diff --git a/SongTidy.Tests/RenameValidatorTests.cs b/SongTidy.Tests/RenameValidatorTests.cs
new file mode 100644
index 0000000..a94defa
--- /dev/null
+++ b/SongTidy.Tests/RenameValidatorTests.cs
@@ -0,0 +1,370 @@
+using System.IO;
+using System.Linq;
+
+using SongTidy.Models;
+using SongTidy.Services;
+
+namespace SongTidy.Tests;
+
+/// <summary>
+/// Contains tests for <see cref="RenameValidator"/>.
+/// </summary>
+[TestClass]
+public sealed class RenameValidatorTests {
+    private string _tempDirectory = string.Empty;
+
+    /// <summary>
+    /// Creates a unique temporary directory for the current test.
+    /// </summary>
+    [TestInitialize]
+    public void Initialize() {
+        _tempDirectory = Path.Combine(Path.GetTempPath(), $"SongTidy Validation {Guid.NewGuid():N}");
+        Directory.CreateDirectory(_tempDirectory);
+    }
+
+    /// <summary>
+    /// Removes the temporary directory created for the current test.
+    /// </summary>
+    [TestCleanup]
+    public void Cleanup() {
+        Directory.Delete(_tempDirectory, recursive: true);
+    }
+
+    #region Per-entry validation
+
+    /// <summary>
+    /// Verifies that empty and whitespace-only titles are rejected.
+    /// </summary>
+    /// <param name="title">The title to validate.</param>
+    [TestMethod]
+    [DataRow("")]
+    [DataRow("   ")]
+    public void ReportsEmptyTitle(string title) {
+        string sourcePath = CreateFile("A.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, title));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.EmptyTitle, 1));
+    }
+
+    /// <summary>
+    /// Verifies that every forbidden file name character is detected in the title.
+    /// </summary>
+    /// <param name="invalidCharacter">The character to insert into the title.</param>
+    [TestMethod]
+    [DataRow("\\")]
+    [DataRow("/")]
+    [DataRow(":")]
+    [DataRow("*")]
+    [DataRow("?")]
+    [DataRow("\"")]
+    [DataRow("<")]
+    [DataRow(">")]
+    [DataRow("|")]
+    [DataRow("\t")]
+    public void ReportsInvalidCharacterInTitle(string invalidCharacter) {
+        string sourcePath = CreateFile("A.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "A" + invalidCharacter + "B"));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.InvalidFieldCharacter, 1));
+    }
+
+    /// <summary>
+    /// Verifies that invalid characters are detected in the artist and comment fields.
+    /// </summary>
+    [TestMethod]
+    public void ReportsInvalidCharactersInArtistAndComment() {
+        string sourcePath = CreateFile("A.mp3");
+
+        RenameValidationResult result = Validate(
+            CreateItem(sourcePath, "Title", artist: "A\\B", comment: "C:D"));
+
+        Assert.HasCount(
+            2,
+            result.Issues.Where(issue => issue.Problem == RenameValidationProblem.InvalidFieldCharacter));
+    }
+
+    /// <summary>
+    /// Verifies that target names ending with a dot or a space are rejected.
+    /// </summary>
+    /// <param name="title">The title that produces the invalid target ending.</param>
+    [TestMethod]
+    [DataRow("Title.")]
+    [DataRow("Title ")]
+    public void ReportsInvalidTargetEnding(string title) {
+        string sourcePath = CreateFile("Source");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, title));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.InvalidTargetEnding, 1));
+    }
+
+    /// <summary>
+    /// Verifies that missing source files are detected.
+    /// </summary>
+    [TestMethod]
+    public void ReportsMissingSourceFile() {
+        string sourcePath = Path.Combine(_tempDirectory, "Missing.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "Title"));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.MissingSourceFile, 1));
+    }
+
+    #endregion
+
+    #region Source path validation
+
+    /// <summary>
+    /// Verifies that duplicate source paths are reported for every affected row.
