diff --git a/protocol/build.gradle.kts b/protocol/build.gradle.kts
new file mode 100644
index 00000000..f4911c10
--- /dev/null
+++ b/protocol/build.gradle.kts
@@ -0,0 +1,28 @@
+plugins {
+    `maven-publish`
+    kotlin("jvm")
+}
+
+dependencies {
+    api("io.netty:netty-codec:${Versions.netty}")
+
+    implementation(project(":buffer"))
+
+    testImplementation(project(":buffer"))
+}
+
+publishing {
+    publications.create<MavenPublication>("maven") {
+        from(components["java"])
+
+        pom {
+            packaging = "jar"
+            name.set("OpenRS2 Protocol")
+            description.set(
+                """
+                An implementation of the RuneScape protocol.
+            """.trimIndent()
+            )
+        }
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Request.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Request.kt
new file mode 100644
index 00000000..99ac827e
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Request.kt
@@ -0,0 +1,15 @@
+package org.openrs2.protocol.js5
+
+public sealed class Js5Request {
+    public data class Group(
+        public val prefetch: Boolean,
+        public val archive: Int,
+        public val group: Int
+    ) : Js5Request()
+
+    public object LoggedIn : Js5Request()
+    public object LoggedOut : Js5Request()
+    public data class Rekey(public val key: Int) : Js5Request()
+    public object Connected : Js5Request()
+    public object Disconnect : Js5Request()
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestDecoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestDecoder.kt
new file mode 100644
index 00000000..13e5bfdb
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestDecoder.kt
@@ -0,0 +1,35 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.ByteToMessageDecoder
+import io.netty.handler.codec.DecoderException
+
+public class Js5RequestDecoder : ByteToMessageDecoder() {
+    override fun decode(ctx: ChannelHandlerContext, input: ByteBuf, out: MutableList<Any>) {
+        if (input.readableBytes() < 4) {
+            return
+        }
+
+        val opcode = input.readUnsignedByte().toInt()
+
+        if (opcode == 0 || opcode == 1) {
+            val archive = input.readUnsignedByte().toInt()
+            val group = input.readUnsignedShort()
+            out += Js5Request.Group(opcode == 0, archive, group)
+        } else if (opcode == 4) {
+            val key = input.readUnsignedByte().toInt()
+            input.skipBytes(2)
+            out += Js5Request.Rekey(key)
+        } else {
+            input.skipBytes(3)
+            out += when (opcode) {
+                2 -> Js5Request.LoggedIn
+                3 -> Js5Request.LoggedOut
+                6 -> Js5Request.Connected
+                7 -> Js5Request.Disconnect
+                else -> throw DecoderException("Unknown JS5 opcode: $opcode")
+            }
+        }
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestEncoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestEncoder.kt
new file mode 100644
index 00000000..71f85e71
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5RequestEncoder.kt
@@ -0,0 +1,44 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandler
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.MessageToByteEncoder
+
+@ChannelHandler.Sharable
+public class Js5RequestEncoder : MessageToByteEncoder<Js5Request>(Js5Request::class.java) {
+    override fun encode(ctx: ChannelHandlerContext, msg: Js5Request, out: ByteBuf) {
+        when (msg) {
+            is Js5Request.Group -> {
+                out.writeByte(if (msg.prefetch) 0 else 1)
+                out.writeByte(msg.archive)
+                out.writeShort(msg.group)
+            }
+            is Js5Request.Rekey -> {
+                out.writeByte(4)
+                out.writeByte(msg.key)
+                out.writeZero(2)
+            }
+            is Js5Request.LoggedIn -> encodeSimple(out, 2)
+            is Js5Request.LoggedOut -> encodeSimple(out, 3)
+            is Js5Request.Connected -> {
+                out.writeByte(6)
+                out.writeMedium(3)
+            }
+            is Js5Request.Disconnect -> encodeSimple(out, 7)
+        }
+    }
+
+    private fun encodeSimple(out: ByteBuf, opcode: Int) {
+        out.writeByte(opcode)
+        out.writeZero(3)
+    }
+
+    override fun allocateBuffer(ctx: ChannelHandlerContext, msg: Js5Request, preferDirect: Boolean): ByteBuf {
+        return if (preferDirect) {
+            ctx.alloc().ioBuffer(4, 4)
+        } else {
+            ctx.alloc().heapBuffer(4, 4)
+        }
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Response.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Response.kt
new file mode 100644
index 00000000..a536cec6
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5Response.kt
