diff --git a/src/EchoHub.Tests/ChatLineTests.cs b/src/EchoHub.Tests/ChatLineTests.cs
new file mode 100644
index 0000000..16abab5
--- /dev/null
+++ b/src/EchoHub.Tests/ChatLineTests.cs
@@ -0,0 +1,107 @@
+using EchoHub.Client.UI;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+/// <summary>
+/// Tests for static string-utility methods on ChatLine.
+/// Note: Tests that construct ChatLine/ChatListSource or use Terminal.Gui types
+/// (Attribute, Color) are excluded because Terminal.Gui's module initializer
+/// requires a display driver which is unavailable in CI/test environments.
+/// </summary>
+public class ChatLineTests
+{
+    // ── HasColorTags ──────────────────────────────────────────────────
+
+    [Fact]
+    public void HasColorTags_ForegroundTag_ReturnsTrue()
+    {
+        Assert.True(ChatLine.HasColorTags("Hello {F:FF0000}world"));
+    }
+
+    [Fact]
+    public void HasColorTags_BackgroundTag_ReturnsTrue()
+    {
+        Assert.True(ChatLine.HasColorTags("Hello {B:00FF00}world"));
+    }
+
+    [Fact]
+    public void HasColorTags_ResetTag_ReturnsTrue()
+    {
+        Assert.True(ChatLine.HasColorTags("Hello{X}"));
+    }
+
+    [Fact]
+    public void HasColorTags_NoTags_ReturnsFalse()
+    {
+        Assert.False(ChatLine.HasColorTags("Hello world"));
+    }
+
+    [Fact]
+    public void HasColorTags_PartialTag_ReturnsFalse()
+    {
+        // {Z:...} is not a valid tag (only F or B)
+        Assert.False(ChatLine.HasColorTags("Hello {Z:000000}"));
+    }
+
+    [Fact]
+    public void HasColorTags_EmptyString_ReturnsFalse()
+    {
+        Assert.False(ChatLine.HasColorTags(""));
+    }
+
+    [Theory]
+    [InlineData("{F:AABBCC}text")]
+    [InlineData("prefix{B:112233}suffix")]
+    [InlineData("a{X}b")]
+    [InlineData("{F:000000}{B:FFFFFF}{X}")]
+    public void HasColorTags_VariousValidTags_ReturnsTrue(string input)
+    {
+        Assert.True(ChatLine.HasColorTags(input));
+    }
+
+    // ── StripColorTags ────────────────────────────────────────────────
+
+    [Fact]
+    public void StripColorTags_RemovesAllTags()
+    {
+        var result = ChatLine.StripColorTags("{F:FF0000}red{B:00FF00}green{X}");
+        Assert.Equal("redgreen", result);
+    }
+
+    [Fact]
+    public void StripColorTags_NoTags_ReturnsOriginal()
+    {
+        var result = ChatLine.StripColorTags("plain text");
+        Assert.Equal("plain text", result);
+    }
+
+    [Fact]
+    public void StripColorTags_OnlyTags_ReturnsEmpty()
+    {
+        var result = ChatLine.StripColorTags("{F:AABBCC}{B:112233}{X}");
+        Assert.Equal("", result);
+    }
+
+    [Fact]
+    public void StripColorTags_MixedContent_KeepsText()
+    {
+        var result = ChatLine.StripColorTags("before{F:FF0000}middle{X}after");
+        Assert.Equal("beforemiddleafter", result);
+    }
+
+    [Fact]
+    public void StripColorTags_MultipleConsecutiveTags_AllStripped()
+    {
+        var result = ChatLine.StripColorTags("{F:FF0000}{B:00FF00}{X}{F:0000FF}text{X}");
+        Assert.Equal("text", result);
+    }
+
+    [Fact]
+    public void StripColorTags_PreservesNonTagBraces()
+    {
+        // {Hello} is not a valid tag and should be preserved
+        var result = ChatLine.StripColorTags("{Hello} world");
+        Assert.Equal("{Hello} world", result);
+    }
+}
diff --git a/src/EchoHub.Tests/CommandHandlerTests.cs b/src/EchoHub.Tests/CommandHandlerTests.cs
new file mode 100644
index 0000000..5c58bf7
--- /dev/null
+++ b/src/EchoHub.Tests/CommandHandlerTests.cs
@@ -0,0 +1,462 @@
+using EchoHub.Client.Commands;
+using EchoHub.Core.Models;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class CommandHandlerTests
+{
+    private CommandHandler CreateHandler() => new();
+
+    // ── IsCommand ─────────────────────────────────────────────────────
+
+    [Fact]
+    public void IsCommand_StartsWithSlash_ReturnsTrue()
+    {
+        var handler = CreateHandler();
+        Assert.True(handler.IsCommand("/help"));
+    }
+
+    [Fact]
+    public void IsCommand_NoSlash_ReturnsFalse()
+    {
+        var handler = CreateHandler();
+        Assert.False(handler.IsCommand("hello"));
+    }
+
+    [Fact]
+    public void IsCommand_EmptyString_ReturnsFalse()
+    {
+        var handler = CreateHandler();
+        Assert.False(handler.IsCommand(""));
+    }
+
+    // ── HandleAsync — not a command ───────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_NotCommand_ReturnsFalse()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("hello world");
+
+        Assert.False(result.Handled);
+    }
+
+    // ── HandleAsync — unknown command ─────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_UnknownCommand_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/doesnotexist");
+
+        Assert.True(result.Handled);
+        Assert.True(result.IsError);
+        Assert.Contains("Unknown command", result.Message);
+    }
+
+    // ── /status ───────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_StatusOnline_SetsOnlineStatus()
+    {
+        var handler = CreateHandler();
+        UserStatus? capturedStatus = null;