+    /// </summary>
+    [TestMethod]
+    public void ReportsDuplicateSourcePaths() {
+        string sourcePath = CreateFile("Dup.mp3");
+
+        RenameValidationResult result = Validate(
+            CreateItem(sourcePath, "One"),
+            CreateItem(sourcePath, "Two"));
+
+        Assert.HasCount(
+            2,
+            result.Issues.Where(issue => issue.Problem == RenameValidationProblem.DuplicateSourcePath));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateSourcePath, 1));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateSourcePath, 2));
+    }
+
+    /// <summary>
+    /// Verifies that source path comparison is case-sensitive.
+    /// </summary>
+    [TestMethod]
+    public void TreatsSourcePathsAsCaseSensitive() {
+        CreateFile("Case.mp3");
+        PlanItem first = CreateItem(Path.Combine(_tempDirectory, "Case.mp3"), "One");
+        PlanItem second = CreateItem(Path.Combine(_tempDirectory, "case.mp3"), "Two");
+
+        RenameValidationResult result = Validate(first, second);
+
+        Assert.IsFalse(
+            result.Issues.Any(issue => issue.Problem == RenameValidationProblem.DuplicateSourcePath));
+    }
+
+    #endregion
+
+    #region Target conflict validation
+
+    /// <summary>
+    /// Verifies that duplicate target paths are detected case-insensitively.
+    /// </summary>
+    [TestMethod]
+    public void ReportsDuplicateTargetNamesCaseInsensitively() {
+        string firstPath = CreateFile("A.mp3");
+        string secondPath = CreateFile("B.mp3");
+
+        RenameValidationResult result = Validate(
+            CreateItem(firstPath, "Same"),
+            CreateItem(secondPath, "same"));
+
+        Assert.HasCount(
+            2,
+            result.Issues.Where(issue => issue.Problem == RenameValidationProblem.DuplicateTargetName));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateTargetName, 1));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateTargetName, 2));
+    }
+
+    /// <summary>
+    /// Verifies that equal target names in different directories do not conflict.
+    /// </summary>
+    [TestMethod]
+    public void AllowsSameTargetNameInDifferentDirectories() {
+        string firstPath = CreateFile(Path.Combine("dir1", "A.mp3"));
+        string secondPath = CreateFile(Path.Combine("dir2", "B.mp3"));
+
+        RenameValidationResult result = Validate(
+            CreateItem(firstPath, "Same"),
+            CreateItem(secondPath, "Same"));
+
+        Assert.IsTrue(result.IsValid);
+    }
+
+    /// <summary>
+    /// Verifies that an existing target file is reported as a conflict.
+    /// </summary>
+    [TestMethod]
+    public void ReportsTargetFileConflict() {
+        string sourcePath = CreateFile("A.mp3");
+        CreateFile("Existing.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "Existing"));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.TargetFileConflict, 1));
+    }
+
+    /// <summary>
+    /// Verifies that a target equal to the entry's own source is not a conflict.
+    /// </summary>
+    [TestMethod]
+    public void AllowsTargetEqualToOwnSource() {
+        string sourcePath = CreateFile("A.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "A"));
+
+        Assert.IsTrue(result.IsValid);
+    }
+
+    /// <summary>
+    /// Verifies that casing-only changes to the entry's own source are not conflicts.
+    /// </summary>
+    [TestMethod]
+    public void AllowsTargetEqualToOwnSourceIgnoringCase() {
+        string sourcePath = CreateFile("A.mp3");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "a"));
+
+        Assert.IsTrue(result.IsValid);
+    }
+
+    /// <summary>
+    /// Verifies that a renaming chain such as A to B and B to A is blocked.
+    /// </summary>
+    [TestMethod]
+    public void BlocksConflictChain() {
+        string aPath = CreateFile("A.mp3");
+        string bPath = CreateFile("B.mp3");
+
+        RenameValidationResult result = Validate(
+            CreateItem(aPath, "B"),
+            CreateItem(bPath, "A"));
+
+        Assert.HasCount(
+            2,
+            result.Issues.Where(issue => issue.Problem == RenameValidationProblem.TargetFileConflict));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.TargetFileConflict, 1));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.TargetFileConflict, 2));
+    }
+
+    /// <summary>
+    /// Verifies that the original file extension is preserved when checking conflicts.