@@ -0,0 +1,43 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.util.ReferenceCounted
+
+public data class Js5Response(
+    public val prefetch: Boolean,
+    public val archive: Int,
+    public val group: Int,
+    public val data: ByteBuf
+) : ReferenceCounted {
+    override fun refCnt(): Int {
+        return data.refCnt()
+    }
+
+    override fun retain(): Js5Response {
+        data.retain()
+        return this
+    }
+
+    override fun retain(increment: Int): Js5Response {
+        data.retain(increment)
+        return this
+    }
+
+    override fun touch(): Js5Response {
+        data.touch()
+        return this
+    }
+
+    override fun touch(hint: Any?): Js5Response {
+        data.touch(hint)
+        return this
+    }
+
+    override fun release(): Boolean {
+        return data.release()
+    }
+
+    override fun release(decrement: Int): Boolean {
+        return data.release(decrement)
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoder.kt
new file mode 100644
index 00000000..5e4fe156
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoder.kt
@@ -0,0 +1,97 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.Unpooled
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.ByteToMessageDecoder
+import io.netty.handler.codec.DecoderException
+import kotlin.math.min
+
+public class Js5ResponseDecoder : ByteToMessageDecoder() {
+    private enum class State {
+        READ_HEADER,
+        READ_DATA
+    }
+
+    private var state = State.READ_HEADER
+    private var prefetch: Boolean = false
+    private var archive: Int = 0
+    private var group: Int = 0
+    private var type: Int = 0
+    private var data: ByteBuf = Unpooled.EMPTY_BUFFER
+
+    override fun decode(ctx: ChannelHandlerContext, input: ByteBuf, out: MutableList<Any>) {
+        if (state == State.READ_HEADER) {
+            if (input.readableBytes() < 8) {
+                return
+            }
+
+            archive = input.readUnsignedByte().toInt()
+            group = input.readUnsignedShort()
+            type = input.readUnsignedByte().toInt()
+
+            if (type and 0x80 != 0) {
+                prefetch = true
+                type = type and 0x80.inv()
+            } else {
+                prefetch = false
+            }
+
+            val len = input.readInt()
+            if (len < 0) {
+                throw DecoderException("Length is negative: $len")
+            }
+
+            val totalLen = if (type == 0) {
+                len + 5
+            } else {
+                len + 9
+            }
+
+            if (totalLen < 0) {
+                throw DecoderException("Total length exceeds maximum ByteBuf size")
+            }
+
+            // TODO(gpe): release data here?
+            data = ctx.alloc().buffer(totalLen, totalLen)
+            data.writeByte(type)
+            data.writeInt(len)
+
+            state = State.READ_DATA
+        }
+
+        if (state == State.READ_DATA) {
+            while (data.isWritable) {
+                val blockLen = min(511 - ((data.readableBytes() + 3) % 511), data.writableBytes())
+                val last = data.writableBytes() <= blockLen
+
+                val blockLenIncludingTrailer = if (last) {
+                    blockLen
+                } else {
+                    blockLen + 1
+                }
+
+                if (input.readableBytes() < blockLenIncludingTrailer) {
+                    return
+                }
+
+                data.writeBytes(input, blockLen)
+
+                if (!last && input.readUnsignedByte().toInt() != 0xFF) {
+                    throw DecoderException("Invalid block trailer")
+                }
+            }
+
+            out += Js5Response(prefetch, archive, group, data)
+
+            data = Unpooled.EMPTY_BUFFER
+
+            state = State.READ_HEADER
+        }
+    }
+
+    override fun handlerRemoved0(ctx: ChannelHandlerContext?) {
+        data.release()
+        data = Unpooled.EMPTY_BUFFER
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoder.kt
new file mode 100644
index 00000000..ccd6882e
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoder.kt
@@ -0,0 +1,45 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandler
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.EncoderException
+import io.netty.handler.codec.MessageToByteEncoder
+import kotlin.math.min
+
+@ChannelHandler.Sharable
+public class Js5ResponseEncoder : MessageToByteEncoder<Js5Response>(Js5Response::class.java) {
+    override fun encode(ctx: ChannelHandlerContext, msg: Js5Response, out: ByteBuf) {
+        out.writeByte(msg.archive)
+        out.writeShort(msg.group)
+
+        if (!msg.data.isReadable) {
+            // TOOD(gpe): check if the entire container is well-formed?
