diff --git a/09/input b/09/input
new file mode 100644
index 0000000..9a7fcf5
--- /dev/null
+++ b/09/input
@@ -0,0 +1,496 @@
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diff --git a/09/main.go b/09/main.go
new file mode 100644
index 0000000..37a1ec6
--- /dev/null
+++ b/09/main.go
@@ -0,0 +1,50 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"strings"
+
+	"git.z1glr.de/advent-of-code-2025/pkg/aoc"
+)
+
+type Point struct {
+	X, Y int
+}
+
+func (p Point) Area(p2 Point) float64 {
+	return math.Abs(float64((p.X - p2.X + 1) * (p.Y - p2.Y + 1)))
+}
+
+func do(test bool) (int, int) {
+	rows := aoc.ReadFileRows(test)
+
+	points := make([]Point, len(rows))
+
+	for ii, rr := range rows {
+		parts := strings.Split(rr, ",")
+
+		points[ii] = Point{
+			X: aoc.ParseInt(parts[0]),
+			Y: aoc.ParseInt(parts[1]),
+		}
+	}
+
+	largestArea := 0.0
+
+	for ii, p1 := range points {
+		for _, p2 := range points[ii+1:] {
+			largestArea = math.Max(largestArea, p1.Area(p2))
+		}
+	}
+
+	fmt.Printf("%9.0f\n", largestArea)
+
+	return int(largestArea), 0
+}
+
+func main() {
+	if r1, r2 := do(true); r1 == 50 && r2 == 0 {
+		do(false)
+	}
+}
diff --git a/09/test b/09/test
new file mode 100644
index 0000000..c8563ea
--- /dev/null
+++ b/09/test
@@ -0,0 +1,8 @@
+7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3