diff --git a/packages/utils/src/__tests__/BinaryReader.test.ts b/packages/utils/src/__tests__/BinaryReader.test.ts
new file mode 100644
index 0000000..e4ddd4a
--- /dev/null
+++ b/packages/utils/src/__tests__/BinaryReader.test.ts
@@ -0,0 +1,325 @@
+import { beforeEach, describe, expect, it } from 'vitest';
+import { BinaryReader } from '../BinaryReader';
+import { BinaryWriter } from '../BinaryWriter';
+
+const concatBuffers = (...parts: ArrayBuffer[]): ArrayBuffer =>
+{
+    const total = parts.reduce((sum, part) => sum + part.byteLength, 0);
+    const out = new Uint8Array(total);
+    let offset = 0;
+
+    for(const part of parts)
+    {
+        out.set(new Uint8Array(part), offset);
+        offset += part.byteLength;
+    }
+
+    return out.buffer;
+};
+
+describe('BinaryReader / BinaryWriter', () =>
+{
+    let writer: BinaryWriter;
+
+    beforeEach(() =>
+    {
+        writer = new BinaryWriter();
+    });
+
+    describe('byte round-trip', () =>
+    {
+        it('writes and reads a single byte', () =>
+        {
+            writer.writeByte(0x42);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readByte()).toBe(0x42);
+            expect(reader.remaining()).toBe(0);
+        });
+
+        it('readByte returns a signed int8 (values above 127 wrap negative)', () =>
+        {
+            writer.writeByte(0xFF);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readByte()).toBe(-1);
+        });
+
+        it('writeByte chains', () =>
+        {
+            writer.writeByte(1).writeByte(2).writeByte(3);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readByte()).toBe(1);
+            expect(reader.readByte()).toBe(2);
+            expect(reader.readByte()).toBe(3);
+        });
+    });
+
+    describe('short round-trip (16-bit big-endian)', () =>
+    {
+        it('writes and reads a positive short', () =>
+        {
+            writer.writeShort(0x1234);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readShort()).toBe(0x1234);
+        });
+
+        it('round-trips the int16 boundary values', () =>
+        {
+            writer.writeShort(32767).writeShort(-1);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readShort()).toBe(32767);
+            expect(reader.readShort()).toBe(-1);
+        });
+
+        it('emits big-endian byte order', () =>
+        {
+            writer.writeShort(0x0102);
+
+            const bytes = new Uint8Array(writer.getBuffer());
+
+            expect(bytes[0]).toBe(0x01);
+            expect(bytes[1]).toBe(0x02);
+        });
+    });
+
+    describe('int round-trip (32-bit big-endian)', () =>
+    {
+        it('writes and reads a positive int', () =>
+        {
+            writer.writeInt(123456789);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readInt()).toBe(123456789);
+        });
+
+        it('round-trips the int32 boundaries (max / min / -1)', () =>
+        {
+            writer.writeInt(2147483647).writeInt(-2147483648).writeInt(-1);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readInt()).toBe(2147483647);
+            expect(reader.readInt()).toBe(-2147483648);
+            expect(reader.readInt()).toBe(-1);
+        });
+
+        it('emits big-endian byte order', () =>
+        {
+            writer.writeInt(0x01020304);
+
+            const bytes = new Uint8Array(writer.getBuffer());
+
+            expect(bytes[0]).toBe(0x01);
+            expect(bytes[1]).toBe(0x02);
+            expect(bytes[2]).toBe(0x03);
+            expect(bytes[3]).toBe(0x04);
+        });
+    });
+
+    describe('string round-trip', () =>
+    {
+        it('writes a length-prefixed string and decodes it back via readShort + readBytes', () =>
+        {
+            writer.writeString('hello');
+
+            const reader = new BinaryReader(writer.getBuffer());
+            const length = reader.readShort();
+
+            expect(length).toBe(5);
+            expect(reader.readBytes(length).toString()).toBe('hello');
+        });
+
+        it('round-trips UTF-8 multibyte characters with correct byte length', () =>
+        {
+            // 'café' = 5 bytes UTF-8 (c, a, 0xC3 0xA9, ASCII finale)
+            writer.writeString('café');
+
+            const reader = new BinaryReader(writer.getBuffer());
+            const length = reader.readShort();
+
+            expect(length).toBe(5);
+            expect(reader.readBytes(length).toString()).toBe('café');
+        });
+
+        it('writeString with includeLength=false omits the length prefix', () =>
+        {
+            writer.writeString('xy', false);
+
+            const buf = writer.getBuffer();
+
+            expect(buf.byteLength).toBe(2);
+            expect(new Uint8Array(buf)[0]).toBe(0x78); // 'x'
+            expect(new Uint8Array(buf)[1]).toBe(0x79); // 'y'
+        });
+
+        it('round-trips the empty string', () =>
+        {
+            writer.writeString('');
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readShort()).toBe(0);
+            expect(reader.remaining()).toBe(0);
+        });
+    });
+
+    describe('writeBytes', () =>
+    {
+        it('appends a number[] payload', () =>
+        {
+            writer.writeBytes([ 0x10, 0x20, 0x30 ]);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readByte()).toBe(0x10);
+            expect(reader.readByte()).toBe(0x20);
+            expect(reader.readByte()).toBe(0x30);
+        });
+
+        it('appends an ArrayBuffer payload', () =>
+        {
+            const payload = new Uint8Array([ 0xAA, 0xBB ]).buffer;
+
+            writer.writeBytes(payload);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readByte()).toBe(-86); // 0xAA as int8
+            expect(reader.readByte()).toBe(-69); // 0xBB as int8
+        });
+    });
+
+    describe('readBytes slice', () =>
+    {
+        it('returns an independent reader over the requested slice', () =>
+        {
+            writer.writeInt(0xCAFEBABE | 0).writeInt(0xDEADBEEF | 0);
+
+            const reader = new BinaryReader(writer.getBuffer());
+            const sliced = reader.readBytes(4);
+
+            // The slice's position is independent of the outer reader.