+        handler.OnSetStatus += (status, msg) => { capturedStatus = status; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/status online");
+
+        Assert.True(result.Handled);
+        Assert.False(result.IsError);
+        Assert.Equal(UserStatus.Online, capturedStatus);
+    }
+
+    [Fact]
+    public async Task HandleAsync_StatusAway_SetsAwayStatus()
+    {
+        var handler = CreateHandler();
+        UserStatus? capturedStatus = null;
+        handler.OnSetStatus += (status, msg) => { capturedStatus = status; return Task.CompletedTask; };
+
+        await handler.HandleAsync("/status away");
+        Assert.Equal(UserStatus.Away, capturedStatus);
+    }
+
+    [Fact]
+    public async Task HandleAsync_StatusCustomMessage_SetsStatusMessage()
+    {
+        var handler = CreateHandler();
+        string? capturedMessage = null;
+        handler.OnSetStatus += (status, msg) => { capturedMessage = msg; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/status brb lunch");
+
+        Assert.True(result.Handled);
+        Assert.Contains("brb lunch", result.Message);
+        Assert.Equal("brb lunch", capturedMessage);
+    }
+
+    [Fact]
+    public async Task HandleAsync_StatusNoArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/status");
+
+        Assert.True(result.IsError);
+        Assert.Contains("Usage", result.Message);
+    }
+
+    // ── /nick ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Nick_SetsDisplayName()
+    {
+        var handler = CreateHandler();
+        string? capturedNick = null;
+        handler.OnSetNick += nick => { capturedNick = nick; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/nick Bob Smith");
+
+        Assert.True(result.Handled);
+        Assert.Equal("Bob Smith", capturedNick);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Nick_EmptyArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/nick");
+
+        Assert.True(result.IsError);
+        Assert.Contains("Usage", result.Message);
+    }
+
+    // ── /color ────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Color_ValidHex_Succeeds()
+    {
+        var handler = CreateHandler();
+        string? capturedColor = null;
+        handler.OnSetColor += color => { capturedColor = color; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/color #FF5733");
+
+        Assert.True(result.Handled);
+        Assert.False(result.IsError);
+        Assert.Equal("#FF5733", capturedColor);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Color_WithoutHash_AddsHash()
+    {
+        var handler = CreateHandler();
+        string? capturedColor = null;
+        handler.OnSetColor += color => { capturedColor = color; return Task.CompletedTask; };
+
+        await handler.HandleAsync("/color FF5733");
+        Assert.Equal("#FF5733", capturedColor);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Color_InvalidHex_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/color #ZZZZZZ");
+
+        Assert.True(result.IsError);
+        Assert.Contains("Invalid color", result.Message);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Color_TooShort_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/color #FFF");
+
+        Assert.True(result.IsError);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Color_NoArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/color");
+
+        Assert.True(result.IsError);
+    }
+
+    // ── /join ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Join_StripsHashPrefix()
+    {
+        var handler = CreateHandler();
+        string? capturedChannel = null;
+        handler.OnJoinChannel += ch => { capturedChannel = ch; return Task.CompletedTask; };
+
+        await handler.HandleAsync("/join #random");
+        Assert.Equal("random", capturedChannel);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Join_NoHash_PassedDirectly()
+    {
+        var handler = CreateHandler();
+        string? capturedChannel = null;
+        handler.OnJoinChannel += ch => { capturedChannel = ch; return Task.CompletedTask; };
+
+        await handler.HandleAsync("/join random");
+        Assert.Equal("random", capturedChannel);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Join_NoArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/join");
+
+        Assert.True(result.IsError);
+    }
+
+    // ── /kick ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Kick_WithReason_ParsesUsernameAndReason()
+    {
+        var handler = CreateHandler();
+        string? capturedUser = null;
+        string? capturedReason = null;
+        handler.OnKickUser += (user, reason) =>
+        {
+            capturedUser = user;
+            capturedReason = reason;
+            return Task.CompletedTask;
+        };
+
+        await handler.HandleAsync("/kick baduser being rude");
+        Assert.Equal("baduser", capturedUser);
+        Assert.Equal("being rude", capturedReason);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Kick_WithoutReason_NullReason()
+    {
+        var handler = CreateHandler();
+        string? capturedReason = "initial";
+        handler.OnKickUser += (user, reason) =>
+        {
+            capturedReason = reason;
+            return Task.CompletedTask;
+        };
+