+    /// </summary>
+    [TestMethod]
+    public void UsesOriginalExtensionForTargetNames() {
+        string sourcePath = CreateFile("Source.flac");
+        CreateFile("Title.flac");
+
+        RenameValidationResult result = Validate(CreateItem(sourcePath, "Title"));
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.TargetFileConflict, 1));
+    }
+
+    /// <summary>
+    /// Verifies that the selected naming format controls the generated target name.
+    /// </summary>
+    [TestMethod]
+    public void UsesSelectedFormatForTargetNames() {
+        string sourcePath = CreateFile("A.mp3");
+        CreateFile("Title - Artist.mp3");
+        PlanItem item = CreateItem(sourcePath, "Title", artist: "Artist");
+
+        RenameValidationResult result = RenameValidator.Validate(
+            new[] { item },
+            RenameFormat.TitleFirst);
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.TargetFileConflict, 1));
+    }
+
+    #endregion
+
+    #region Combined validation
+
+    /// <summary>
+    /// Verifies that validation collects problems from multiple rules in one pass.
+    /// </summary>
+    [TestMethod]
+    public void ReportsAllProblemKinds() {
+        string sourcePath = CreateFile("A.mp3");
+        PlanItem emptyTitle = CreateItem(sourcePath, "");
+        PlanItem missingSource = CreateItem(Path.Combine(_tempDirectory, "Missing.mp3"), "Title");
+        PlanItem invalidCharacter = CreateItem(sourcePath, "Bad/Title");
+
+        RenameValidationResult result = Validate(emptyTitle, missingSource, invalidCharacter);
+
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.EmptyTitle, 1));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.MissingSourceFile, 2));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.InvalidFieldCharacter, 3));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateSourcePath, 1));
+        Assert.IsTrue(HasProblem(result, RenameValidationProblem.DuplicateSourcePath, 3));
+    }
+
+    /// <summary>
+    /// Verifies that a clean set of entries produces no issues.
+    /// </summary>
+    [TestMethod]
+    public void ReturnsValidResultForRenameableEntries() {
+        string firstPath = CreateFile("A.mp3");
+        string secondPath = CreateFile("B.mp3");
+
+        RenameValidationResult result = Validate(
+            CreateItem(firstPath, "One"),
+            CreateItem(secondPath, "Two"));
+
+        Assert.IsTrue(result.IsValid);
+        Assert.HasCount(0, result.Issues);
+    }
+
+    #endregion
+
+    /// <summary>
+    /// Creates an empty file inside the test directory.
+    /// </summary>
+    /// <param name="fileName">The relative file name, which may include a subdirectory.</param>
+    /// <returns>The full path of the created file.</returns>
+    private string CreateFile(string fileName) {
+        string path = Path.Combine(_tempDirectory, fileName);
+        string directory = Path.GetDirectoryName(path) ?? _tempDirectory;
+
+        Directory.CreateDirectory(directory);
+        File.WriteAllText(path, string.Empty);
+
+        return path;
+    }
+
+    /// <summary>
+    /// Creates a plan item with the supplied field values.
+    /// </summary>
+    /// <param name="path">The source file path.</param>
+    /// <param name="title">The title value.</param>
+    /// <param name="artist">The artist value.</param>
+    /// <param name="comment">The comment value.</param>
+    /// <returns>The created plan item.</returns>
+    private static PlanItem CreateItem(string path, string title, string artist = "", string comment = "") {
+        return new PlanItem {
+            Path = path,
+            Artist = artist,
+            Title = title,
+            Comment = comment,
+        };
+    }
+
+    /// <summary>
+    /// Validates entries with the artist-first format.
+    /// </summary>
+    /// <param name="items">The entries to validate.</param>
+    /// <returns>The validation result.</returns>
+    private static RenameValidationResult Validate(params PlanItem[] items) {
+        return RenameValidator.Validate(items, RenameFormat.ArtistFirst);
+    }
+
+    /// <summary>
+    /// Determines whether the result contains a specific problem for a row.
