diff --git a/package-lock.json b/package-lock.json
index 36f478588..07eac317f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -43,6 +43,7 @@
         "@eslint/compat": "^1.2.7",
         "@eslint/js": "^9.21.0",
         "@swc/jest": "^0.2.39",
+        "@total-typescript/ts-reset": "^0.6.1",
         "@types/benchmark": "^2.1.5",
         "@types/chai": "^4.3.17",
         "@types/d3": "^7.4.3",
@@ -6604,6 +6605,13 @@
         "@swc/counter": "^0.1.3"
       }
     },
+    "node_modules/@total-typescript/ts-reset": {
+      "version": "0.6.1",
+      "resolved": "https://registry.npmjs.org/@total-typescript/ts-reset/-/ts-reset-0.6.1.tgz",
+      "integrity": "sha512-cka47fVSo6lfQDIATYqb/vO1nvFfbPw7uWLayIXIhGETj0wcOOlrlkobOMDNQOFr9QOafegUPq13V2+6vtD7yg==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@tsconfig/node10": {
       "version": "1.0.11",
       "resolved": "https://registry.npmjs.org/@tsconfig/node10/-/node10-1.0.11.tgz",
diff --git a/package.json b/package.json
index fda1d731c..1b82703dd 100644
--- a/package.json
+++ b/package.json
@@ -31,6 +31,7 @@
     "@eslint/js": "^9.21.0",
     "@swc/jest": "^0.2.39",
     "@types/benchmark": "^2.1.5",
+    "@total-typescript/ts-reset": "^0.6.1",
     "@types/chai": "^4.3.17",
     "@types/d3": "^7.4.3",
     "@types/express": "^4.17.23",
diff --git a/src/client/ClientGameRunner.ts b/src/client/ClientGameRunner.ts
index 6d073fd30..eab9a3393 100644
--- a/src/client/ClientGameRunner.ts
+++ b/src/client/ClientGameRunner.ts
@@ -229,7 +229,7 @@ export class ClientGameRunner {
       players,
       // Not saving turns locally
       [],
-      startTime(),
+      startTime() ?? 0,
       Date.now(),
       update.winner,
       this.lobby.serverConfig,
diff --git a/src/client/Cosmetics.ts b/src/client/Cosmetics.ts
index bfd991c4a..ccd5a6d6d 100644
--- a/src/client/Cosmetics.ts
+++ b/src/client/Cosmetics.ts
@@ -1,4 +1,8 @@
-import { UserMeResponse } from "../core/ApiSchemas";
+import { z } from "zod";
+import {
+  StripeCreateCheckoutSessionResponseSchema,
+  UserMeResponse,
+} from "../core/ApiSchemas";
 import { Cosmetics, CosmeticsSchema, Pattern } from "../core/CosmeticSchemas";
 import { getApiBase, getAuthHeader } from "./jwt";
 
@@ -59,7 +63,15 @@ export async function handlePurchase(priceId: string) {
     return;
   }
 
-  const { url } = await response.json();
+  const json = await response.json();
+  const parsed = StripeCreateCheckoutSessionResponseSchema.safeParse(json);
+  if (!parsed.success) {
+    const error = z.prettifyError(parsed.error);
+    console.error("Invalid checkout session response:", error);
+    alert("Checkout failed. Please try again later.");
+    return;
+  }
+  const { url } = parsed.data;
 
   // Redirect to Stripe checkout
   window.location.href = url;
diff --git a/src/client/InputHandler.ts b/src/client/InputHandler.ts
index 15d6bee9d..5b9d397a8 100644
--- a/src/client/InputHandler.ts
+++ b/src/client/InputHandler.ts
@@ -159,7 +159,7 @@ export class InputHandler {
       groundAttack: "KeyG",
       modifierKey: "ControlLeft",
       altKey: "AltLeft",
-      ...JSON.parse(localStorage.getItem("settings.keybinds") ?? "{}"),
+      ...(JSON.parse(localStorage.getItem("settings.keybinds") ?? "{}") ?? {}),
     };
 
