diff --git a/2021/inputs/day13 b/2021/inputs/day13
new file mode 100644
index 0000000..8e56479
--- /dev/null
+++ b/2021/inputs/day13
@@ -0,0 +1,795 @@
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+
+fold along x=655
+fold along y=447
+fold along x=327
+fold along y=223
+fold along x=163
+fold along y=111
+fold along x=81
+fold along y=55
+fold along x=40
+fold along y=27
+fold along y=13
+fold along y=6
diff --git a/2021/src/bin/day13.rs b/2021/src/bin/day13.rs
new file mode 100644
index 0000000..142a5f4
--- /dev/null
+++ b/2021/src/bin/day13.rs
@@ -0,0 +1,123 @@
+#![feature(test)]
+extern crate test;
+use aoc2021::common::*;
+use itertools::Itertools;
+
+const DAY: usize = 13;
+type Parsed = (Vec<Vec<bool>>, Vec<Fold>);
+
+enum Fold {
+    X(usize),
+    Y(usize),
+}
+
+impl Fold {
+    fn fold(&self, grid: &mut Vec<Vec<bool>>) {
+        match *self {
+            Fold::X(at) => {
+                for x in 0..at {
+                    for y in 0..grid[x].len() {
+                        grid[x][y] |= grid[at + at - x][y];
+                    }
+                }
+                grid.truncate(at);
+            }
+            Fold::Y(at) => {
+                for ys in grid {
+                    for y in 0..at {
+                        ys[y] |= *ys.get(at + at - y).unwrap_or(&false);
+                    }
+                    ys.truncate(at);
+                }
+            }
+        }
+    }
+}
+
+fn parse_input(raw: &str) -> Parsed {
+    let (points, folds) = raw.split_once("\n\n").unwrap();
+    let points: Vec<(usize, usize)> =
+        points.lines().map(|line| line.split_once(',').unwrap()).map(|(x, y)| (parse_num(x), parse_num(y))).collect();
+    let mut grid = vec![vec![false; points.iter().map(|&(_, y)| y).max().unwrap() + 1]; points.iter().map(|&(x, _)| x).max().unwrap() + 1];
+    println!("allocated x {} and y {}", grid.len(), grid[0].len());
+    for (x, y) in points {
+        grid[x][y] = true;
+    }
+    let folds = folds
+        .lines()
+        .map(|line| {
+            if let Some(x) = line.strip_prefix("fold along x=") {
+                Fold::X(parse_num(x))
+            } else if let Some(y) = line.strip_prefix("fold along y=") {
+                Fold::Y(parse_num(y))
+            } else {
+                unreachable!("{}", line)
+            }
+        })
+        .collect();
+    (grid, folds)
+}
+
+fn part1((grid, folds): &Parsed) -> usize {
+    let mut folded = grid.to_owned();
+    folds[0].fold(&mut folded);
+    folded.into_iter().flatten().filter(|&b| b).count()
+}
+
+fn part2((grid, instructions): &Parsed) -> String {
+    let mut paper = grid.to_owned();
+    for instruction in instructions {
+        instruction.fold(&mut paper); // :thanking:
+    }
+    paper.into_iter().map(|ys| ys.into_iter().map(|b| if b { '#' } else { ' ' }).collect::<String>()).join("\n")
+}
+
+fn main() {
+    let input = parse_input(&read_file(DAY));
+    println!("Part 1: {}", part1(&input));
+    println!("Part 2: {}", part2(&input));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use aoc2021::*;
+
+    const TEST_INPUT: &str = "6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5";
+
+    test!(part1() == 17);
+    // test!(part2() == 0);
+    bench!(part1() == 661);
+    // bench!(part2() == 0);
+    bench_input!(input_len_for_bench => 1323);
+
+    #[bench]
+    fn bench_part2(b: &mut test::Bencher) {
+        let parsed = parse_input(&read_file(DAY));
+        b.iter(|| assert_eq!(part2(&parsed).len(), 279));
+    }
+
+    fn input_len_for_bench((grid, folds): &Parsed) -> usize {
+        grid.len() + folds.len()
+    }
+}