diff --git a/16/main.go b/16/main.go
new file mode 100644
index 0000000..e89d830
--- /dev/null
+++ b/16/main.go
@@ -0,0 +1,154 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+var hexMap = map[rune][]uint8{
+	'0': {0, 0, 0, 0},
+	'1': {0, 0, 0, 1},
+	'2': {0, 0, 1, 0},
+	'3': {0, 0, 1, 1},
+	'4': {0, 1, 0, 0},
+	'5': {0, 1, 0, 1},
+	'6': {0, 1, 1, 0},
+	'7': {0, 1, 1, 1},
+	'8': {1, 0, 0, 0},
+	'9': {1, 0, 0, 1},
+	'A': {1, 0, 1, 0},
+	'B': {1, 0, 1, 1},
+	'C': {1, 1, 0, 0},
+	'D': {1, 1, 0, 1},
+	'E': {1, 1, 1, 0},
+	'F': {1, 1, 1, 1},
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+func parseNumber(stream []uint8, length int) int64 {
+	result := int64(0)
+	for i := 0; i < length; i++ {
+		result += int64(stream[i]) << (length - 1 - i)
+	}
+	return result
+}
+
+type packet struct {
+	version       int64
+	typeID        int64
+	subPackets    []packet
+	encodedNumber int64
+}
+
+func getPacketVersion(stream []uint8) int64 {
+	return parseNumber(stream, 3)
+}
+
+func getPacketType(stream []uint8) int64 {
+	return parseNumber(stream, 3)
+}
+
+func getSubpacketLength(t uint8, stream []uint8) (int, int64) {
+	if t == 0 {
+		return 15, parseNumber(stream, 15)
+	}
+	if t == 1 {
+		return 11, parseNumber(stream, 11)
+	}
+	return 0, 0
+}
+
+func parsePayload(stream []uint8) (int64, int) {
+	num := []uint8{}
+	pos := 0
+	chars := 0
+	for {
+		currentsegment := stream[pos : pos+5]
+		chars += 4
+		num = append(num, currentsegment[1:5]...)
+		pos += 5
+		if currentsegment[0] == 0 {
+			break
+		}
+	}
+	return parseNumber(num, chars), pos
+}
+
+func parsePackets(stream []uint8) (int, []packet) {
+	if len(stream) <= 7 {
+		return 0, []packet{}
+	}
+	parsedPacket := packet{}
+	parsedPacket.version = getPacketVersion(stream[0:3])
+	parsedPacket.typeID = getPacketType(stream[3:6])
+	if parsedPacket.typeID == 4 {
+		encoded, consumed := parsePayload(stream[6:])
+		parsedPacket.encodedNumber = encoded
+		return consumed + 6, []packet{parsedPacket} // 6 is packet header length
+	} else {
+		parsed := 0
+		size, subpacketlength := getSubpacketLength(stream[6], stream[7:])
+		for {
+			consumed, subs := parsePackets(stream[7+size+parsed:])
+			parsedPacket.subPackets = append(parsedPacket.subPackets, subs...)
+			parsed += consumed
+			if size == 11 && int64(len(parsedPacket.subPackets)) == subpacketlength {
+				return parsed + 7 + size, []packet{parsedPacket}
+
+			} else if size == 15 && int64(parsed) > subpacketlength || consumed == 0 {
+				return parsed + 7 + size, []packet{parsedPacket}
+			}
+		}
+	}
+}
+
+func countVersions(packets []packet) int {
+	i := 0
+	for _, p := range packets {
+		i += int(p.version)
+		i += countVersions(p.subPackets)
+	}
+	return i
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	scanner.Scan()
+	line := scanner.Text()
+	stream := []uint8{}
+	for _, hex := range line {
+		stream = append(stream, hexMap[hex]...)
+	}
+	_, parsedPacket := parsePackets(stream)
+	fmt.Println(countVersions(parsedPacket))
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	for scanner.Scan() {
+		// line := scanner.Text()
+	}
+}
diff --git a/16/main_test.go b/16/main_test.go
new file mode 100644
index 0000000..cf060cb
--- /dev/null
+++ b/16/main_test.go
@@ -0,0 +1,61 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestVersionParse(t *testing.T) {
+	tests := map[int64][]uint8{
+		0: {0, 0, 0},
+		1: {0, 0, 1},
+		2: {0, 1, 0},
+		3: {0, 1, 1},
+		4: {1, 0, 0},
+		5: {1, 0, 1},
+		6: {1, 1, 0},
+		7: {1, 1, 1},
+	}
+	for result, input := range tests {
+		if result != getPacketVersion(input) {
+			t.Fail()
+		}
+		if result != getPacketType(input) {
+			t.Fail()
+		}
+	}
+}
+
+func TestParsePayload(t *testing.T) {
+	if n, q := parsePayload([]uint8{0, 1, 0, 1, 0}); n != 10 || q != 5 {
+		t.Log(n, q)
+		t.Fail()
+	}
+	if n, q := parsePayload([]uint8{1, 0, 0, 0, 1, 0, 0, 1, 0, 0}); n != 20 || q != 10 {
+		t.Log(n, q)
+		t.Fail()
+	}
+}
+
+func TestCases(t *testing.T) {
+	inputs := map[string]int{
+		"D2FE28":                         6,
+		"38006F45291200":                 9,
+		"EE00D40C823060":                 14,
+		"8A004A801A8002F478":             16,
+		"620080001611562C8802118E34":     12,
+		"C0015000016115A2E0802F182340":   23,
+		"A0016C880162017C3686B18A3D4780": 31,
+	}
+
+	for c, r := range inputs {
+		stream := []uint8{}
+		for _, hex := range c {
+			stream = append(stream, hexMap[hex]...)
+		}
+		_, parsedPacket := parsePackets(stream)
+		if r != countVersions(parsedPacket) {
+			t.Log(c, countVersions(parsedPacket))
+			t.Fail()
+		}
+	}
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..bd8ca58
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module adventofcode2021
+
+go 1.17
diff --git a/run.sh b/run.sh
index 2eeee27..dce9523 100755
--- a/run.sh
+++ b/run.sh
@@ -3,6 +3,6 @@
 if [ "${1}" != "" ]; then
     padded=$(printf "%02g" ${1})
     cd ${padded}
-    go run *.go
+    go run main.go
     cd - > /dev/null
 fi