+    /// </summary>
+    /// <param name="result">The validation result to inspect.</param>
+    /// <param name="problem">The problem category to find.</param>
+    /// <param name="rowNumber">The one-based row number to match.</param>
+    /// <returns><see langword="true"/> when the problem is present.</returns>
+    private static bool HasProblem(
+        RenameValidationResult result,
+        RenameValidationProblem problem,
+        int rowNumber) {
+        return result.Issues.Any(issue => issue.Problem == problem && issue.RowNumber == rowNumber);
+    }
+}
diff --git a/SongTidy/Services/RenameValidator.cs b/SongTidy/Services/RenameValidator.cs
new file mode 100644
index 0000000..6050592
--- /dev/null
+++ b/SongTidy/Services/RenameValidator.cs
@@ -0,0 +1,337 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+using SongTidy.Models;
+
+namespace SongTidy.Services;
+
+/// <summary>
+/// Identifies the category of a rename validation problem.
+/// </summary>
+public enum RenameValidationProblem {
+    /// <summary>
+    /// The title is empty or contains only whitespace.
+    /// </summary>
+    EmptyTitle,
+
+    /// <summary>
+    /// An editable field contains a character that cannot appear in a file name.
+    /// </summary>
+    InvalidFieldCharacter,
+
+    /// <summary>
+    /// The generated target name ends with a dot or a space.
+    /// </summary>
+    InvalidTargetEnding,
+
+    /// <summary>
+    /// The source file no longer exists.
+    /// </summary>
+    MissingSourceFile,
+
+    /// <summary>
+    /// The same source path appears more than once.
+    /// </summary>
+    DuplicateSourcePath,
+
+    /// <summary>
+    /// Multiple entries generate the same target path.
+    /// </summary>
+    DuplicateTargetName,
+
+    /// <summary>
+    /// The target path already exists on disk under a different source path.
+    /// </summary>
+    TargetFileConflict,
+}
+
+/// <summary>
+/// Represents one validation problem associated with a plan row.
+/// </summary>
+/// <param name="RowNumber">The one-based row number of the affected entry.</param>
+/// <param name="Problem">The problem category.</param>
+/// <param name="Message">The user-facing reason for the problem.</param>
+public sealed record RenameValidationIssue(int RowNumber, RenameValidationProblem Problem, string Message);
+
+/// <summary>
+/// Contains the complete result of a rename validation pass.
+/// </summary>
+/// <param name="Issues">All problems found during validation.</param>
+public sealed record RenameValidationResult(IReadOnlyList<RenameValidationIssue> Issues) {
+    /// <summary>
+    /// Gets a value indicating whether validation found no problems.
+    /// </summary>
+    public bool IsValid => Issues.Count == 0;
+}
+
+/// <summary>
+/// Validates that a set of plan entries can be renamed without conflicts.
+/// </summary>
+public static class RenameValidator {
+    #region Public API
+
+    /// <summary>
+    /// Validates all entries and returns every problem found.
+    /// </summary>
+    /// <param name="items">The entries to validate.</param>
+    /// <param name="format">The naming format used to generate target names.</param>
+    /// <returns>All validation problems, or an empty result when renaming can proceed.</returns>
+    public static RenameValidationResult Validate(IReadOnlyList<PlanItem> items, RenameFormat format) {
+        List<RenameValidationIssue> issues = new();
+        List<EntryTarget> targets = CreateTargets(items, format);
+
+        // Check rules that apply to each entry independently.
+        AddEntryIssues(items, targets, issues);
+
+        // Check rules that require comparing entries with each other or with the file system.
+        AddDuplicateSourceIssues(items, issues);
+        AddDuplicateTargetIssues(targets, issues);
+        AddDiskConflictIssues(items, targets, issues);
+
+        // Present problems in row order so the report reads naturally.
+        issues.Sort(static (left, right) => left.RowNumber.CompareTo(right.RowNumber));
+
+        return new RenameValidationResult(issues);
+    }
+
+    #endregion
+
+    #region Target generation
+
+    /// <summary>
+    /// Generates target names and full target paths for every entry.