+            expect(sliced.readInt()).toBe(0xCAFEBABE | 0);
+            // The outer reader advanced by 4 and can still read the second int.
+            expect(reader.readInt()).toBe(0xDEADBEEF | 0);
+        });
+    });
+
+    describe('remaining accounting', () =>
+    {
+        it('decrements by the read size and reaches 0 at the end of the buffer', () =>
+        {
+            writer.writeByte(1).writeShort(2).writeInt(3);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.remaining()).toBe(7);
+
+            reader.readByte();
+            expect(reader.remaining()).toBe(6);
+
+            reader.readShort();
+            expect(reader.remaining()).toBe(4);
+
+            reader.readInt();
+            expect(reader.remaining()).toBe(0);
+        });
+    });
+
+    describe('float / double read', () =>
+    {
+        // BinaryWriter has no write counterparts for float/double — build the
+        // buffer by hand via DataView and check the reader decodes correctly.
+
+        it('readFloat decodes an IEEE-754 single-precision big-endian value', () =>
+        {
+            const buf = new ArrayBuffer(4);
+            new DataView(buf).setFloat32(0, 3.5, false);
+
+            const reader = new BinaryReader(buf);
+
+            expect(reader.readFloat()).toBeCloseTo(3.5, 5);
+            expect(reader.remaining()).toBe(0);
+        });
+
+        it('readDouble decodes an IEEE-754 double-precision big-endian value', () =>
+        {
+            const buf = new ArrayBuffer(8);
+            new DataView(buf).setFloat64(0, Math.PI, false);
+
+            const reader = new BinaryReader(buf);
+
+            expect(reader.readDouble()).toBeCloseTo(Math.PI, 12);
+            expect(reader.remaining()).toBe(0);
+        });
+    });
+
+    describe('writer position getter/setter', () =>
+    {
+        it('reports the position after writes', () =>
+        {
+            writer.writeInt(0).writeShort(0);
+
+            expect(writer.position).toBe(6);
+        });
+
+        it('position can be set explicitly (caller-managed reposition)', () =>
+        {
+            writer.writeInt(0);
+            writer.position = 0;
+
+            expect(writer.position).toBe(0);
+        });
+    });
+
+    describe('typical packet round-trip (header + payload)', () =>
+    {
+        it('encodes and decodes a header + mixed payload (short + int + string)', () =>
+        {
+            const header = 1234;
+            const userId = 99999;
+            const username = 'simoleo';
+
+            writer
+                .writeShort(header)
+                .writeInt(userId)
+                .writeString(username);
+
+            const reader = new BinaryReader(writer.getBuffer());
+
+            expect(reader.readShort()).toBe(header);
+            expect(reader.readInt()).toBe(userId);
+
+            const nameLength = reader.readShort();
+            const name = reader.readBytes(nameLength).toString();
+
+            expect(name).toBe(username);
+            expect(reader.remaining()).toBe(0);
+        });
+
+        it('concatenated buffers round-trip across independent writer instances', () =>
+        {
+            const a = new BinaryWriter();
+            const b = new BinaryWriter();
+
+            a.writeInt(11);
+            b.writeInt(22);
+
+            const reader = new BinaryReader(concatBuffers(a.getBuffer(), b.getBuffer()));
+
+            expect(reader.readInt()).toBe(11);
+            expect(reader.readInt()).toBe(22);
+            expect(reader.remaining()).toBe(0);
+        });
+    });
+});