diff --git a/IMPLEMENTATION.md b/IMPLEMENTATION.md
index 3fe5978..15c5624 100644
--- a/IMPLEMENTATION.md
+++ b/IMPLEMENTATION.md
@@ -33,7 +33,7 @@ When working through this file, mark increments complete by changing `[ ]` to `[
 
 Each type lives in `src/FrameProcessor/Domain/`. Tests in `tests/FrameProcessor.Tests/`.
 
-### [ ] 1.1 `MacAddress`
+### [x] 1.1 `MacAddress`
 - `record struct` storing 6 bytes.
 - `static bool TryParse(string, out MacAddress)` accepting `AA:BB:CC:DD:EE:FF`, `aa-bb-cc-dd-ee-ff`, `AABBCCDDEEFF`, surrounding whitespace.
 - `ToString()` → canonical lowercase no-separator (`aabbccddeeff`).
diff --git a/src/FrameProcessor/Domain/MacAddress.cs b/src/FrameProcessor/Domain/MacAddress.cs
new file mode 100644
index 0000000..ebb88bc
--- /dev/null
+++ b/src/FrameProcessor/Domain/MacAddress.cs
@@ -0,0 +1,156 @@
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace FrameProcessor.Domain;
+
+/// <summary>
+/// A 48-bit MAC address. Canonical form is lowercase hex without separators (e.g. <c>aabbccddeeff</c>);
+/// parsing accepts colon, hyphen, or unseparated hex with arbitrary surrounding whitespace.
+/// </summary>
+[JsonConverter(typeof(MacAddressJsonConverter))]
+public readonly record struct MacAddress : IParsable<MacAddress>, ISpanParsable<MacAddress>
+{
+    private readonly byte _b0;
+    private readonly byte _b1;
+    private readonly byte _b2;
+    private readonly byte _b3;
+    private readonly byte _b4;
+    private readonly byte _b5;
+
+    public MacAddress(ReadOnlySpan<byte> bytes)
+    {
+        if (bytes.Length != 6)
+        {
+            throw new ArgumentException("MAC address must be exactly 6 bytes.", nameof(bytes));
+        }
+
+        _b0 = bytes[0];
+        _b1 = bytes[1];
+        _b2 = bytes[2];
+        _b3 = bytes[3];
+        _b4 = bytes[4];
+        _b5 = bytes[5];
+    }
+
+    public override string ToString() => string.Create(12, this, static (span, mac) =>
+    {
+        WriteHex(span[..2], mac._b0);
+        WriteHex(span.Slice(2, 2), mac._b1);
+        WriteHex(span.Slice(4, 2), mac._b2);
+        WriteHex(span.Slice(6, 2), mac._b3);
+        WriteHex(span.Slice(8, 2), mac._b4);
+        WriteHex(span.Slice(10, 2), mac._b5);
+    });
+
+    public static bool TryParse(string? s, out MacAddress result)
+    {
+        if (s is null)
+        {
+            result = default;
+            return false;
+        }
+
+        return TryParse(s.AsSpan(), out result);
+    }
+
+    public static bool TryParse(ReadOnlySpan<char> s, out MacAddress result)
+    {
+        result = default;
+        s = s.Trim();
+        if (s.IsEmpty)
+        {
+            return false;
+        }
+
+        Span<char> hex = stackalloc char[12];
+        var written = 0;
+        foreach (var c in s)
+        {
+            if (c is ':' or '-')
+            {
+                continue;
+            }
+
+            if (written == 12)
+            {
+                return false;
+            }
+
+            if (!IsHexDigit(c))
+            {
+                return false;
+            }
+
+            hex[written++] = c;
+        }
+
+        if (written != 12)
+        {
+            return false;
+        }
+
+        Span<byte> bytes = stackalloc byte[6];
+        for (var i = 0; i < 6; i++)
+        {
+            if (!byte.TryParse(hex.Slice(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var b))
+            {
+                return false;
+            }
+
+            bytes[i] = b;
+        }
+
+        result = new MacAddress(bytes);
+        return true;
+    }
+
+    public static MacAddress Parse(string s)
+    {
+        ArgumentNullException.ThrowIfNull(s);
+        return TryParse(s, out var result)
+            ? result
+            : throw new FormatException($"'{s}' is not a valid MAC address.");
+    }
+
+    public static MacAddress Parse(string s, IFormatProvider? provider) => Parse(s);
+
+    public static bool TryParse(string? s, IFormatProvider? provider, out MacAddress result)
+        => TryParse(s, out result);
+
+    public static MacAddress Parse(ReadOnlySpan<char> s, IFormatProvider? provider)
+        => TryParse(s, out var result)
+            ? result
+            : throw new FormatException($"'{s}' is not a valid MAC address.");
+
+    public static bool TryParse(ReadOnlySpan<char> s, IFormatProvider? provider, out MacAddress result)
+        => TryParse(s, out result);
+
+    private static bool IsHexDigit(char c)
+        => (uint)(c - '0') <= 9 || (uint)(c - 'a') <= 5 || (uint)(c - 'A') <= 5;
+
+    private static void WriteHex(Span<char> dest, byte value)
+    {
+        dest[0] = HexChar(value >> 4);
+        dest[1] = HexChar(value & 0xF);
+    }
+
