diff --git a/day-3/go.mod b/day-3/go.mod
new file mode 100644
index 0000000..0604fa0
--- /dev/null
+++ b/day-3/go.mod
@@ -0,0 +1,5 @@
+module github.com/onyx-and-iris/aoc2023/day-3
+
+go 1.20
+
+require github.com/go-playground/assert/v2 v2.2.0
diff --git a/day-3/go.sum b/day-3/go.sum
new file mode 100644
index 0000000..1998fd7
--- /dev/null
+++ b/day-3/go.sum
@@ -0,0 +1,2 @@
+github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
+github.com/go-playground/assert/v2 v2.2.0/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4=
diff --git a/day-3/one.go b/day-3/one.go
new file mode 100644
index 0000000..e49c8dc
--- /dev/null
+++ b/day-3/one.go
@@ -0,0 +1,117 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"unicode"
+)
+
+var symbols = [][]bool{}
+
+// enginePart represents a single engine part
+type enginePart struct {
+	digits []digit
+}
+
+// realValue returns the numeric value of all digits combined
+func (e *enginePart) realValue() (int, error) {
+	var numStr string
+	for _, digit := range e.digits {
+		numStr += fmt.Sprintf("%d", digit.raw)
+	}
+	n, err := strconv.Atoi(numStr)
+	if err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
+// digit represents a single digit in an engine part
+type digit struct {
+	row  int
+	col  int
+	raw  int
+	pass bool
+}
+
+// checkDigit checks if any neighbouring characters are true (in symbol matrix)
+func checkDigit(d digit) digit {
+	i := d.col - 1
+	for ; i < len(symbols[d.row]) && i <= d.col+1; i += 1 {
+		if i < 0 {
+			continue
+		}
+		if d.row != 0 {
+			if symbols[d.row-1][i] {
+				d.pass = true
+				break
+			}
+		}
+		if symbols[d.row][i] {
+			d.pass = true
+			break
+		}
+		if d.row != len(symbols)-1 {
+			if symbols[d.row+1][i] {
+				d.pass = true
+				break
+			}
+		}
+	}
+	return d
+}
+
+// checkDigits runs each digit in an engine part through checkDigit()
+func checkDigits(i, j int, line string) (int, int, error) {
+	enginePart := enginePart{}
+	for ; j < len(line); j += 1 {
+		if !unicode.IsNumber(rune(line[j])) {
+			break
+		}
+		enginePart.digits = append(enginePart.digits, checkDigit(digit{row: i, col: j, raw: int(line[j]) - '0', pass: false}))
+	}
+
+	if anyTrue(enginePart.digits) {
+		engineParts[i] = append(engineParts[i], enginePart)
+		n, err := enginePart.realValue()
+		if err != nil {
+			return 0, 0, err
+		}
+		return j, n, nil
+	}
+	return j, 0, nil
+}
+
+// symbolToBool generates a boolean matrix that represents the placement of symbols
+func symbolToBool(line string) []bool {
+	bool_arr := []bool{}
+	for _, c := range line {
+		bool_arr = append(bool_arr, !(unicode.IsNumber(c) || c == '.'))
