diff --git a/src/lib/serial/chord.spec.ts b/src/lib/serial/chord.spec.ts
index a951b7c3..952d5303 100644
--- a/src/lib/serial/chord.spec.ts
+++ b/src/lib/serial/chord.spec.ts
@@ -1,8 +1,56 @@
 import {describe, it, expect} from "vitest"
-import {serializeActions} from "$lib/serial/chord"
+import {
+  chordAsCommandCompatible,
+  chordFromCommandCompatible,
+  chordsFromFile,
+  chordsToFile,
+  deserializeActions,
+  serializeActions,
+} from "./chord"
+import type {Chord} from "./chord"
 
 describe("chords", function () {
-  it("should serialize actions", function () {
-    expect(serializeActions([67, 2])).toBe(0xcc200000000000000000000000000n)
+  describe("actions", function () {
+    it("should serialize actions", function () {
+      expect(serializeActions([32, 51]).toString(16)).toEqual(0xcc200000000000000000000000000n.toString(16))
+    })
+
+    it("should deserialize actions", function () {
+      expect(deserializeActions(0xcc200000000000000000000000000n)).toEqual([32, 51])
+    })
+
+    for (let i = 0; i < 12; i++) {
+      it(`should serialize back-forth ${i} actions`, function () {
+        const actions = Array.from({length: i}).map((_, i) => i + 1)
+        expect(deserializeActions(serializeActions(actions))).toEqual(actions)
+      })
+    }
+  })
+
+  describe("commands", function () {
+    it("should convert to a command", function () {
+      expect(chordAsCommandCompatible({actions: [32, 51], phrase: [0x01, 0x68, 0x72, 0xd4, 0x65]})).toEqual(
+        "000CC200000000000000000000000000 016872D465",
+      )
+    })
+
+    it("should parse a command", function () {
+      expect(chordFromCommandCompatible("000CC200000000000000000000000000 016872D465")).toEqual({
+        actions: [32, 51],
+        phrase: [0x01, 0x68, 0x72, 0xd4, 0x65],
+      })
+    })
+  })
+
+  describe("chl file format", function () {
+    const fileData: Chord[] = [
+      {phrase: [1, 2, 3, 4], actions: [5, 6, 7, 8, 9]},
+      {phrase: [10, 11], actions: [12, 13, 14, 15]},
+      {phrase: [16], actions: [17]},
+    ]
+
+    it("should should convert back-forth a file", function () {
+      expect(chordsFromFile(chordsToFile(fileData))).toEqual(fileData)
+    })
   })
 })
diff --git a/src/lib/serial/chord.ts b/src/lib/serial/chord.ts
index 1cce27df..81dce2c0 100644
--- a/src/lib/serial/chord.ts
+++ b/src/lib/serial/chord.ts
@@ -9,9 +9,9 @@ export interface Chord {
  * @example "000CC200000000000000000000000000 7468726565"
  */
 export function chordAsCommandCompatible(chord: Chord): string {
-  return `${serializeActions(chord.actions).toString(16).padStart(32)} ${chord.phrase.map(it =>
-    it.toString(16),
-  )}`
+  return `${serializeActions(chord.actions).toString(16).padStart(32, "0")} ${chord.phrase
+    .map(it => it.toString(16).padStart(2, "0"))
+    .join("")}`.toUpperCase()
 }
 
 /**
@@ -36,8 +36,8 @@ export function chordFromCommandCompatible(command: string): Chord {
  */
 export function serializeActions(actions: number[]): bigint {
   let native = 0n
-  for (let i = 0; i < actions.length; i++) {
-    native |= BigInt(actions[i] & 0x3ff) << BigInt((11 - i) * 10)
+  for (let i = 1; i <= actions.length; i++) {
+    native |= BigInt(actions[actions.length - i] & 0x3ff) << BigInt((12 - i) * 10)
   }
   return native
 }
@@ -91,7 +91,7 @@ export function chordsToFile(chords: Chord[]): ArrayBuffer {
   const view = new DataView(buffer)
   let byteOffset = 0
 
-  for (const byte of CHL_MAGIC) {
+  for (const byte of CHL_MAGIC.split("")) {
     view.setUint8(byteOffset++, byte.codePointAt(0)!)
   }
   view.setUint8(byteOffset++, CHL_VERSION)
@@ -99,7 +99,7 @@ export function chordsToFile(chords: Chord[]): ArrayBuffer {
   byteOffset += 4
   for (const chord of chords) {
     const actions = serializeActions(chord.actions)
-    view.setBigUint64(byteOffset, actions << 64n, true)
+    view.setBigUint64(byteOffset, actions >> 64n, true)
     byteOffset += 8
     view.setBigUint64(byteOffset, actions & 0xffff_ffff_ffff_ffffn, true)
     byteOffset += 8
@@ -121,17 +121,18 @@ export function chordsFromFile(buffer: ArrayBuffer): Chord[] {
   const view = new DataView(buffer)
   let byteOffset = 0
 
-  let magic = ""
+  const magic = []
   for (let i = 0; i < CHL_MAGIC.length; i++) {
-    magic += view.getUint8(byteOffset++)
+    magic.push(view.getUint8(byteOffset++))
   }
-  if (magic !== CHL_MAGIC) throw new Error("Not a .chl file")
+  const magicString = String.fromCodePoint(...magic)
+  if (magicString !== CHL_MAGIC) throw new Error(`Not a .chl file [magic ${magicString}]`)
   if (view.getUint8(byteOffset++) !== CHL_VERSION) throw Error("Invalid .chl [version]")
 
   const chords: Chord[] = Array.from({length: view.getUint32(byteOffset, true)})
   byteOffset += 4
   for (let i = 0; i < chords.length; i++) {
-    let actions = view.getBigUint64(byteOffset, true) >> 64n
+    let actions = view.getBigUint64(byteOffset, true) << 64n
     byteOffset += 8
     actions |= view.getBigUint64(byteOffset, true)
     byteOffset += 8