     // Mac users might have different keybinds
diff --git a/src/client/JoinPrivateLobbyModal.ts b/src/client/JoinPrivateLobbyModal.ts
index 1c875a7e7..8efd71156 100644
--- a/src/client/JoinPrivateLobbyModal.ts
+++ b/src/client/JoinPrivateLobbyModal.ts
@@ -1,8 +1,12 @@
 import { LitElement, html } from "lit";
 import { customElement, query, state } from "lit/decorators.js";
 import { translateText } from "../client/Utils";
-import { GameInfo, GameRecord } from "../core/Schemas";
+import { GameInfo } from "../core/Schemas";
 import { generateID } from "../core/Util";
+import {
+  WorkerApiArchivedGameLobbySchema,
+  WorkerApiGameIdExistsSchema,
+} from "../core/WorkerSchemas";
 import { getServerConfigFromClient } from "../core/configuration/ConfigLoader";
 import { JoinLobbyEvent } from "./Main";
 import "./components/baseComponents/Button";
@@ -198,7 +202,8 @@ export class JoinPrivateLobbyModal extends LitElement {
       headers: { "Content-Type": "application/json" },
     });
 
-    const gameInfo = await response.json();
+    const json = await response.json();
+    const gameInfo = WorkerApiGameIdExistsSchema.parse(json);
 
     if (gameInfo.exists) {
       this.message = translateText("private_lobby.joined_waiting");
@@ -231,7 +236,8 @@ export class JoinPrivateLobbyModal extends LitElement {
       headers: { "Content-Type": "application/json" },
     });
 
-    const archiveData = await archiveResponse.json();
+    const json = await archiveResponse.json();
+    const archiveData = WorkerApiArchivedGameLobbySchema.parse(json);
 
     if (
       archiveData.success === false &&
@@ -247,13 +253,11 @@ export class JoinPrivateLobbyModal extends LitElement {
     }
 
     if (archiveData.exists) {
-      const gameRecord = archiveData.gameRecord as GameRecord;
-
       this.dispatchEvent(
         new CustomEvent("join-lobby", {
           detail: {
             gameID: lobbyId,
-            gameRecord: gameRecord,
+            gameRecord: archiveData.gameRecord,
             clientID: generateID(),
           } as JoinLobbyEvent,
           bubbles: true,
diff --git a/src/client/LocalPersistantStats.ts b/src/client/LocalPersistantStats.ts
index c6dd1df5a..e08a2ff34 100644
--- a/src/client/LocalPersistantStats.ts
+++ b/src/client/LocalPersistantStats.ts
@@ -1,19 +1,34 @@
-import { GameConfig, GameID, GameRecord } from "../core/Schemas";
+import { z } from "zod";
+import {
+  GameConfig,
+  GameConfigSchema,
+  GameID,
+  GameRecord,
+  GameRecordSchema,
+  ID,
+} from "../core/Schemas";
 import { replacer } from "../core/Util";
 
-export interface LocalStatsData {
-  [key: GameID]: {
-    lobby: Partial<GameConfig>;
+const LocalStatsDataSchema = z.record(
+  ID,
+  z.object({
+    lobby: GameConfigSchema.partial(),
     // Only once the game is over
-    gameRecord?: GameRecord;
-  };
-}
+    gameRecord: GameRecordSchema.optional(),
+  }),
+);
+type LocalStatsData = z.infer<typeof LocalStatsDataSchema>;
 
-let _startTime: number;
+let _startTime: number | undefined;
 
 function getStats(): LocalStatsData {
-  const statsStr = localStorage.getItem("game-records");
-  return statsStr ? JSON.parse(statsStr) : {};
+  try {
+    return LocalStatsDataSchema.parse(
+      JSON.parse(localStorage.getItem("game-records") ?? "{}"),
+    );
+  } catch (e) {
+    return {};
+  }
 }
 