+        await handler.HandleAsync("/kick baduser");
+        Assert.Null(capturedReason);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Kick_NoArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/kick");
+        Assert.True(result.IsError);
+    }
+
+    // ── /mute ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Mute_WithDuration_ParsesDuration()
+    {
+        var handler = CreateHandler();
+        int? capturedDuration = null;
+        handler.OnMuteUser += (user, duration) =>
+        {
+            capturedDuration = duration;
+            return Task.CompletedTask;
+        };
+
+        await handler.HandleAsync("/mute alice 30");
+        Assert.Equal(30, capturedDuration);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Mute_WithoutDuration_NullDuration()
+    {
+        var handler = CreateHandler();
+        int? capturedDuration = -1;
+        handler.OnMuteUser += (user, duration) =>
+        {
+            capturedDuration = duration;
+            return Task.CompletedTask;
+        };
+
+        await handler.HandleAsync("/mute alice");
+        Assert.Null(capturedDuration);
+    }
+
+    // ── /role ─────────────────────────────────────────────────────────
+
+    [Theory]
+    [InlineData("admin")]
+    [InlineData("mod")]
+    [InlineData("member")]
+    public async Task HandleAsync_Role_ValidRole_Succeeds(string role)
+    {
+        var handler = CreateHandler();
+        string? capturedRole = null;
+        handler.OnAssignRole += (user, r) => { capturedRole = r; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync($"/role alice {role}");
+
+        Assert.True(result.Handled);
+        Assert.False(result.IsError);
+        Assert.Equal(role, capturedRole);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Role_InvalidRole_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/role alice superadmin");
+
+        Assert.True(result.IsError);
+        Assert.Contains("Invalid role", result.Message);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Role_MissingRole_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/role alice");
+
+        Assert.True(result.IsError);
+    }
+
+    // ── /send ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Send_NoArgs_ReturnsUsageError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/send");
+
+        Assert.True(result.IsError);
+        Assert.Contains("Usage", result.Message);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Send_UrlInput_RecognizedAsUrl()
+    {
+        var handler = CreateHandler();
+        string? capturedTarget = null;
+        handler.OnSendFile += (target, size) => { capturedTarget = target; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/send https://example.com/image.png");
+
+        Assert.True(result.Handled);
+        Assert.False(result.IsError);
+        Assert.Equal("https://example.com/image.png", capturedTarget);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Send_UrlWithSizeFlag_ExtractsSizeCorrectly()
+    {
+        var handler = CreateHandler();
+        string? capturedSize = null;
+        handler.OnSendFile += (target, size) => { capturedSize = size; return Task.CompletedTask; };
+
+        await handler.HandleAsync("/send https://example.com/photo.jpg -s");
+        Assert.Equal("s", capturedSize);
+    }
+
+    // ── /help ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Help_ReturnsHelpText()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/help");
+
+        Assert.True(result.Handled);
+        Assert.Contains("Available commands", result.Message);
+    }
+
+    [Fact]
+    public async Task HandleAsync_QuestionMark_ReturnsHelp()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/?");
+
+        Assert.True(result.Handled);
+        Assert.Contains("Available commands", result.Message);
+    }
+
+    // ── /ban ──────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Ban_WithReason_ParsesUsernameAndReason()
+    {
+        var handler = CreateHandler();
+        string? capturedUser = null;
+        string? capturedReason = null;
+        handler.OnBanUser += (user, reason) =>
+        {
+            capturedUser = user;
+            capturedReason = reason;
+            return Task.CompletedTask;
+        };
+
+        await handler.HandleAsync("/ban troll spamming links");
+        Assert.Equal("troll", capturedUser);
+        Assert.Equal("spamming links", capturedReason);
+    }
+
+    // ── /topic ────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Topic_SetsTopic()
+    {
+        var handler = CreateHandler();
+        string? capturedTopic = null;
+        handler.OnSetTopic += topic => { capturedTopic = topic; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/topic Welcome to our channel!");
+
+        Assert.True(result.Handled);
+        Assert.Equal("Welcome to our channel!", capturedTopic);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Topic_NoArgs_ReturnsError()
+    {
+        var handler = CreateHandler();
+        var result = await handler.HandleAsync("/topic");
+        Assert.True(result.IsError);
+    }
+
+    // ── /quit and /exit ───────────────────────────────────────────────