+	}
+	return bool_arr
+}
+
+// one deciphers which numbers represent engine parts
+// it returns the sum of all engine parts
+func one(lines []string) (int, error) {
+	for _, line := range lines {
+		symbols = append(symbols, symbolToBool(line))
+	}
+	engineParts = make([][]enginePart, len(lines))
+
+	sum := 0
+	for i, line := range lines {
+		for j := 0; j < len(line); j += 1 {
+			if unicode.IsNumber(rune(line[j])) {
+				next, n, err := checkDigits(i, j, line)
+				if err != nil {
+					return 0, err
+				}
+				sum += n
+				j = next
+			}
+		}
+	}
+
+	return sum, nil
+}
diff --git a/day-3/one_test.go b/day-3/one_test.go
new file mode 100644
index 0000000..97265cc
--- /dev/null
+++ b/day-3/one_test.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/go-playground/assert/v2"
+)
+
+func TestSymbolToBool(t *testing.T) {
+	//t.Skip("skipping test")
+	input := []string{
+		"467..114..",
+		"...*......",
+		"..35..633.",
+		"......#...",
+	}
+
+	expected := [][]bool{
+		{false, false, false, false, false, false, false, false, false, false},
+		{false, false, false, true, false, false, false, false, false, false},
+		{false, false, false, false, false, false, false, false, false, false},
+		{false, false, false, false, false, false, true, false, false, false},
+	}
+
+	bool_matrix := [][]bool{}
+	for _, line := range input {
+		bool_matrix = append(bool_matrix, symbolToBool(line))
+	}
+
+	t.Run("Should produce equal boolean matrices", func(t *testing.T) {
+		assert.Equal(t, expected, bool_matrix)
+	})
+}
+
+func TestCheckDigit(t *testing.T) {
+	//t.Skip("skipping test")
+}
diff --git a/day-3/run.sh b/day-3/run.sh
new file mode 100755
index 0000000..3f6776a
--- /dev/null
+++ b/day-3/run.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+INPUT="input.txt"
+
+cat $INPUT | go run .
\ No newline at end of file
diff --git a/day-3/solution.go b/day-3/solution.go
new file mode 100644
index 0000000..3ea39e6
--- /dev/null
+++ b/day-3/solution.go
@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+func main() {
+	lines := readlines()
+
+	ans, err := one(lines)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("solution one: %d\n", ans)
+
+	ans, err = two(lines)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("solution two: %d\n", ans)
+}
diff --git a/day-3/two.go b/day-3/two.go
new file mode 100644
index 0000000..c4b0723
--- /dev/null
+++ b/day-3/two.go
@@ -0,0 +1,55 @@
+package main
+
+var engineParts [][]enginePart
+
+// getGearRatio returns the product of engine parts if exactly two neighbour a gear
+func getGearRatio(row, col int) (int, error) {
+	partsConsidered := []enginePart{}
+
+	i := row - 1
+	for ; i < len(engineParts) && i <= row+1; i += 1 {
+		if i < 0 {
+			continue
+		}
+		for _, enginePart := range engineParts[i] {
+			for _, part := range enginePart.digits {
+				if part.col == col-1 || part.col == col || part.col == col+1 {
+					if anyTrue(enginePart.digits) {
+						partsConsidered = append(partsConsidered, enginePart)
+						break
+					}
+				}
+			}
+		}
+	}
+	if len(partsConsidered) == 2 {
+		n1, err := partsConsidered[0].realValue()
+		if err != nil {
+			return 0, err
+		}
+		n2, err := partsConsidered[1].realValue()
+		if err != nil {
+			return 0, err
+		}
+		return n1 * n2, nil
+	}
+	return 0, nil
+}
+
+// two returns the sum of all gear ratios
+func two(lines []string) (int, error) {
+	sum := 0
+	for i, line := range lines {
+		for j, c := range line {
+			if rune(c) == '*' {
+				n, err := getGearRatio(i, j)
+				if err != nil {
+					return 0, err
+				}
+				sum += n
+			}
+		}
+	}
+
+	return sum, nil
+}
diff --git a/day-3/util.go b/day-3/util.go
new file mode 100644
index 0000000..d0c53d3
--- /dev/null
+++ b/day-3/util.go
@@ -0,0 +1,34 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+)
+
+// readlines reads lines from stdin.
+// Then it returns them as an array of strings
+func readlines() []string {
+	lines := []string{}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		log.Fatal(err)
+	}
+
+	return lines
+}
+
+// anyTrue checks if any digits passed
+func anyTrue(digits []digit) bool {
+	for _, digit := range digits {
+		if digit.pass {
+			return true
+		}
+	}
+	return false
+}