenerateNewPatchFromSelection(Change change, string fileBlobGuid, TextDiffSelection selection, bool revert, string output)
         {
             var isTracked = !string.IsNullOrEmpty(fileBlobGuid);
-            var fileGuid = isTracked ? fileBlobGuid.Substring(0, 8) : "00000000";
 
-            var builder = new StringBuilder();
+            var fileGuid = isTracked ? fileBlobGuid.AsSpan().Slice(0, 8) : "00000000".AsSpan();
+
+            var builder = new StringBuilder(512);
             builder.Append("diff --git a/").Append(change.Path).Append(" b/").Append(change.Path).Append('\n');
             if (!revert && !isTracked)
                 builder.Append("new file mode 100644\n");
diff --git a/src/Models/Worktree.cs b/src/Models/Worktree.cs
index bc40e320..81f58545 100644
--- a/src/Models/Worktree.cs
+++ b/src/Models/Worktree.cs
@@ -1,4 +1,5 @@
-using CommunityToolkit.Mvvm.ComponentModel;
+using System;
+using CommunityToolkit.Mvvm.ComponentModel;
 
 namespace SourceGit.Models
 {
@@ -22,12 +23,12 @@ namespace SourceGit.Models
             get
             {
                 if (IsDetached)
-                    return $"deteched HEAD at {Head.Substring(10)}";
+                    return $"deteched HEAD at {Head.AsSpan().Slice(10)}";
 
-                if (Branch.StartsWith("refs/heads/", System.StringComparison.Ordinal))
+                if (Branch.StartsWith("refs/heads/", StringComparison.Ordinal))
                     return Branch.Substring(11);
 
-                if (Branch.StartsWith("refs/remotes/", System.StringComparison.Ordinal))
+                if (Branch.StartsWith("refs/remotes/", StringComparison.Ordinal))
                     return Branch.Substring(13);
 
                 return Branch;
diff --git a/src/ViewModels/Archive.cs b/src/ViewModels/Archive.cs
index 7ce0d968..a8a06e2c 100644
--- a/src/ViewModels/Archive.cs
+++ b/src/ViewModels/Archive.cs
@@ -1,4 +1,5 @@
-using System.ComponentModel.DataAnnotations;
+using System;
+using System.ComponentModel.DataAnnotations;
 using System.IO;
 using System.Threading.Tasks;
 
@@ -31,7 +32,7 @@ namespace SourceGit.ViewModels
         {
             _repo = repo;
             _revision = commit.SHA;
-            _saveFile = $"archive-{commit.SHA.Substring(0, 10)}.zip";
+            _saveFile = $"archive-{commit.SHA.AsSpan().Slice(0, 10)}.zip";
             BasedOn = commit;
         }
 
diff --git a/src/ViewModels/Blame.cs b/src/ViewModels/Blame.cs
index 7cfa8eac..b76db66d 100644
--- a/src/ViewModels/Blame.cs
+++ b/src/ViewModels/Blame.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 
 using Avalonia.Threading;
@@ -30,7 +31,7 @@ namespace SourceGit.ViewModels
         {
             _repo = repo;
 
-            Title = $"{file} @ {revision.Substring(0, 10)}";
+            Title = $"{file} @ {revision.AsSpan().Slice(0, 10)}";
             Task.Run(() =>
             {
                 var result = new Commands.Blame(repo, file, revision).Result();
diff --git a/src/ViewModels/Launcher.cs b/src/ViewModels/Launcher.cs
index 9ae99b33..2474a591 100644
--- a/src/ViewModels/Launcher.cs
+++ b/src/ViewModels/Launcher.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 
 using Avalonia.Collections;
@@ -584,7 +584,7 @@ namespace SourceGit.ViewModels
                     var home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
                     var prefixLen = home.EndsWith('/') ? home.Length - 1 : home.Length;
                     if (path.StartsWith(home, StringComparison.Ordinal))
-                        path = "~" + path.Substring(prefixLen);
+                        path = $"~{path.AsSpan().Slice(prefixLen)}";
                 }
 
                 Title = $"[{workspace}] {name} ({path})";
diff --git a/src/Views/Histories.axaml.cs b/src/Views/Histories.axaml.cs
index 84cfda2f..bab3f86e 100644
--- a/src/Views/Histories.axaml.cs
+++ b/src/Views/Histories.axaml.cs
@@ -196,7 +196,7 @@ namespace SourceGit.Views
                     foreach (var item in selected)
                     {
                         if (item is Models.Commit commit)
-                            builder.AppendLine($"{commit.SHA.Substring(0, 10)} - {commit.Subject}");
+                            builder.AppendLine($"{commit.SHA.AsSpan().Slice(0, 10)} - {commit.Subject}");
                     }
 
                     App.CopyText(builder.ToString());
diff --git a/src/Views/TextDiffView.axaml.cs b/src/Views/TextDiffView.axaml.cs
index ad2f8cea..d81addee 100644
--- a/src/Views/TextDiffView.axaml.cs
+++ b/src/Views/TextDiffView.axaml.cs
@@ -1047,7 +1047,8 @@ namespace SourceGit.Views
                 // The first selected line (partial selection)
                 if (i == startIdx && startPosition.Column > 1)
                 {
-                    builder.AppendLine(line.Content.Substring(startPosition.Column - 1));
+                    builder.Append(line.Content.AsSpan().Slice(startPosition.Column - 1));
+                    builder.Append(Environment.NewLine);
                     continue;
                 }
 
@@ -1061,7 +1062,14 @@ namespace SourceGit.Views
                 // For the last line (selection range is within original source)
                 if (i == endIdx)
                 {
-                    builder.Append(endPosition.Column - 1 < line.Content.Length ? line.Content.Substring(0, endPosition.Column - 1) : line.Content);
+                    if (endPosition.Column - 1 < line.Content.Length)
+                    {
+                        builder.Append(line.Content.AsSpan().Slice(0, endPosition.Column - 1));
+                    }
+                    else
+                    {
+                        builder.Append(line.Content);
+                    }
                     break;
                 }
 
@@ -1246,12 +1254,12 @@ namespace SourceGit.Views
             var textDiff = DataContext as Models.TextDiff;
             if (textDiff != null)
             {
-                var builder = new StringBuilder();
+                var builder = new StringBuilder(512);
                 foreach (var line in textDiff.Lines)
                 {
                     if (line.Content.Length > 10000)
                     {
-                        builder.Append(line.Content.Substring(0, 1000));
+                        builder.Append(line.Content.AsSpan().Slice(0, 1000));
                         builder.Append($"...({line.Content.Length - 1000} character trimmed)");
                     }
                     else