+
+    [Fact]
+    public async Task HandleAsync_Quit_Handled()
+    {
+        var handler = CreateHandler();
+        var quitCalled = false;
+        handler.OnQuit += () => { quitCalled = true; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/quit");
+        Assert.True(result.Handled);
+        Assert.True(quitCalled);
+    }
+
+    [Fact]
+    public async Task HandleAsync_Exit_Handled()
+    {
+        var handler = CreateHandler();
+        var quitCalled = false;
+        handler.OnQuit += () => { quitCalled = true; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync("/exit");
+        Assert.True(result.Handled);
+        Assert.True(quitCalled);
+    }
+}
diff --git a/src/EchoHub.Tests/DataMigrationServiceTests.cs b/src/EchoHub.Tests/DataMigrationServiceTests.cs
new file mode 100644
index 0000000..31c2198
--- /dev/null
+++ b/src/EchoHub.Tests/DataMigrationServiceTests.cs
@@ -0,0 +1,74 @@
+using EchoHub.Server.Setup;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class DataMigrationServiceTests
+{
+    // ── AnsiToColorTags ───────────────────────────────────────────────
+
+    [Fact]
+    public void AnsiToColorTags_ForegroundEscape_ConvertedToColorTag()
+    {
+        var ansi = "\x1b[38;2;255;0;0mred text";
+        var result = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal("{F:FF0000}red text", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_BackgroundEscape_ConvertedToColorTag()
+    {
+        var ansi = "\x1b[48;2;0;255;0mgreen bg";
+        var result = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal("{B:00FF00}green bg", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_ResetEscape_ConvertedToResetTag()
+    {
+        var ansi = "\x1b[0m";
+        var result = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal("{X}", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_NoEscapes_ReturnsUnchanged()
+    {
+        var text = "Hello, world!";
+        var result = DataMigrationService.AnsiToColorTags(text);
+
+        Assert.Equal("Hello, world!", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_MixedContent_ConvertsEscapesOnly()
+    {
+        var ansi = "before\x1b[38;2;100;200;50mtextafter";
+        var result = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal("before{F:64C832}textafter", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_MultipleTags_AllConverted()
+    {
+        var ansi = "\x1b[38;2;255;0;0mred\x1b[48;2;0;0;255mblue bg\x1b[0mreset";
+        var result = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal("{F:FF0000}red{B:0000FF}blue bg{X}reset", result);
+    }
+
+    [Fact]
+    public void AnsiToColorTags_RoundTrip_WithColorTagsToAnsi()
+    {
+        // AnsiToColorTags and IrcMessageFormatter.ColorTagsToAnsi should be inverses
+        var original = "{F:FF0000}red{B:00FF00}green{X}";
+        var ansi = EchoHub.Server.Irc.IrcMessageFormatter.ColorTagsToAnsi(original);
+        var backToTags = DataMigrationService.AnsiToColorTags(ansi);
+
+        Assert.Equal(original, backToTags);
+    }
+}
diff --git a/src/EchoHub.Tests/EchoHub.Tests.csproj b/src/EchoHub.Tests/EchoHub.Tests.csproj
index 1a9b2a8..c3d45b4 100644
--- a/src/EchoHub.Tests/EchoHub.Tests.csproj
+++ b/src/EchoHub.Tests/EchoHub.Tests.csproj
@@ -21,6 +21,7 @@
     <ProjectReference Include="..\EchoHub.Client\EchoHub.Client.csproj" />
     <ProjectReference Include="..\EchoHub.Core\EchoHub.Core.csproj" />
     <ProjectReference Include="..\EchoHub.Server\EchoHub.Server.csproj" />
+    <ProjectReference Include="..\EchoHub.Server.Irc\EchoHub.Server.Irc.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/EchoHub.Tests/FileValidationHelperTests.cs b/src/EchoHub.Tests/FileValidationHelperTests.cs
index 4a0c3eb..59bc283 100644
--- a/src/EchoHub.Tests/FileValidationHelperTests.cs
+++ b/src/EchoHub.Tests/FileValidationHelperTests.cs
@@ -53,4 +53,48 @@ public class FileValidationHelperTests
         FileValidationHelper.IsValidImage(stream);
         Assert.Equal(0, stream.Position);
     }
+
+    // ── IsAudioFile tests ─────────────────────────────────────────────
+
+    [Theory]
+    [InlineData("song.mp3")]
+    [InlineData("track.wav")]
+    [InlineData("audio.ogg")]
+    [InlineData("music.flac")]
+    [InlineData("clip.aac")]
+    [InlineData("podcast.m4a")]
+    [InlineData("old.wma")]
+    public void IsAudioFile_SupportedExtensions_ReturnsTrue(string fileName)
+    {
+        Assert.True(FileValidationHelper.IsAudioFile(fileName));
+    }
+
+    [Theory]
+    [InlineData("song.MP3")]
+    [InlineData("track.Wav")]
+    [InlineData("audio.OGG")]
+    [InlineData("music.FLAC")]
+    public void IsAudioFile_CaseInsensitive_ReturnsTrue(string fileName)
+    {
+        Assert.True(FileValidationHelper.IsAudioFile(fileName));
+    }
+
+    [Theory]
+    [InlineData("document.txt")]
+    [InlineData("report.pdf")]
+    [InlineData("app.exe")]
+    [InlineData("photo.jpg")]
+    [InlineData("image.png")]
+    public void IsAudioFile_NonAudioExtension_ReturnsFalse(string fileName)
+    {
+        Assert.False(FileValidationHelper.IsAudioFile(fileName));
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("noextension")]