+    private static char HexChar(int nibble) => (char)(nibble < 10 ? '0' + nibble : 'a' + (nibble - 10));
+}
+
+internal sealed class MacAddressJsonConverter : JsonConverter<MacAddress>
+{
+    public override MacAddress Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        var s = reader.GetString();
+        if (!MacAddress.TryParse(s, out var mac))
+        {
+            throw new JsonException($"'{s}' is not a valid MAC address.");
+        }
+
+        return mac;
+    }
+
+    public override void Write(Utf8JsonWriter writer, MacAddress value, JsonSerializerOptions options)
+        => writer.WriteStringValue(value.ToString());
+}
diff --git a/tests/FrameProcessor.Tests/MacAddressTests.cs b/tests/FrameProcessor.Tests/MacAddressTests.cs
new file mode 100644
index 0000000..56ae400
--- /dev/null
+++ b/tests/FrameProcessor.Tests/MacAddressTests.cs
@@ -0,0 +1,112 @@
+using System.Text.Json;
+using FrameProcessor.Domain;
+
+namespace FrameProcessor.Tests;
+
+public class MacAddressTests
+{
+    private static readonly byte[] ExpectedBytes = [0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF];
+    private const string Canonical = "aabbccddeeff";
+
+    [Theory]
+    [InlineData("AA:BB:CC:DD:EE:FF")]
+    [InlineData("aa:bb:cc:dd:ee:ff")]
+    [InlineData("AA-BB-CC-DD-EE-FF")]
+    [InlineData("aa-bb-cc-dd-ee-ff")]
+    [InlineData("AABBCCDDEEFF")]
+    [InlineData("aabbccddeeff")]
+    [InlineData("  AA:BB:CC:DD:EE:FF  ")]
+    [InlineData("\tAA-bb-CC-dd-EE-ff\n")]
+    public void TryParse_AcceptedForms_ProduceCanonicalString(string input)
+    {
+        Assert.True(MacAddress.TryParse(input, out var mac));
+        Assert.Equal(Canonical, mac.ToString());
+    }
+
+    [Fact]
+    public void Equality_IsByteWise_AcrossInputForms()
+    {
+        Assert.True(MacAddress.TryParse("AA:BB:CC:DD:EE:FF", out var a));
+        Assert.True(MacAddress.TryParse("aa-bb-cc-dd-ee-ff", out var b));
+        Assert.True(MacAddress.TryParse("AABBCCDDEEFF", out var c));
+
+        Assert.Equal(a, b);
+        Assert.Equal(b, c);
+        Assert.Equal(a.GetHashCode(), b.GetHashCode());
+    }
+
+    [Fact]
+    public void Equality_DiffersOnAnySingleByte()
+    {
+        Assert.True(MacAddress.TryParse("aabbccddeeff", out var a));
+        Assert.True(MacAddress.TryParse("aabbccddeefe", out var b));
+
+        Assert.NotEqual(a, b);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("not-a-mac")]
+    [InlineData("AA:BB:CC:DD:EE")]              // too short
+    [InlineData("AA:BB:CC:DD:EE:FF:00")]        // too long
+    [InlineData("ZZ:BB:CC:DD:EE:FF")]           // non-hex digit
+    [InlineData("AA:BB:CC:DD:EE:F")]            // odd hex count
+    [InlineData("AA BB CC DD EE FF")]           // unsupported space separator
+    public void TryParse_RejectsBadInput(string input)
+    {
+        Assert.False(MacAddress.TryParse(input, out _));
+    }
+
+    [Fact]
+    public void TryParse_Null_ReturnsFalse()
+    {
+        Assert.False(MacAddress.TryParse((string?)null, out _));
+    }
+
+    [Fact]
+    public void Parse_Throws_OnBadInput()
+    {
+        Assert.Throws<FormatException>(() => MacAddress.Parse("nope"));
+    }
+
+    [Fact]
+    public void Constructor_FromBytes_RoundTripsThroughToString()
+    {
+        var mac = new MacAddress(ExpectedBytes);
+        Assert.Equal(Canonical, mac.ToString());
+    }
+
+    [Fact]
+    public void Constructor_FromWrongLength_Throws()
+    {
+        Assert.Throws<ArgumentException>(() => new MacAddress(new byte[] { 0x00 }));
+        Assert.Throws<ArgumentException>(() => new MacAddress(new byte[7]));
+    }
+
+    [Fact]
+    public void JsonRoundTrip_NormalizesToCanonicalForm()
+    {
+        var json = "\"AA:BB:CC:DD:EE:FF\"";
+        var mac = JsonSerializer.Deserialize<MacAddress>(json);
+        var written = JsonSerializer.Serialize(mac);
+
+        Assert.Equal($"\"{Canonical}\"", written);
+    }
+
+    [Fact]
+    public void JsonDeserialize_BadInput_Throws()
+    {
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<MacAddress>("\"not-a-mac\""));
+    }
+
+    [Fact]
+    public void IParsable_Hookup_Works()
+    {
+        var mac = MacAddress.Parse("AA:BB:CC:DD:EE:FF", provider: null);
+        Assert.Equal(Canonical, mac.ToString());
+
+        Assert.True(MacAddress.TryParse("AA:BB:CC:DD:EE:FF", provider: null, out var mac2));
+        Assert.Equal(mac, mac2);
+    }
+}
diff --git a/tests/FrameProcessor.Tests/UnitTest1.cs b/tests/FrameProcessor.Tests/UnitTest1.cs
index 5b2f905..e43dfbc 100644
--- a/tests/FrameProcessor.Tests/UnitTest1.cs
+++ b/tests/FrameProcessor.Tests/UnitTest1.cs
@@ -1,10 +1 @@
-namespace FrameProcessor.Tests;
-
-public class UnitTest1
-{
-    [Fact]
-    public void Test1()
-    {
-
-    }
-}
+namespace FrameProcessor.Tests;