diff --git a/src/AcDream.Core.Net/Messages/SocialActions.cs b/src/AcDream.Core.Net/Messages/SocialActions.cs
new file mode 100644
index 0000000..86f7524
--- /dev/null
+++ b/src/AcDream.Core.Net/Messages/SocialActions.cs
@@ -0,0 +1,174 @@
+using System;
+using System.Buffers.Binary;
+using System.Text;
+
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Outbound social + query GameActions. These share a common pattern:
+/// single-target / single-parameter GameActions inside the <c>0xF7B1</c>
+/// envelope.
+///
+/// <para>
+/// Wire format:
+/// <code>
+///   u32 0xF7B1                    envelope
+///   u32 gameActionSequence
+///   u32 subOpcode
+///   &lt;payload&gt;                   per-action
+/// </code>
+/// </para>
+///
+/// <para>
+/// References: r08 §3 rows for each opcode.
+/// </para>
+/// </summary>
+public static class SocialActions
+{
+    public const uint GameActionEnvelope = 0xF7B1u;
+
+    // Queries
+    public const uint QueryHealthOpcode         = 0x01BFu; // u32 targetGuid
+    public const uint PingRequestOpcode         = 0x01E9u; // u32 clientId
+
+    // Fellowship
+    public const uint FellowshipCreateOpcode    = 0x00A2u; // string16L name, bool openness, bool shareXP
+    public const uint FellowshipQuitOpcode      = 0x00A3u; // bool disband
+    public const uint FellowshipDismissOpcode   = 0x00A4u; // u32 guid
+    public const uint FellowshipRecruitOpcode   = 0x00A5u; // u32 guid
+    public const uint FellowshipUpdateOpcode    = 0x00A6u; // bool open
+
+    // Character options
+    public const uint SetCharacterOptionsOpcode = 0x01A1u; // u32 options bitmap
+
+    // Chat channels
+    public const uint AddChannelOpcode    = 0x0145u; // string16L channelName
+    public const uint RemoveChannelOpcode = 0x0146u; // string16L channelName
+
+    /// <summary>Query a target's health — server replies with UpdateHealth (0x01C0).</summary>
+    public static byte[] BuildQueryHealth(uint seq, uint targetGuid)
+    {
+        byte[] body = new byte[16];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  QueryHealthOpcode);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), targetGuid);
+        return body;
+    }
+
+    /// <summary>Keepalive ping — server echoes with PingResponse (0x01EA).</summary>
+    public static byte[] BuildPingRequest(uint seq, uint clientId)
+    {
+        byte[] body = new byte[16];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  PingRequestOpcode);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), clientId);
+        return body;
+    }
+
+    /// <summary>Create a fellowship with a chosen name + options.</summary>
+    public static byte[] BuildFellowshipCreate(
+        uint seq, string fellowshipName, bool openness, bool shareXp)
+    {
+        byte[] name = PackString16L(fellowshipName);
+        // 2 bools consume 2 bytes + alignment pad to 4.
+        int boolBlock = 2;
+        int pad = (4 - ((name.Length + boolBlock) & 3)) & 3;
+        byte[] body = new byte[12 + name.Length + boolBlock + pad];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipCreateOpcode);
+        Array.Copy(name, 0, body, 12, name.Length);
+        body[12 + name.Length] = openness ? (byte)1 : (byte)0;
+        body[12 + name.Length + 1] = shareXp ? (byte)1 : (byte)0;
+        return body;
+    }
+
+    /// <summary>Quit your current fellowship (optionally disband if leader).</summary>
+    public static byte[] BuildFellowshipQuit(uint seq, bool disband)
+    {
+        byte[] body = new byte[16]; // envelope + 1 byte bool aligned to 4
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipQuitOpcode);
+        body[12] = disband ? (byte)1 : (byte)0;
+        return body;
+    }
+
+    /// <summary>Dismiss a specific vassal from your fellowship.</summary>
+    public static byte[] BuildFellowshipDismiss(uint seq, uint targetGuid)
+        => SingleGuid(seq, FellowshipDismissOpcode, targetGuid);
+
+    /// <summary>Recruit a target into your fellowship.</summary>
+    public static byte[] BuildFellowshipRecruit(uint seq, uint targetGuid)
+        => SingleGuid(seq, FellowshipRecruitOpcode, targetGuid);
+
+    /// <summary>Toggle fellowship open / closed recruiting.</summary>
+    public static byte[] BuildFellowshipUpdate(uint seq, bool open)
+    {
+        byte[] body = new byte[16];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipUpdateOpcode);
+        body[12] = open ? (byte)1 : (byte)0;
+        return body;
+    }
+
+    /// <summary>Push the client's character-options bitmap to the server.</summary>
+    public static byte[] BuildSetCharacterOptions(uint seq, uint optionsBitmap)
+    {
+        byte[] body = new byte[16];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  SetCharacterOptionsOpcode);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), optionsBitmap);
+        return body;
+    }
+
+    /// <summary>Subscribe to a named chat channel.</summary>
+    public static byte[] BuildAddChannel(uint seq, string channelName)
+        => SingleString(seq, AddChannelOpcode, channelName);
+
+    /// <summary>Unsubscribe from a named chat channel.</summary>
+    public static byte[] BuildRemoveChannel(uint seq, string channelName)
+        => SingleString(seq, RemoveChannelOpcode, channelName);
+