+    public void IsAudioFile_EmptyOrNoExtension_ReturnsFalse(string fileName)
+    {
+        Assert.False(FileValidationHelper.IsAudioFile(fileName));
+    }
 }
diff --git a/src/EchoHub.Tests/ImageToAsciiServiceTests.cs b/src/EchoHub.Tests/ImageToAsciiServiceTests.cs
new file mode 100644
index 0000000..9e9238c
--- /dev/null
+++ b/src/EchoHub.Tests/ImageToAsciiServiceTests.cs
@@ -0,0 +1,62 @@
+using EchoHub.Core.Constants;
+using EchoHub.Server.Services;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class ImageToAsciiServiceTests
+{
+    [Fact]
+    public void GetDimensions_Small_Returns40x40()
+    {
+        var (w, h) = ImageToAsciiService.GetDimensions("s");
+        Assert.Equal(40, w);
+        Assert.Equal(40, h);
+    }
+
+    [Fact]
+    public void GetDimensions_Large_Returns120x120()
+    {
+        var (w, h) = ImageToAsciiService.GetDimensions("l");
+        Assert.Equal(120, w);
+        Assert.Equal(120, h);
+    }
+
+    [Fact]
+    public void GetDimensions_Default_Returns80x80()
+    {
+        var (w, h) = ImageToAsciiService.GetDimensions("m");
+        Assert.Equal(HubConstants.AsciiArtWidth, w);
+        Assert.Equal(HubConstants.AsciiArtHeightHalfBlock, h);
+    }
+
+    [Fact]
+    public void GetDimensions_Null_ReturnsDefault()
+    {
+        var (w, h) = ImageToAsciiService.GetDimensions(null);
+        Assert.Equal(HubConstants.AsciiArtWidth, w);
+        Assert.Equal(HubConstants.AsciiArtHeightHalfBlock, h);
+    }
+
+    [Fact]
+    public void GetDimensions_CaseInsensitive()
+    {
+        var (w1, h1) = ImageToAsciiService.GetDimensions("S");
+        var (w2, h2) = ImageToAsciiService.GetDimensions("s");
+        Assert.Equal(w1, w2);
+        Assert.Equal(h1, h2);
+
+        var (w3, h3) = ImageToAsciiService.GetDimensions("L");
+        var (w4, h4) = ImageToAsciiService.GetDimensions("l");
+        Assert.Equal(w3, w4);
+        Assert.Equal(h3, h4);
+    }
+
+    [Fact]
+    public void GetDimensions_UnknownSize_ReturnsDefault()
+    {
+        var (w, h) = ImageToAsciiService.GetDimensions("xl");
+        Assert.Equal(HubConstants.AsciiArtWidth, w);
+        Assert.Equal(HubConstants.AsciiArtHeightHalfBlock, h);
+    }
+}
diff --git a/src/EchoHub.Tests/IrcMessageFormatterTests.cs b/src/EchoHub.Tests/IrcMessageFormatterTests.cs
new file mode 100644
index 0000000..5e407b5
--- /dev/null
+++ b/src/EchoHub.Tests/IrcMessageFormatterTests.cs
@@ -0,0 +1,186 @@
+using EchoHub.Core.DTOs;
+using EchoHub.Core.Models;
+using EchoHub.Server.Irc;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class IrcMessageFormatterTests
+{
+    private static MessageDto CreateMessage(
+        MessageType type = MessageType.Text,
+        string content = "hello",
+        string sender = "alice",
+        string channel = "general",
+        string? attachmentUrl = null,
+        string? attachmentFileName = null,
+        List<EmbedDto>? embeds = null) => new(
+        Id: Guid.NewGuid(),
+        Content: content,
+        SenderUsername: sender,
+        SenderNicknameColor: null,
+        ChannelName: channel,
+        Type: type,
+        AttachmentUrl: attachmentUrl,
+        AttachmentFileName: attachmentFileName,
+        SentAt: DateTimeOffset.UtcNow,
+        Embeds: embeds);
+
+    // ── FormatMessage ─────────────────────────────────────────────────
+
+    [Fact]
+    public void FormatMessage_TextMessage_FormatsAsPRIVMSG()
+    {
+        var msg = CreateMessage(content: "Hello world");
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.Single(lines);
+        Assert.Contains("PRIVMSG #general :Hello world", lines[0]);
+        Assert.StartsWith(":alice!alice@echohub", lines[0]);
+    }
+
+    [Fact]
+    public void FormatMessage_TextMessage_WithEmbeds_AppendsEmbedLines()
+    {
+        var embeds = new List<EmbedDto>
+        {
+            new("GitHub", "Repo Title", "A description", null, "https://github.com/test")
+        };
+        var msg = CreateMessage(content: "check this out https://github.com/test", embeds: embeds);
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.True(lines.Count >= 2);
+        Assert.Contains("PRIVMSG #general :check this out", lines[0]);
+        // Embed lines contain the Unicode pipe char and site/title
+        Assert.Contains("GitHub", lines[1]);
+        Assert.Contains("Repo Title", lines[1]);
+    }
+
+    [Fact]
+    public void FormatMessage_ImageMessage_IncludesImageTagAndDownloadUrl()
+    {
+        var msg = CreateMessage(
+            type: MessageType.Image,
+            content: "{F:FF0000}\u2588{X}",
+            attachmentUrl: "/api/files/abc",
+            attachmentFileName: "photo.png");
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.True(lines.Count >= 2);
+        Assert.Contains("[Image: photo.png]", lines[0]);
+        Assert.Contains("Download: /api/files/abc", lines[1]);
+    }
+
+    [Fact]
+    public void FormatMessage_FileMessage_IncludesFileTag()
+    {
+        var msg = CreateMessage(
+            type: MessageType.File,
+            content: "report.pdf",
+            attachmentUrl: "/api/files/xyz",
+            attachmentFileName: "report.pdf");