+            throw EncoderException("Missing compression byte")
+        }
+
+        var compression = msg.data.readUnsignedByte().toInt()
+        if (msg.prefetch) {
+            compression = compression xor 0x80
+        }
+        out.writeByte(compression)
+
+        out.writeBytes(msg.data, min(msg.data.readableBytes(), 507))
+
+        while (msg.data.isReadable) {
+            out.writeByte(0xFF)
+            out.writeBytes(msg.data, min(msg.data.readableBytes(), 511))
+        }
+    }
+
+    override fun allocateBuffer(ctx: ChannelHandlerContext, msg: Js5Response, preferDirect: Boolean): ByteBuf {
+        val dataLen = msg.data.readableBytes()
+        val len = 3 + dataLen + (3 + dataLen) / 511
+
+        return if (preferDirect) {
+            ctx.alloc().ioBuffer(len, len)
+        } else {
+            ctx.alloc().heapBuffer(len, len)
+        }
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorDecoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorDecoder.kt
new file mode 100644
index 00000000..7a9a4584
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorDecoder.kt
@@ -0,0 +1,13 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.MessageToMessageDecoder
+
+public class XorDecoder : MessageToMessageDecoder<ByteBuf>(ByteBuf::class.java) {
+    public var key: Int = 0
+
+    override fun decode(ctx: ChannelHandlerContext, msg: ByteBuf, out: MutableList<Any>) {
+        out += msg.xor(key)
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorEncoder.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorEncoder.kt
new file mode 100644
index 00000000..a67f05f8
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorEncoder.kt
@@ -0,0 +1,13 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.channel.ChannelHandlerContext
+import io.netty.handler.codec.MessageToMessageEncoder
+
+public class XorEncoder : MessageToMessageEncoder<ByteBuf>(ByteBuf::class.java) {
+    public var key: Int = 0
+
+    override fun encode(ctx: ChannelHandlerContext, msg: ByteBuf, out: MutableList<Any>) {
+        out += msg.xor(key)
+    }
+}
diff --git a/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorExtensions.kt b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorExtensions.kt
new file mode 100644
index 00000000..82f561ce
--- /dev/null
+++ b/protocol/src/main/kotlin/org/openrs2/protocol/js5/XorExtensions.kt
@@ -0,0 +1,35 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+
+internal fun ByteBuf.xor(key: Int): ByteBuf {
+    if (key == 0) {
+        return retain()
+    }
+
+    val buf = if (refCnt() == 1) {
+        retain()
+    } else {
+        copy()
+    }
+
+    if (buf.hasArray()) {
+        val array = buf.array()
+
+        val off = buf.arrayOffset() + buf.readerIndex()
+        val len = buf.readableBytes()
+
+        for (i in off until off + len) {
+            array[i] = (array[i].toInt() xor key).toByte()
+        }
+    } else {
+        val off = buf.readerIndex()
+        val len = buf.readableBytes()
+
+        for (i in off until off + len) {
+            buf.setByte(i, buf.getByte(i).toInt() xor key)
+        }
+    }
+
+    return buf
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestDecoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestDecoderTest.kt
new file mode 100644
index 00000000..4cf41107
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestDecoderTest.kt
@@ -0,0 +1,45 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import io.netty.handler.codec.DecoderException
+import org.junit.jupiter.api.assertThrows
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Js5RequestDecoderTest {
+    @Test
+    fun testDecode() {
+        testDecode(byteArrayOf(0, 2, 0, 3), Js5Request.Group(true, 2, 3))
+        testDecode(byteArrayOf(1, 2, 0, 3), Js5Request.Group(false, 2, 3))
+        testDecode(byteArrayOf(4, 0x55, 0, 0), Js5Request.Rekey(0x55))
+        testDecode(byteArrayOf(2, 0, 0, 0), Js5Request.LoggedIn)
+        testDecode(byteArrayOf(3, 0, 0, 0), Js5Request.LoggedOut)
+        testDecode(byteArrayOf(6, 0, 0, 3), Js5Request.Connected)
+        testDecode(byteArrayOf(7, 0, 0, 0), Js5Request.Disconnect)
+    }
+
+    @Test
+    fun testFragmented() {
+        val channel = EmbeddedChannel(Js5RequestDecoder())
+        channel.writeInbound(Unpooled.wrappedBuffer(byteArrayOf(0, 2)))
+        channel.writeInbound(Unpooled.wrappedBuffer(byteArrayOf(0, 3)))
+        assertEquals(Js5Request.Group(true, 2, 3), channel.readInbound())
+    }
+
+    @Test
+    fun testUnknownOpcode() {
+        val channel = EmbeddedChannel(Js5RequestDecoder())
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(Unpooled.wrappedBuffer(byteArrayOf(8, 0, 0, 0)))
+        }
+    }
+
+    private fun testDecode(bytes: ByteArray, expected: Js5Request) {
+        val channel = EmbeddedChannel(Js5RequestDecoder())
+
+        channel.writeInbound(Unpooled.wrappedBuffer(bytes))
+        assertEquals(expected, channel.readInbound())
+    }