+    // ── Helpers ──────────────────────────────────────────────────────────────
+
+    private static byte[] SingleGuid(uint seq, uint sub, uint guid)
+    {
+        byte[] body = new byte[16];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  sub);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), guid);
+        return body;
+    }
+
+    private static byte[] SingleString(uint seq, uint sub, string s)
+    {
+        byte[] str = PackString16L(s);
+        byte[] body = new byte[12 + str.Length];
+        BinaryPrimitives.WriteUInt32LittleEndian(body,           GameActionEnvelope);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4), seq);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8), sub);
+        Array.Copy(str, 0, body, 12, str.Length);
+        return body;
+    }
+
+    private static byte[] PackString16L(string s)
+    {
+        ArgumentNullException.ThrowIfNull(s);
+        byte[] data = Encoding.ASCII.GetBytes(s);
+        if (data.Length > ushort.MaxValue)
+            throw new ArgumentException("String too long for 16-bit length prefix.", nameof(s));
+
+        int recordSize = 2 + data.Length;
+        int padding = (4 - (recordSize & 3)) & 3;
+        byte[] result = new byte[recordSize + padding];
+        BinaryPrimitives.WriteUInt16LittleEndian(result, (ushort)data.Length);
+        Array.Copy(data, 0, result, 2, data.Length);
+        return result;
+    }
+}
diff --git a/tests/AcDream.Core.Net.Tests/Messages/SocialActionsTests.cs b/tests/AcDream.Core.Net.Tests/Messages/SocialActionsTests.cs
new file mode 100644
index 0000000..3018ae1
--- /dev/null
+++ b/tests/AcDream.Core.Net.Tests/Messages/SocialActionsTests.cs
@@ -0,0 +1,111 @@
+using System;
+using System.Buffers.Binary;
+using System.Text;
+using AcDream.Core.Net.Messages;
+using Xunit;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+public sealed class SocialActionsTests
+{
+    [Fact]
+    public void BuildQueryHealth_HasOpcode0x01BFAndGuid()
+    {
+        byte[] body = SocialActions.BuildQueryHealth(seq: 3, targetGuid: 0xCAFE);
+        Assert.Equal(SocialActions.QueryHealthOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(0xCAFEu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildPingRequest_HasOpcode0x01E9()
+    {
+        byte[] body = SocialActions.BuildPingRequest(seq: 1, clientId: 42);
+        Assert.Equal(SocialActions.PingRequestOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(42u,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildFellowshipCreate_StringThenBools()
+    {
+        byte[] body = SocialActions.BuildFellowshipCreate(
+            seq: 1, fellowshipName: "Team", openness: true, shareXp: false);
+
+        Assert.Equal(SocialActions.FellowshipCreateOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        // String at offset 12: u16 length = 4
+        ushort len = BinaryPrimitives.ReadUInt16LittleEndian(body.AsSpan(12));
+        Assert.Equal(4, len);
+        Assert.Equal("Team", Encoding.ASCII.GetString(body.AsSpan(14, 4)));
+        // string16L record = 2+4=6, pad 2 → advance by 8.
+        // Then 2 bools at offset 20,21.
+        Assert.Equal(1, body[20]);  // openness true
+        Assert.Equal(0, body[21]);  // shareXp false
+    }
+
+    [Fact]
+    public void BuildFellowshipQuit_CarriesDisbandFlag()
+    {
+        byte[] body = SocialActions.BuildFellowshipQuit(seq: 1, disband: true);
+        Assert.Equal(SocialActions.FellowshipQuitOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(1, body[12]);
+    }
+
+    [Fact]
+    public void BuildFellowshipDismiss_HasGuid()
+    {
+        byte[] body = SocialActions.BuildFellowshipDismiss(seq: 1, targetGuid: 0xDEAD);
+        Assert.Equal(SocialActions.FellowshipDismissOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(0xDEADu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildFellowshipRecruit_HasGuid()
+    {
+        byte[] body = SocialActions.BuildFellowshipRecruit(seq: 1, targetGuid: 0xBEEF);
+        Assert.Equal(SocialActions.FellowshipRecruitOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+    }
+
+    [Fact]
+    public void BuildFellowshipUpdate_HasOpenBool()
+    {
+        byte[] body = SocialActions.BuildFellowshipUpdate(seq: 1, open: true);
+        Assert.Equal(SocialActions.FellowshipUpdateOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(1, body[12]);
+    }
+
+    [Fact]
+    public void BuildSetCharacterOptions_HasBitmap()
+    {
+        byte[] body = SocialActions.BuildSetCharacterOptions(seq: 1, optionsBitmap: 0xDEADBEEFu);
+        Assert.Equal(0xDEADBEEFu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildAddChannel_ContainsName()
+    {
+        byte[] body = SocialActions.BuildAddChannel(seq: 1, channelName: "Trade");
+        Assert.Equal(SocialActions.AddChannelOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        ushort len = BinaryPrimitives.ReadUInt16LittleEndian(body.AsSpan(12));
+        Assert.Equal(5, len);
+        Assert.Equal("Trade", Encoding.ASCII.GetString(body.AsSpan(14, 5)));
+    }
+
+    [Fact]
+    public void BuildRemoveChannel_HasOpcode0x0146()
+    {
+        byte[] body = SocialActions.BuildRemoveChannel(seq: 1, channelName: "General");
+        Assert.Equal(SocialActions.RemoveChannelOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+    }
+}