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.Single(lines);
+        Assert.Contains("[File: report.pdf]", lines[0]);
+        Assert.Contains("/api/files/xyz", lines[0]);
+    }
+
+    [Fact]
+    public void FormatMessage_AudioMessage_IncludesMusicNoteAndAudioTag()
+    {
+        var msg = CreateMessage(
+            type: MessageType.Audio,
+            content: "song.mp3",
+            attachmentUrl: "/api/files/def",
+            attachmentFileName: "song.mp3");
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.Single(lines);
+        Assert.Contains("\u266a", lines[0]); // ♪
+        Assert.Contains("[Audio: song.mp3]", lines[0]);
+        Assert.Contains("/api/files/def", lines[0]);
+    }
+
+    // ── ColorTagsToAnsi ───────────────────────────────────────────────
+
+    [Fact]
+    public void ColorTagsToAnsi_ForegroundTag_ConvertsToAnsiEscape()
+    {
+        var result = IrcMessageFormatter.ColorTagsToAnsi("{F:FF0000}text");
+        Assert.Contains("\x1b[38;2;255;0;0m", result);
+        Assert.Contains("text", result);
+    }
+
+    [Fact]
+    public void ColorTagsToAnsi_BackgroundTag_ConvertsToAnsiEscape()
+    {
+        var result = IrcMessageFormatter.ColorTagsToAnsi("{B:00FF00}text");
+        Assert.Contains("\x1b[48;2;0;255;0m", result);
+    }
+
+    [Fact]
+    public void ColorTagsToAnsi_ResetTag_ConvertsToAnsiReset()
+    {
+        var result = IrcMessageFormatter.ColorTagsToAnsi("{X}");
+        Assert.Equal("\x1b[0m", result);
+    }
+
+    [Fact]
+    public void ColorTagsToAnsi_NoTags_ReturnsUnchanged()
+    {
+        var result = IrcMessageFormatter.ColorTagsToAnsi("plain text");
+        Assert.Equal("plain text", result);
+    }
+
+    [Fact]
+    public void ColorTagsToAnsi_MultipleTags_ConvertsAll()
+    {
+        var result = IrcMessageFormatter.ColorTagsToAnsi("{F:FF0000}red{F:0000FF}blue{X}");
+        Assert.Contains("\x1b[38;2;255;0;0m", result);
+        Assert.Contains("\x1b[38;2;0;0;255m", result);
+        Assert.Contains("\x1b[0m", result);
+        Assert.Contains("red", result);
+        Assert.Contains("blue", result);
+    }
+
+    // ── SplitMessage ──────────────────────────────────────────────────
+
+    [Fact]
+    public void SplitMessage_ShortMessage_ReturnsSingleChunk()
+    {
+        var result = IrcMessageFormatter.SplitMessage("Hello", 400);
+        Assert.Single(result);
+        Assert.Equal("Hello", result[0]);
+    }
+
+    [Fact]
+    public void SplitMessage_LongMessage_SplitsAtWordBoundary()
+    {
+        var words = string.Join(" ", Enumerable.Repeat("word", 200));
+        var result = IrcMessageFormatter.SplitMessage(words, 50);
+
+        Assert.True(result.Count > 1);
+        foreach (var chunk in result)
+            Assert.True(System.Text.Encoding.UTF8.GetByteCount(chunk) <= 50);
+    }
+
+    [Fact]
+    public void SplitMessage_EmptyMessage_ReturnsSingleEmptyChunk()
+    {
+        var result = IrcMessageFormatter.SplitMessage("", 400);
+        Assert.Single(result);
+        Assert.Equal("", result[0]);
+    }
+
+    [Fact]
+    public void SplitMessage_SingleLongWord_KeptAsOneChunk()
+    {
+        var longWord = new string('a', 500);
+        var result = IrcMessageFormatter.SplitMessage(longWord, 400);
+
+        // Single word can't be split at word boundary, so it stays as one chunk
+        Assert.Single(result);
+        Assert.Equal(longWord, result[0]);
+    }
+}
diff --git a/src/EchoHub.Tests/JwtTokenServiceTests.cs b/src/EchoHub.Tests/JwtTokenServiceTests.cs
new file mode 100644
index 0000000..a9367c8
--- /dev/null
+++ b/src/EchoHub.Tests/JwtTokenServiceTests.cs
@@ -0,0 +1,195 @@
+using System.IdentityModel.Tokens.Jwt;
+using EchoHub.Core.Models;
+using EchoHub.Server.Auth;
+using Microsoft.Extensions.Configuration;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class JwtTokenServiceTests
+{
+    private const string TestSecret = "this_is_a_test_secret_key_that_is_long_enough_for_hmac_sha256";
+    private const string TestIssuer = "TestIssuer";
+    private const string TestAudience = "TestAudience";
+
+    private static JwtTokenService CreateService(
+        string? secret = null, string? issuer = null, string? audience = null)
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["Jwt:Secret"] = secret ?? TestSecret,
+                ["Jwt:Issuer"] = issuer ?? TestIssuer,
+                ["Jwt:Audience"] = audience ?? TestAudience,
+            })
+            .Build();
+
+        return new JwtTokenService(config);
+    }
+
+    private static User CreateUser(
+        string username = "alice",
+        ServerRole role = ServerRole.Member,
+        string? displayName = null) => new()
+        {
+            Id = Guid.NewGuid(),
+            Username = username,
+            PasswordHash = "hash",
+            DisplayName = displayName,
+            Role = role,
+        };
+
+    // ── Constructor ───────────────────────────────────────────────────
+
+    [Fact]
+    public void Constructor_MissingSecret_Throws()
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["Jwt:Issuer"] = TestIssuer,
+                ["Jwt:Audience"] = TestAudience,
+            })
+            .Build();