+    /// </summary>
+    /// <param name="items">The entries to process.</param>
+    /// <param name="format">The naming format to apply.</param>
+    /// <returns>The generated targets in entry order.</returns>
+    private static List<EntryTarget> CreateTargets(IReadOnlyList<PlanItem> items, RenameFormat format) {
+        List<EntryTarget> targets = new(items.Count);
+
+        for (int index = 0; index < items.Count; index++) {
+            PlanItem item = items[index];
+            string fileName = RenameFormats.GenerateStem(format, item.Artist, item.Title, item.Comment)
+                + Path.GetExtension(item.Path);
+            string directory = Path.GetDirectoryName(item.Path) ?? string.Empty;
+            string path = Path.Combine(directory, fileName);
+
+            targets.Add(new EntryTarget(index + 1, fileName, path));
+        }
+
+        return targets;
+    }
+
+    #endregion
+
+    #region Per-entry validation
+
+    /// <summary>
+    /// Checks the rules that can be evaluated for one entry at a time.
+    /// </summary>
+    /// <param name="items">The entries to validate.</param>
+    /// <param name="targets">The generated targets in entry order.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddEntryIssues(
+        IReadOnlyList<PlanItem> items,
+        List<EntryTarget> targets,
+        List<RenameValidationIssue> issues) {
+        for (int index = 0; index < items.Count; index++) {
+            PlanItem item = items[index];
+            EntryTarget target = targets[index];
+            int rowNumber = target.RowNumber;
+
+            // The title is mandatory.
+            if (string.IsNullOrWhiteSpace(item.Title)) {
+                issues.Add(new RenameValidationIssue(
+                    rowNumber,
+                    RenameValidationProblem.EmptyTitle,
+                    "The title is empty."));
+            }
+
+            AddInvalidCharacterIssues(item, rowNumber, issues);
+
+            // Windows cannot create names that end with a dot or a space.
+            if (target.FileName.EndsWith('.') || target.FileName.EndsWith(' ')) {
+                issues.Add(new RenameValidationIssue(
+                    rowNumber,
+                    RenameValidationProblem.InvalidTargetEnding,
+                    "The target file name cannot end with a dot or a space."));
+            }
+
+            // The source file must still exist when the user confirms renaming.
+            if (!File.Exists(item.Path)) {
+                issues.Add(new RenameValidationIssue(
+                    rowNumber,
+                    RenameValidationProblem.MissingSourceFile,
+                    "The source file does not exist."));
+            }
+        }
+    }
+
+    /// <summary>
+    /// Checks all editable fields for characters that cannot appear in a file name.
+    /// </summary>
+    /// <param name="item">The entry to inspect.</param>
+    /// <param name="rowNumber">The one-based row number.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddInvalidCharacterIssues(
+        PlanItem item,
+        int rowNumber,
+        List<RenameValidationIssue> issues) {
+        AddFieldCharacterIssue(item.Artist, "Artist", rowNumber, issues);
+        AddFieldCharacterIssue(item.Title, "Title", rowNumber, issues);
+        AddFieldCharacterIssue(item.Comment, "Comment", rowNumber, issues);
+    }
+
+    /// <summary>
+    /// Adds one issue when a field contains an invalid file name character.
+    /// </summary>
+    /// <param name="value">The field value to inspect.</param>
+    /// <param name="fieldName">The localized field name used in the message.</param>
+    /// <param name="rowNumber">The one-based row number.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddFieldCharacterIssue(
+        string value,
+        string fieldName,
+        int rowNumber,
+        List<RenameValidationIssue> issues) {
+        foreach (char character in value) {
+            if (IsInvalidFileNameCharacter(character)) {
+                issues.Add(new RenameValidationIssue(
+                    rowNumber,
+                    RenameValidationProblem.InvalidFieldCharacter,
+                    $"{fieldName} contains a character that is not allowed in a file name."));
+                return;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Determines whether a character is forbidden in a Windows file name.
+    /// </summary>
+    /// <param name="character">The character to inspect.</param>
+    /// <returns><see langword="true"/> when the character is invalid.</returns>
+    private static bool IsInvalidFileNameCharacter(char character) {
+        return char.IsControl(character)
+            || character is '\\' or '/' or ':' or '*' or '?' or '"' or '<' or '>' or '|';
+    }
+
+    #endregion
+
+    #region Conflict validation
+
+    /// <summary>
+    /// Adds issues for source paths that appear more than once.