 function save(stats: LocalStatsData) {
diff --git a/src/client/MultiTabDetector.ts b/src/client/MultiTabDetector.ts
index 7b98965c6..90917c689 100644
--- a/src/client/MultiTabDetector.ts
+++ b/src/client/MultiTabDetector.ts
@@ -1,3 +1,10 @@
+import { z } from "zod";
+
+const LockSchema = z.object({
+  owner: z.string(),
+  timestamp: z.number(),
+});
+
 export class MultiTabDetector {
   private readonly tabId = `${Date.now()}-${Math.random()}`;
   private readonly lockKey = "multi-tab-lock";
@@ -60,7 +67,7 @@ export class MultiTabDetector {
     if (e.key === this.lockKey && e.newValue) {
       let other: { owner: string; timestamp: number };
       try {
-        other = JSON.parse(e.newValue);
+        other = LockSchema.parse(JSON.parse(e.newValue));
       } catch (e) {
         console.error("Failed to parse lock", e);
         return;
@@ -99,7 +106,7 @@ export class MultiTabDetector {
     const raw = localStorage.getItem(this.lockKey);
     if (!raw) return null;
     try {
-      return JSON.parse(raw);
+      return LockSchema.parse(JSON.parse(raw));
     } catch (e) {
       console.error("Failed to parse lock", raw, e);
       return null;
diff --git a/src/client/PublicLobby.ts b/src/client/PublicLobby.ts
index e94ed794b..512c63444 100644
--- a/src/client/PublicLobby.ts
+++ b/src/client/PublicLobby.ts
@@ -1,6 +1,7 @@
 import { LitElement, html } from "lit";
 import { customElement, state } from "lit/decorators.js";
 import { translateText } from "../client/Utils";
+import { ApiPublicLobbiesResponseSchema } from "../core/ExpressSchemas";
 import { GameMapType, GameMode } from "../core/game/Game";
 import { GameID, GameInfo } from "../core/Schemas";
 import { generateID } from "../core/Util";
@@ -77,7 +78,8 @@ export class PublicLobby extends LitElement {
       const response = await fetch(`/api/public_lobbies`);
       if (!response.ok)
         throw new Error(`HTTP error! status: ${response.status}`);
-      const data = await response.json();
+      const json = await response.json();
+      const data = ApiPublicLobbiesResponseSchema.parse(json);
       return data.lobbies;
     } catch (error) {
       console.error("Error fetching lobbies:", error);
diff --git a/src/client/UserSettingModal.ts b/src/client/UserSettingModal.ts
index d55f644ea..90e3b2e07 100644
--- a/src/client/UserSettingModal.ts
+++ b/src/client/UserSettingModal.ts
@@ -1,5 +1,6 @@
 import { LitElement, html } from "lit";
 import { customElement, query, state } from "lit/decorators.js";
+import { z } from "zod";
 import { translateText } from "../client/Utils";
 import { UserSettings } from "../core/game/UserSettings";
 import "./components/baseComponents/setting/SettingKeybind";
@@ -8,6 +9,8 @@ import "./components/baseComponents/setting/SettingNumber";
 import "./components/baseComponents/setting/SettingSlider";
 import "./components/baseComponents/setting/SettingToggle";
 
+const KeybindSchema = z.record(z.string(), z.string());
+
 @customElement("user-setting")
 export class UserSettingModal extends LitElement {
   private userSettings: UserSettings = new UserSettings();
@@ -25,7 +28,7 @@ export class UserSettingModal extends LitElement {
     const savedKeybinds = localStorage.getItem("settings.keybinds");
     if (savedKeybinds) {
       try {
-        this.keybinds = JSON.parse(savedKeybinds);
+        this.keybinds = KeybindSchema.parse(JSON.parse(savedKeybinds));
       } catch (e) {
         console.warn("Invalid keybinds JSON:", e);
       }
diff --git a/src/core/ApiSchemas.ts b/src/core/ApiSchemas.ts
index e4d3f74fa..493fab6f4 100644
--- a/src/core/ApiSchemas.ts
+++ b/src/core/ApiSchemas.ts
@@ -1,3 +1,4 @@
+// This file contains schemas for api.openfront.io
 import { z } from "zod";
 import { base64urlToUuid } from "./Base64";
 
