diff --git a/src/save.ts b/src/save.ts
index c147759..a0e80d8 100644
--- a/src/save.ts
+++ b/src/save.ts
@@ -1,7 +1,7 @@
 import { getPlayerProgress } from "./playerprogress";
 import { getStateManager } from "./statemanager";
 import { getThralls } from "./thralls";
-import { SaveFileV1, StatCounterV1 } from "./saveformat";
+import { SaveFileV1, mustBeSaveFileV1 } from "./saveformat";
 
 export interface SaveFile {
   version: string;
@@ -10,159 +10,6 @@ export interface SaveFile {
 
 type SaveSlot = "FLEDGLING_SLOT_1" | "FLEDGLING_SLOT_2";
 
-/// Checks whether obj is a valid save file, as far as we can tell, and returns
-/// it unchanged if it is, or throws an error if it's not valid.
-export function mustBeSaveFileV1(obj: unknown): SaveFileV1 {
-  if (obj === undefined || obj === null) {
-    throw new Error("nonexistent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`not an object; was ${typeof obj}`);
-  }
-
-  if (!("version" in obj)) {
-    throw new Error("no magic number");
-  }
-  if (obj.version !== "fledgling_save_v1") {
-    throw new Error(`bad magic number: ${obj.version}`);
-  }
-
-  return {
-    version: "fledgling_save_v1",
-    revision: mustGetNumber(obj, "revision"),
-    turn: mustGetNumber(obj, "turn"),
-    name: mustGetString(obj, "name"),
-    thrallTemplateId: mustGetNumber(obj, "thrallTemplateId"),
-    nImprovements: mustGetNumber(obj, "nImprovements"),
-    stats: mustGetStatCounterV1(obj, "stats"),
-    talents: mustGetStatCounterV1(obj, "talents"),
-    isInPenance: mustGetBoolean(obj, "isInPenance"),
-    wishId: mustGetNumber(obj, "wishId"),
-    exp: mustGetNumber(obj, "exp"),
-    blood: mustGetNumber(obj, "blood"),
-    itemsPurloined: mustGetNumber(obj, "itemsPurloined"),
-    skillsLearned: mustGetNumberArray(obj, "skillsLearned"),
-    untrimmedSkillsAvailableIds: mustGetNumberArray(
-      obj,
-      "untrimmedSkillsAvailableIds",
-    ),
-    thrallsUnlocked: mustGetNumberArray(obj, "thrallsUnlocked"),
-    thrallDamage: mustGetNumberArray(obj, "thrallDamage"),
-    thrallsObtainedItem: mustGetNumberArray(obj, "thrallsObtainedItem"),
-    thrallsDeliveredItem: mustGetNumberArray(obj, "thrallsDeliveredItem"),
-  };
-}
-
-function mustGetNumber(obj: object, key: string): number {
-  if (obj === null || obj === undefined) {
-    throw new Error("container absent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`container was not an object; was ${typeof obj}`);
-  }
-  if (!(key in obj)) {
-    throw new Error(`missing number: ${key}`);
-  }
-  const dict = obj as { [key: string]: any };
-  const val = dict[key];
-  if (typeof val !== "number") {
-    throw new Error(`not a number: ${key}: ${val}`);
-  }
-  return val;
-}
-
-function mustGetString(obj: object, key: string): string {
-  if (obj === null || obj === undefined) {
-    throw new Error("container absent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`container was not an object; was ${typeof obj}`);
-  }
-  if (!(key in obj)) {
-    throw new Error(`missing number: ${key}`);
-  }
-  const dict = obj as { [key: string]: any };
-  const val = dict[key];
-  if (typeof val !== "string") {
-    throw new Error(`not a string: ${key}: ${val}`);
-  }
-  return val;
-}
-
-function mustGetStatCounterV1(obj: object, key: string): StatCounterV1 {
-  if (obj === null || obj === undefined) {
-    throw new Error("container absent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`container was not an object; was ${typeof obj}`);
-  }
-  if (!(key in obj)) {
-    throw new Error(`missing number: ${key}`);
-  }
-  const dict = obj as { [key: string]: any };
-  const val = dict[key];
-  if (typeof val !== "object") {
-    throw new Error(`not an object: ${key}: ${val}`);
-  }
-
-  try {
-    return {
-      agi: mustGetNumber(val, "agi"),
-      int: mustGetNumber(val, "int"),
-      cha: mustGetNumber(val, "cha"),
-      psi: mustGetNumber(val, "psi"),
-    };
-  } catch (e) {
-    let message = "unrecognizable error";
-    if (e instanceof Error) {
-      message = e.message;
-    }
-    throw new Error(`reading ${key}: ${message}`);
-  }
-}
-
-function mustGetBoolean(obj: object, key: string): boolean {
-  if (obj === null || obj === undefined) {
-    throw new Error("container absent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`container was not an object; was ${typeof obj}`);
-  }
-  if (!(key in obj)) {
-    throw new Error(`missing number: ${key}`);
-  }
-  const dict = obj as { [key: string]: any };
-  const val = dict[key];
-  if (typeof val !== "boolean") {
-    throw new Error(`not boolean: ${key}: ${val}`);
-  }
-  return val;
-}
-
-function mustGetNumberArray(obj: object, key: string): number[] {
-  if (obj === null || obj === undefined) {
-    throw new Error("container absent");
-  }
-  if (typeof obj !== "object") {
-    throw new Error(`container was not an object; was ${typeof obj}`);
-  }
-  if (!(key in obj)) {
-    throw new Error(`missing number: ${key}`);
-  }
-  const dict = obj as { [key: string]: any };
-  const val = dict[key];
-  if (typeof val !== "object") {
-    throw new Error(`not an object: ${key}: ${val}`);
-  }
-
-  for (const x of val) {
-    if (typeof x !== "number") {
-      throw new Error(`contained non-number item in ${key}: ${val}`);
-    }
-  }
-  return val;
-}
-
 /// The result of attempting to load a V1 save file.
 interface SaveFileV1LoadResult {
   // If present and valid, the loaded file.