+    /// </summary>
+    /// <param name="items">The entries to inspect.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddDuplicateSourceIssues(
+        IReadOnlyList<PlanItem> items,
+        List<RenameValidationIssue> issues) {
+        Dictionary<string, List<int>> rowsByPath = new(StringComparer.Ordinal);
+
+        // Group rows by exact source path; comparison is intentionally case-sensitive.
+        for (int index = 0; index < items.Count; index++) {
+            string path = items[index].Path;
+
+            if (!rowsByPath.TryGetValue(path, out List<int>? rows)) {
+                rows = new List<int>();
+                rowsByPath.Add(path, rows);
+            }
+
+            rows.Add(index + 1);
+        }
+
+        // Report every row that participates in a duplicate group.
+        foreach (List<int> rows in rowsByPath.Values) {
+            if (rows.Count < 2) {
+                continue;
+            }
+
+            foreach (int rowNumber in rows) {
+                issues.Add(new RenameValidationIssue(
+                    rowNumber,
+                    RenameValidationProblem.DuplicateSourcePath,
+                    "The source path duplicates another entry in the list."));
+            }
+        }
+    }
+
+    /// <summary>
+    /// Adds issues for entries that generate the same target path.
+    /// </summary>
+    /// <param name="targets">The generated targets to inspect.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddDuplicateTargetIssues(
+        List<EntryTarget> targets,
+        List<RenameValidationIssue> issues) {
+        Dictionary<string, List<EntryTarget>> groups = new(StringComparer.OrdinalIgnoreCase);
+
+        // Group entries by full target path; file systems treat casing as equivalent.
+        foreach (EntryTarget target in targets) {
+            if (!groups.TryGetValue(target.Path, out List<EntryTarget>? group)) {
+                group = new List<EntryTarget>();
+                groups.Add(target.Path, group);
+            }
+
+            group.Add(target);
+        }
+
+        // Report every entry that participates in a duplicate target group.
+        foreach (List<EntryTarget> group in groups.Values) {
+            if (group.Count < 2) {
+                continue;
+            }
+
+            foreach (EntryTarget target in group) {
+                issues.Add(new RenameValidationIssue(
+                    target.RowNumber,
+                    RenameValidationProblem.DuplicateTargetName,
+                    $"The target file name duplicates another entry: {target.FileName}"));
+            }
+        }
+    }
+
+    /// <summary>
+    /// Adds issues for targets that already exist under a different source path.
+    /// </summary>
+    /// <param name="items">The entries to inspect.</param>
+    /// <param name="targets">The generated targets in entry order.</param>
+    /// <param name="issues">The issue collection to append to.</param>
+    private static void AddDiskConflictIssues(
+        IReadOnlyList<PlanItem> items,
+        List<EntryTarget> targets,
+        List<RenameValidationIssue> issues) {
+        for (int index = 0; index < items.Count; index++) {
+            PlanItem item = items[index];
+            EntryTarget target = targets[index];
+
+            // Renaming a file to itself is not a conflict, even when only casing changes.
+            if (string.Equals(target.Path, item.Path, StringComparison.OrdinalIgnoreCase)) {
+                continue;
+            }
+
+            // Any other existing target would be overwritten or would block the rename.
+            if (File.Exists(target.Path)) {
+                issues.Add(new RenameValidationIssue(
+                    target.RowNumber,
+                    RenameValidationProblem.TargetFileConflict,
+                    $"The target file already exists: {target.FileName}"));
+            }
+        }
+    }
+
+    #endregion
+
+    #region Nested types
+
+    /// <summary>
+    /// Represents a generated target name for one plan entry.
+    /// </summary>
+    /// <param name="RowNumber">The one-based row number of the entry.</param>
+    /// <param name="FileName">The target file name including its original extension.</param>
+    /// <param name="Path">The full target path in the source directory.</param>
+    private sealed record EntryTarget(int RowNumber, string FileName, string Path);
+
+    #endregion
+}