@@ -48,3 +49,19 @@ export const UserMeResponseSchema = z.object({
   }),
 });
 export type UserMeResponse = z.infer<typeof UserMeResponseSchema>;
+
+export const StripeCreateCheckoutSessionResponseSchema = z.object({
+  id: z.string(),
+  object: z.literal("checkout.session"),
+  url: z.string(),
+  payment_status: z.enum(["paid", "unpaid", "no_payment_required"]),
+  status: z.enum(["open", "complete", "expired"]),
+  client_reference_id: z.string().optional(),
+  customer: z.string().optional(),
+  payment_intent: z.string().optional(),
+  subscription: z.string().optional(),
+  metadata: z.partialRecord(z.string(), z.string()),
+});
+export type StripeCreateCheckoutSessionResponse = z.infer<
+  typeof StripeCreateCheckoutSessionResponseSchema
+>;
diff --git a/src/core/CosmeticSchemas.ts b/src/core/CosmeticSchemas.ts
index f2855ab18..c7860c3cf 100644
--- a/src/core/CosmeticSchemas.ts
+++ b/src/core/CosmeticSchemas.ts
@@ -1,4 +1,4 @@
-import { z } from "zod/v4";
+import { z } from "zod";
 import { RequiredPatternSchema } from "./Schemas";
 
 export const ProductSchema = z.object({
diff --git a/src/core/ExpressSchemas.ts b/src/core/ExpressSchemas.ts
new file mode 100644
index 000000000..fbbc6fb90
--- /dev/null
+++ b/src/core/ExpressSchemas.ts
@@ -0,0 +1,15 @@
+// This file contians schemas for the primary openfront express server
+import { z } from "zod";
+import { GameInfoSchema } from "./Schemas";
+
+export const ApiEnvResponseSchema = z.object({
+  game_env: z.string(),
+});
+export type ApiEnvResponse = z.infer<typeof ApiEnvResponseSchema>;
+
+export const ApiPublicLobbiesResponseSchema = z.object({
+  lobbies: GameInfoSchema.array(),
+});
+export type ApiPublicLobbiesResponse = z.infer<
+  typeof ApiPublicLobbiesResponseSchema
+>;
diff --git a/src/core/Schemas.ts b/src/core/Schemas.ts
index e96d0c17d..f46a535ba 100644
--- a/src/core/Schemas.ts
+++ b/src/core/Schemas.ts
@@ -112,17 +112,6 @@ export type Player = z.infer<typeof PlayerSchema>;
 export type GameStartInfo = z.infer<typeof GameStartInfoSchema>;
 const PlayerTypeSchema = z.enum(PlayerType);
 
-export interface GameInfo {
-  gameID: GameID;
-  clients?: ClientInfo[];
-  numClients?: number;
-  msUntilStart?: number;
-  gameConfig?: GameConfig;
-}
-export interface ClientInfo {
-  clientID: ClientID;
-  username: string;
-}
 export enum LogSeverity {
   Debug = "DEBUG",
   Info = "INFO",
@@ -192,6 +181,22 @@ export const ID = z
 export const AllPlayersStatsSchema = z.record(ID, PlayerStatsSchema);
 
 export const UsernameSchema = SafeString;
+
+export const ClientInfoSchema = z.object({
+  clientID: ID,
+  username: UsernameSchema,
+});
+export type ClientInfo = z.infer<typeof ClientInfoSchema>;
+
+export const GameInfoSchema = z.object({
+  clients: ClientInfoSchema.array().optional(),
+  gameConfig: GameConfigSchema.optional(),
+  gameID: ID,
+  msUntilStart: z.number().int().nonnegative().optional(),
+  numClients: z.number().int().nonnegative().optional(),
+});
+export type GameInfo = z.infer<typeof GameInfoSchema>;
+
 const countryCodes = countries.map((c) => c.code);
 export const FlagSchema = z
   .string()
diff --git a/src/core/WorkerSchemas.ts b/src/core/WorkerSchemas.ts
index 0a06b1571..dbda38b10 100644
--- a/src/core/WorkerSchemas.ts
+++ b/src/core/WorkerSchemas.ts
@@ -1,5 +1,6 @@
+// This file contians schemas for the openfront worker express server
 import { z } from "zod";
-import { GameConfigSchema } from "./Schemas";
+import { GameConfigSchema, GameRecordSchema } from "./Schemas";
 