+
+        Assert.Throws<InvalidOperationException>(() => new JwtTokenService(config));
+    }
+
+    [Fact]
+    public void Constructor_MissingIssuer_Throws()
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["Jwt:Secret"] = TestSecret,
+                ["Jwt:Audience"] = TestAudience,
+            })
+            .Build();
+
+        Assert.Throws<InvalidOperationException>(() => new JwtTokenService(config));
+    }
+
+    [Fact]
+    public void Constructor_MissingAudience_Throws()
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["Jwt:Secret"] = TestSecret,
+                ["Jwt:Issuer"] = TestIssuer,
+            })
+            .Build();
+
+        Assert.Throws<InvalidOperationException>(() => new JwtTokenService(config));
+    }
+
+    // ── GenerateAccessToken ───────────────────────────────────────────
+
+    [Fact]
+    public void GenerateAccessToken_ContainsExpectedClaims()
+    {
+        var service = CreateService();
+        var user = CreateUser(username: "bob", role: ServerRole.Admin, displayName: "Bob Smith");
+
+        var (token, _) = service.GenerateAccessToken(user);
+        var handler = new JwtSecurityTokenHandler();
+        var jwt = handler.ReadJwtToken(token);
+
+        Assert.Equal(user.Id.ToString(), jwt.Claims.First(c => c.Type == "sub").Value);
+        Assert.Equal("bob", jwt.Claims.First(c => c.Type == "username").Value);
+        Assert.Equal("Bob Smith", jwt.Claims.First(c => c.Type == "display_name").Value);
+        Assert.Equal("Admin", jwt.Claims.First(c => c.Type == "role").Value);
+        Assert.NotNull(jwt.Claims.FirstOrDefault(c => c.Type == "jti"));
+    }
+
+    [Fact]
+    public void GenerateAccessToken_ExpiresIn15Minutes()
+    {
+        var service = CreateService();
+        var user = CreateUser();
+
+        var (_, expiresAt) = service.GenerateAccessToken(user);
+        var diff = expiresAt - DateTimeOffset.UtcNow;
+
+        // Should be approximately 15 minutes (allow 30s tolerance)
+        Assert.InRange(diff.TotalMinutes, 14.5, 15.5);
+    }
+
+    [Fact]
+    public void GenerateAccessToken_DifferentTokensForSameUser()
+    {
+        var service = CreateService();
+        var user = CreateUser();
+
+        var (token1, _) = service.GenerateAccessToken(user);
+        var (token2, _) = service.GenerateAccessToken(user);
+
+        Assert.NotEqual(token1, token2);
+    }
+
+    [Fact]
+    public void GenerateAccessToken_DisplayNameFallsBackToUsername()
+    {
+        var service = CreateService();
+        var user = CreateUser(username: "alice"); // DisplayName is null
+
+        var (token, _) = service.GenerateAccessToken(user);
+        var handler = new JwtSecurityTokenHandler();
+        var jwt = handler.ReadJwtToken(token);
+
+        Assert.Equal("alice", jwt.Claims.First(c => c.Type == "display_name").Value);
+    }
+
+    // ── GenerateRefreshToken ──────────────────────────────────────────
+
+    [Fact]
+    public void GenerateRefreshToken_Returns88CharBase64()
+    {
+        var token = JwtTokenService.GenerateRefreshToken();
+
+        // 64 bytes → 88 base64 characters
+        Assert.Equal(88, token.Length);
+        // Should be valid base64
+        var bytes = Convert.FromBase64String(token);
+        Assert.Equal(64, bytes.Length);
+    }
+
+    [Fact]
+    public void GenerateRefreshToken_UniqueBetweenCalls()
+    {
+        var token1 = JwtTokenService.GenerateRefreshToken();
+        var token2 = JwtTokenService.GenerateRefreshToken();
+
+        Assert.NotEqual(token1, token2);
+    }
+
+    // ── HashToken ─────────────────────────────────────────────────────
+
+    [Fact]
+    public void HashToken_DeterministicForSameInput()
+    {
+        var hash1 = JwtTokenService.HashToken("test-token");
+        var hash2 = JwtTokenService.HashToken("test-token");
+
+        Assert.Equal(hash1, hash2);
+    }
+
+    [Fact]
+    public void HashToken_DifferentForDifferentInput()
+    {
+        var hash1 = JwtTokenService.HashToken("token-a");
+        var hash2 = JwtTokenService.HashToken("token-b");
+
+        Assert.NotEqual(hash1, hash2);
+    }
+
+    [Fact]
+    public void HashToken_ReturnsBase64String()
+    {
+        var hash = JwtTokenService.HashToken("test-token");
+
+        // SHA256 → 32 bytes → 44 base64 characters
+        var bytes = Convert.FromBase64String(hash);
+        Assert.Equal(32, bytes.Length);
+    }
+}
diff --git a/src/EchoHub.Tests/LinkEmbedServiceTests.cs b/src/EchoHub.Tests/LinkEmbedServiceTests.cs
new file mode 100644
index 0000000..735d67a
--- /dev/null
+++ b/src/EchoHub.Tests/LinkEmbedServiceTests.cs
@@ -0,0 +1,192 @@
+using System.Reflection;
+using EchoHub.Server.Services;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class LinkEmbedServiceTests
+{
+    private static readonly MethodInfo ExtractUrlsMethod = typeof(LinkEmbedService)
+        .GetMethod("ExtractUrls", BindingFlags.NonPublic | BindingFlags.Static)!;
+
+    private static readonly MethodInfo IsPrivateHostMethod = typeof(LinkEmbedService)
+        .GetMethod("IsPrivateHost", BindingFlags.NonPublic | BindingFlags.Static)!;
+
+    private static readonly MethodInfo ParseOgTagsMethod = typeof(LinkEmbedService)