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestEncoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestEncoderTest.kt
new file mode 100644
index 00000000..881731c2
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5RequestEncoderTest.kt
@@ -0,0 +1,32 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import org.openrs2.buffer.use
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Js5RequestEncoderTest {
+    @Test
+    fun testEncode() {
+        testEncode(Js5Request.Group(true, 2, 3), byteArrayOf(0, 2, 0, 3))
+        testEncode(Js5Request.Group(false, 2, 3), byteArrayOf(1, 2, 0, 3))
+        testEncode(Js5Request.Rekey(0x55), byteArrayOf(4, 0x55, 0, 0))
+        testEncode(Js5Request.LoggedIn, byteArrayOf(2, 0, 0, 0))
+        testEncode(Js5Request.LoggedOut, byteArrayOf(3, 0, 0, 0))
+        testEncode(Js5Request.Connected, byteArrayOf(6, 0, 0, 3))
+        testEncode(Js5Request.Disconnect, byteArrayOf(7, 0, 0, 0))
+    }
+
+    private fun testEncode(request: Js5Request, expected: ByteArray) {
+        val channel = EmbeddedChannel(Js5RequestEncoder())
+        channel.writeOutbound(request)
+
+        channel.readOutbound<ByteBuf>().use { actual ->
+            Unpooled.wrappedBuffer(expected).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoderTest.kt
new file mode 100644
index 00000000..76f6aadb
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseDecoderTest.kt
@@ -0,0 +1,138 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import io.netty.handler.codec.DecoderException
+import org.junit.jupiter.api.assertThrows
+import org.openrs2.buffer.use
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Js5ResponseDecoderTest {
+    @Test
+    fun testDecode() {
+        testDecode("508.dat", "508-prefetch.dat", true)
+        testDecode("508.dat", "508-urgent.dat", false)
+
+        testDecode("509.dat", "509-prefetch.dat", true)
+        testDecode("509.dat", "509-urgent.dat", false)
+
+        testDecode("1019.dat", "1019-prefetch.dat", true)
+        testDecode("1019.dat", "1019-urgent.dat", false)
+
+        testDecode("1020.dat", "1020-prefetch.dat", true)
+        testDecode("1020.dat", "1020-urgent.dat", false)
+
+        testDecode("1530.dat", "1530-prefetch.dat", true)
+        testDecode("1530.dat", "1530-urgent.dat", false)
+
+        testDecode("1531.dat", "1531-prefetch.dat", true)
+        testDecode("1531.dat", "1531-urgent.dat", false)
+    }
+
+    @Test
+    fun testDecodeFragmented() {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        channel.writeInbound(Unpooled.wrappedBuffer(byteArrayOf(2, 0, 3, 0, 0, 0, 0)))
+        channel.writeInbound(
+            Unpooled.wrappedBuffer(
+                byteArrayOf(
+                    7,
+                    'O'.toByte(),
+                    'p'.toByte(),
+                    'e'.toByte(),
+                    'n'.toByte()
+                )
+            )
+        )
+        channel.writeInbound(Unpooled.wrappedBuffer(byteArrayOf('R'.toByte(), 'S'.toByte(), '2'.toByte())))
+
+        Unpooled.buffer().use { buf ->
+            buf.writeByte(0)
+            buf.writeInt(7)
+            buf.writeCharSequence("OpenRS2", Charsets.UTF_8)
+
+            val expected = Js5Response(false, 2, 3, buf)
+
+            channel.readInbound<Js5Response>().use { actual ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+
+    @Test
+    fun testDecodeNegativeLength() {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(
+                Unpooled.wrappedBuffer(
+                    byteArrayOf(
+                        2, 0, 3, 0, 0xFF.toByte(), 0xFF.toByte(), 0xFF.toByte(), 0xFF.toByte()
+                    )
+                )
+            )
+        }
+    }
+
+    @Test
+    fun testDecodeOverflowUncompressed() {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(
+                Unpooled.wrappedBuffer(
+                    byteArrayOf(
+                        2, 0, 3, 0, 0x7F, 0xFF.toByte(), 0xFF.toByte(), 0xFB.toByte()
+                    )
+                )
+            )
+        }
+    }
+
+    @Test
+    fun testDecodeOverflowCompressed() {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(
+                Unpooled.wrappedBuffer(
+                    byteArrayOf(
+                        2, 0, 3, 1, 0x7F, 0xFF.toByte(), 0xFF.toByte(), 0xF7.toByte()
+                    )
+                )
+            )
+        }
+    }
+
+    @Test
+    fun testDecodeInvalidBlockTrailer() {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        assertThrows<DecoderException> {
+            channel.writeInbound(read("invalid-block-trailer.dat"))
+        }
+    }
+
+    private fun testDecode(container: String, encoded: String, prefetch: Boolean) {
+        val channel = EmbeddedChannel(Js5ResponseDecoder())
+
+        channel.writeInbound(read(encoded))
+
+        read(container).use { data ->
+            val expected = Js5Response(prefetch, 2, 3, data)
+
+            channel.readInbound<Js5Response>().use { actual ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+
