diff --git a/2021/13/part1.mjs b/2021/13/part1.mjs
new file mode 100644
index 0000000..74fa80c
--- /dev/null
+++ b/2021/13/part1.mjs
@@ -0,0 +1,70 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+export const processInput = (input) => fs.readFile(input,'utf8').then(
+    content => {
+        let [ coords, instructions ] = content.split("\n\n");
+
+        let grid = [];
+
+        for( const [y,x] of coords.split("\n").map(line => line.split(",").map( x => parseInt(x) )) ) {
+            if(!grid[x]) grid[x] = [];
+            grid[x][y] = true;
+        }
+
+        grid = [...grid];
+        grid = grid.map( x => x? [...x]:[] );
+
+        instructions = instructions.split("\n").filter(x=>x).map( line => line.match(/([xy])=(\d+)/) )
+        .map( ([_,direction,level]) => ([direction,parseInt(level)]) );
+
+        return {
+            grid,
+            instructions,
+        }
+
+    }
+);
+
+export function foldGrid(grid,direction,level) {
+    if(direction === 'x') {
+        for( const row of grid ) {
+            if(!row) continue;
+            const folded = row.splice(level);
+            folded.forEach((v,i) => {
+                if(i===0) return;
+                if(!v) return;
+                row[level-i] = v;
+            })
+        }
+
+        return grid;
+    }
+
+    const folded = grid.splice(level);
+    folded.forEach((v,i) => {
+        if(i===0) return;
+        if(!v) return;
+        grid[level-i] =
+            _.range(_.max([grid[level-i].length,folded[i].length])).
+                map( j => grid[level-i][j] || folded[i][j] );
+    })
+
+    return grid;
+}
+
+export function printGrid(grid) {
+    return grid.map( line =>
+        (line||[]).map( x => x ? '#':'.' ).join('')
+     ).join("\n");
+}
+
+export function solution({grid, instructions}) {
+
+    foldGrid(grid,...instructions.shift());
+
+    return _.sum(grid.flat());
+
+
+}
diff --git a/2021/13/part2.mjs b/2021/13/part2.mjs
new file mode 100644
index 0000000..afdbfa6
--- /dev/null
+++ b/2021/13/part2.mjs
@@ -0,0 +1,14 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+import * as p1 from './part1.mjs';
+
+export function solution({grid, instructions}) {
+
+    instructions.forEach(i =>p1.foldGrid(grid,...i));
+
+    return p1.printGrid(grid);
+
+
+}
diff --git a/2021/13/sample b/2021/13/sample
new file mode 100644
index 0000000..282114c
--- /dev/null
+++ b/2021/13/sample
@@ -0,0 +1,21 @@
+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
diff --git a/2021/13/test.mjs b/2021/13/test.mjs
new file mode 100644
index 0000000..63f3239
--- /dev/null
+++ b/2021/13/test.mjs
@@ -0,0 +1,28 @@
+// https://adventofcode.com/2021/day/13
+
+import tap from "tap";
+import fs from "fs-extra";
+
+import * as p1 from "./part1.mjs";
+import * as p2 from "./part2.mjs";
+
+const sample = p1.processInput('sample');
+const input = p1.processInput('input');
+
+tap.test("part1", async (t) => {
+    const x = await sample;
+    t.equal(p1.solution(x), 17);
+    t.equal(p1.solution(x), 16);
+    t.equal(p1.solution(await input), 745);
+});
+
+tap.test("part2", async (t) => {
+    // t.equal(p2.solution(await sample), 0);
+    t.equal(p2.solution(await input),
+        `.##..###..#..#...##.####.###...##...##..
+#..#.#..#.#.#.....#.#....#..#.#..#.#..#.
+#..#.###..##......#.###..###..#....#....
+####.#..#.#.#.....#.#....#..#.#.##.#....
+#..#.#..#.#.#..#..#.#....#..#.#..#.#..#.
+#..#.###..#..#..##..#....###...###..##..`);
+});