+        .GetMethod("ParseOgTags", BindingFlags.NonPublic | BindingFlags.Static)!;
+
+    private static List<string> ExtractUrls(string content) =>
+        (List<string>)ExtractUrlsMethod.Invoke(null, [content])!;
+
+    private static bool IsPrivateHost(Uri uri) =>
+        (bool)IsPrivateHostMethod.Invoke(null, [uri])!;
+
+    private static Dictionary<string, string> ParseOgTags(string html) =>
+        (Dictionary<string, string>)ParseOgTagsMethod.Invoke(null, [html])!;
+
+    // ── ExtractUrls ───────────────────────────────────────────────────
+
+    [Fact]
+    public void ExtractUrls_SingleUrl_ReturnsIt()
+    {
+        var urls = ExtractUrls("Check this: https://example.com");
+        Assert.Single(urls);
+        Assert.Equal("https://example.com", urls[0]);
+    }
+
+    [Fact]
+    public void ExtractUrls_MultipleUrls_ReturnsAll()
+    {
+        var urls = ExtractUrls("See https://a.com and https://b.com");
+        Assert.Equal(2, urls.Count);
+        Assert.Contains("https://a.com", urls);
+        Assert.Contains("https://b.com", urls);
+    }
+
+    [Fact]
+    public void ExtractUrls_UrlWithTrailingPunctuation_Trimmed()
+    {
+        var urls = ExtractUrls("Visit https://example.com.");
+        Assert.Single(urls);
+        Assert.Equal("https://example.com", urls[0]);
+    }
+
+    [Fact]
+    public void ExtractUrls_NoUrls_ReturnsEmpty()
+    {
+        var urls = ExtractUrls("No links here");
+        Assert.Empty(urls);
+    }
+
+    [Fact]
+    public void ExtractUrls_MaxUrlsLimit_Respected()
+    {
+        // EmbedMaxUrlsPerMessage = 3
+        var text = "https://a.com https://b.com https://c.com https://d.com https://e.com";
+        var urls = ExtractUrls(text);
+        Assert.Equal(3, urls.Count);
+    }
+
+    [Fact]
+    public void ExtractUrls_DuplicateUrls_Deduped()
+    {
+        var urls = ExtractUrls("https://example.com and https://example.com again");
+        Assert.Single(urls);
+    }
+
+    [Fact]
+    public void ExtractUrls_HttpUrl_Extracted()
+    {
+        var urls = ExtractUrls("http://example.com");
+        Assert.Single(urls);
+        Assert.StartsWith("http://", urls[0]);
+    }
+
+    // ── IsPrivateHost ─────────────────────────────────────────────────
+
+    [Fact]
+    public void IsPrivateHost_Localhost_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://localhost/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_LoopbackIP_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://127.0.0.1/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_10Network_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://10.0.0.1/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_172_16Network_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://172.16.0.1/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_192_168Network_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://192.168.1.1/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_PublicIP_ReturnsFalse()
+    {
+        Assert.False(IsPrivateHost(new Uri("http://8.8.8.8/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_PublicDomain_ReturnsFalse()
+    {
+        Assert.False(IsPrivateHost(new Uri("https://example.com/test")));
+    }
+
+    [Fact]
+    public void IsPrivateHost_ZeroIP_ReturnsTrue()
+    {
+        Assert.True(IsPrivateHost(new Uri("http://0.0.0.0/test")));
+    }
+
+    // ── ParseOgTags ───────────────────────────────────────────────────
+
+    [Fact]
+    public void ParseOgTags_StandardOgTags_ParsedCorrectly()
+    {
+        var html = """
+            <html><head>
+            <meta property="og:title" content="Test Title" />
+            <meta property="og:description" content="A description" />
+            <meta property="og:site_name" content="TestSite" />
+            </head></html>
+            """;
+        var tags = ParseOgTags(html);
+
+        Assert.Equal("Test Title", tags["title"]);
+        Assert.Equal("A description", tags["description"]);
+        Assert.Equal("TestSite", tags["site_name"]);
+    }
+
+    [Fact]
+    public void ParseOgTags_ReversedOrder_ParsedCorrectly()
+    {
+        var html = """<meta content="Reversed Title" property="og:title" />""";
+        var tags = ParseOgTags(html);
+
+        Assert.Equal("Reversed Title", tags["title"]);
+    }
+
+    [Fact]
+    public void ParseOgTags_NoOgTags_ReturnsEmptyDictionary()
+    {
+        var html = "<html><head><title>Page</title></head></html>";
+        var tags = ParseOgTags(html);
+
+        Assert.Empty(tags);
+    }
+
+    [Fact]
+    public void ParseOgTags_SingleQuotes_ParsedCorrectly()
+    {
+        var html = """<meta property='og:title' content='Single Quoted' />""";
+        var tags = ParseOgTags(html);
+
+        Assert.Equal("Single Quoted", tags["title"]);
+    }
+
+    [Fact]
+    public void ParseOgTags_DuplicateKeys_FirstWins()
+    {
+        var html = """
+            <meta property="og:title" content="First" />
+            <meta property="og:title" content="Second" />
+            """;
+        var tags = ParseOgTags(html);
+
+        Assert.Equal("First", tags["title"]);
+    }
+}