+    private fun read(name: String): ByteBuf {
+        Js5ResponseDecoderTest::class.java.getResourceAsStream(name).use { input ->
+            return Unpooled.wrappedBuffer(input.readAllBytes())
+        }
+    }
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoderTest.kt
new file mode 100644
index 00000000..d93da0c6
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/Js5ResponseEncoderTest.kt
@@ -0,0 +1,60 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import io.netty.handler.codec.EncoderException
+import org.junit.jupiter.api.assertThrows
+import org.openrs2.buffer.use
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object Js5ResponseEncoderTest {
+    @Test
+    fun testEncode() {
+        testEncode("508.dat", "508-prefetch.dat", true)
+        testEncode("508.dat", "508-urgent.dat", false)
+
+        testEncode("509.dat", "509-prefetch.dat", true)
+        testEncode("509.dat", "509-urgent.dat", false)
+
+        testEncode("1019.dat", "1019-prefetch.dat", true)
+        testEncode("1019.dat", "1019-urgent.dat", false)
+
+        testEncode("1020.dat", "1020-prefetch.dat", true)
+        testEncode("1020.dat", "1020-urgent.dat", false)
+
+        testEncode("1530.dat", "1530-prefetch.dat", true)
+        testEncode("1530.dat", "1530-urgent.dat", false)
+
+        testEncode("1531.dat", "1531-prefetch.dat", true)
+        testEncode("1531.dat", "1531-urgent.dat", false)
+    }
+
+    @Test
+    fun testEncodeEmpty() {
+        val channel = EmbeddedChannel(Js5ResponseEncoder())
+
+        assertThrows<EncoderException> {
+            channel.writeOutbound(Js5Response(true, 2, 3, Unpooled.EMPTY_BUFFER))
+        }
+    }
+
+    private fun testEncode(container: String, encoded: String, prefetch: Boolean) {
+        val channel = EmbeddedChannel(Js5ResponseEncoder())
+
+        read(container).use { buf ->
+            channel.writeOutbound(Js5Response(prefetch, 2, 3, buf.retain()))
+        }
+
+        read(encoded).use { expected ->
+            assertEquals(expected, channel.readOutbound())
+        }
+    }
+
+    private fun read(name: String): ByteBuf {
+        Js5ResponseEncoderTest::class.java.getResourceAsStream(name).use { input ->
+            return Unpooled.wrappedBuffer(input.readAllBytes())
+        }
+    }
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorDecoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorDecoderTest.kt
new file mode 100644
index 00000000..ffd51e3c
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorDecoderTest.kt
@@ -0,0 +1,40 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.PooledByteBufAllocator
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import org.openrs2.buffer.use
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object XorDecoderTest {
+    @Test
+    fun testDecode() {
+        testDecode(0, "OpenRS2", false)
+        testDecode(0, "OpenRS2", true)
+        testDecode(32, "oPENrs\u0012", false)
+        testDecode(32, "oPENrs\u0012", true)
+    }
+
+    private fun testDecode(key: Int, expected: String, direct: Boolean) {
+        val decoder = XorDecoder()
+        decoder.key = key
+
+        val channel = EmbeddedChannel(decoder)
+        if (direct) {
+            PooledByteBufAllocator.DEFAULT.ioBuffer().use { buf ->
+                buf.writeBytes("OpenRS2".toByteArray())
+                channel.writeInbound(buf.retain())
+            }
+        } else {
+            channel.writeInbound(Unpooled.wrappedBuffer("OpenRS2".toByteArray()))
+        }
+
+        channel.readInbound<ByteBuf>().use { actual ->
+            Unpooled.wrappedBuffer(expected.toByteArray()).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+}
diff --git a/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorEncoderTest.kt b/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorEncoderTest.kt
new file mode 100644
index 00000000..04d77bae
--- /dev/null
+++ b/protocol/src/test/kotlin/org/openrs2/protocol/js5/XorEncoderTest.kt
@@ -0,0 +1,40 @@
+package org.openrs2.protocol.js5
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.PooledByteBufAllocator
+import io.netty.buffer.Unpooled
+import io.netty.channel.embedded.EmbeddedChannel
+import org.openrs2.buffer.use
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+object XorEncoderTest {
+    @Test
+    fun testEncode() {
+        testEncode(0, "OpenRS2", false)
+        testEncode(0, "OpenRS2", true)
+        testEncode(32, "oPENrs\u0012", false)
+        testEncode(32, "oPENrs\u0012", true)
+    }
+
+    private fun testEncode(key: Int, expected: String, direct: Boolean) {
+        val encoder = XorEncoder()
+        encoder.key = key
+
+        val channel = EmbeddedChannel(encoder)
+        if (direct) {
+            PooledByteBufAllocator.DEFAULT.ioBuffer().use { buf ->
+                buf.writeBytes("OpenRS2".toByteArray())
+                channel.writeOutbound(buf.retain())
+            }
+        } else {
+            channel.writeOutbound(Unpooled.wrappedBuffer("OpenRS2".toByteArray()))
+        }
+
+        channel.readOutbound<ByteBuf>().use { actual ->
+            Unpooled.wrappedBuffer(expected.toByteArray()).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+}
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1019-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1019-prefetch.dat
new file mode 100644
index 00000000..5d2ee5ce
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diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1019-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1019-urgent.dat
new file mode 100644
index 00000000..5efce678
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diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1019.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1019.dat
new file mode 100644
index 00000000..a8a624b6
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1019.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1020-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1020-prefetch.dat
new file mode 100644
index 00000000..7afdc6b3
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diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1020-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1020-urgent.dat
new file mode 100644
index 00000000..57aa6a81
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1020-urgent.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1020.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1020.dat
new file mode 100644
index 00000000..81dfca87
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1020.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1530-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1530-prefetch.dat
new file mode 100644
index 00000000..eee39ab8
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1530-prefetch.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1530-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1530-urgent.dat
new file mode 100644
index 00000000..22c4d38a
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1530-urgent.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1530.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1530.dat
new file mode 100644
index 00000000..af31cb74
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1530.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1531-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1531-prefetch.dat
new file mode 100644
index 00000000..fe8e66b4
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1531-prefetch.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1531-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1531-urgent.dat
new file mode 100644
index 00000000..09993f12
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1531-urgent.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/1531.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/1531.dat
new file mode 100644
index 00000000..04ad5cff
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/1531.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/508-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/508-prefetch.dat
new file mode 100644
index 00000000..baed755c
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/508-prefetch.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/508-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/508-urgent.dat
new file mode 100644
index 00000000..040ac8bd
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/508-urgent.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/508.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/508.dat
new file mode 100644
index 00000000..6500e76c
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/508.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/509-prefetch.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/509-prefetch.dat
new file mode 100644
index 00000000..8b7b5f6e
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/509-prefetch.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/509-urgent.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/509-urgent.dat
new file mode 100644
index 00000000..d97c7967
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/509-urgent.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/509.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/509.dat
new file mode 100644
index 00000000..c94b5e7a
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/509.dat differ
diff --git a/protocol/src/test/resources/org/openrs2/protocol/js5/invalid-block-trailer.dat b/protocol/src/test/resources/org/openrs2/protocol/js5/invalid-block-trailer.dat
new file mode 100644
index 00000000..2450d775
Binary files /dev/null and b/protocol/src/test/resources/org/openrs2/protocol/js5/invalid-block-trailer.dat differ
diff --git a/settings.gradle.kts b/settings.gradle.kts
index d189456a..1d8c3ac8 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -28,6 +28,7 @@ include(
     "nonfree:signlink",
     "nonfree:unpack",
     "nonfree:unpackclass",
+    "protocol",
     "util",
     "yaml"
 )