 export const CreateGameInputSchema = GameConfigSchema.or(
   z
@@ -9,3 +10,33 @@ export const CreateGameInputSchema = GameConfigSchema.or(
 );
 
 export const GameInputSchema = GameConfigSchema.partial();
+
+export const WorkerApiGameIdExistsSchema = z.object({
+  exists: z.boolean(),
+});
+export type WorkerApiGameIdExists = z.infer<typeof WorkerApiGameIdExistsSchema>;
+
+export const WorkerApiArchivedGameLobbySchema = z.union([
+  z.object({
+    error: z.literal("Game not found"),
+    exists: z.literal(false),
+    success: z.literal(false),
+  }),
+  z.object({
+    details: z.object({
+      actualCommit: z.string(),
+      expectedCommit: z.string(),
+    }),
+    error: z.literal("Version mismatch"),
+    exists: z.literal(true),
+    success: z.literal(false),
+  }),
+  z.object({
+    exists: z.literal(true),
+    gameRecord: GameRecordSchema,
+    success: z.literal(true),
+  }),
+]);
+export type WorkerApiArchivedGameLobby = z.infer<
+  typeof WorkerApiArchivedGameLobbySchema
+>;
diff --git a/src/core/configuration/ConfigLoader.ts b/src/core/configuration/ConfigLoader.ts
index 184902694..7fd65c1d6 100644
--- a/src/core/configuration/ConfigLoader.ts
+++ b/src/core/configuration/ConfigLoader.ts
@@ -1,3 +1,4 @@
+import { ApiEnvResponseSchema } from "../ExpressSchemas";
 import { UserSettings } from "../game/UserSettings";
 import { GameConfig } from "../Schemas";
 import { Config, GameEnv, ServerConfig } from "./Config";
@@ -36,7 +37,8 @@ export async function getServerConfigFromClient(): Promise<ServerConfig> {
       `Failed to fetch server config: ${response.status} ${response.statusText}`,
     );
   }
-  const config = await response.json();
+  const json = await response.json();
+  const config = ApiEnvResponseSchema.parse(json);
   // Log the retrieved configuration
   console.log("Server config loaded:", config);
 
diff --git a/src/core/game/FetchGameMapLoader.ts b/src/core/game/FetchGameMapLoader.ts
index 8e218b706..c9692983d 100644
--- a/src/core/game/FetchGameMapLoader.ts
+++ b/src/core/game/FetchGameMapLoader.ts
@@ -1,5 +1,6 @@
 import { GameMapType } from "./Game";
 import { GameMapLoader, MapData } from "./GameMapLoader";
+import { MapManifestSchema } from "./TerrainMapLoader";
 
 export class FetchGameMapLoader implements GameMapLoader {
   private maps: Map<GameMapType, MapData>;
@@ -66,6 +67,6 @@ export class FetchGameMapLoader implements GameMapLoader {
       throw new Error(`Failed to load ${url}: ${response.statusText}`);
     }
 
-    return response.json();
+    return response.json().then(MapManifestSchema.parse);
   }
 }
diff --git a/src/core/game/TerrainMapLoader.ts b/src/core/game/TerrainMapLoader.ts
index f59799b38..588b8b98b 100644
--- a/src/core/game/TerrainMapLoader.ts
+++ b/src/core/game/TerrainMapLoader.ts
@@ -1,3 +1,4 @@
+import { z } from "zod";
 import { GameMapType } from "./Game";
 import { GameMap, GameMapImpl } from "./GameMap";
 import { GameMapLoader } from "./GameMapLoader";
@@ -10,25 +11,28 @@ export type TerrainMapData = {
 
 const loadedMaps = new Map<GameMapType, TerrainMapData>();
 
-export interface MapMetadata {
-  width: number;
-  height: number;
-  num_land_tiles: number;
-}
+export const MapMetadataSchema = z.object({
+  height: z.number(),
+  num_land_tiles: z.number(),
+  width: z.number(),
+});
+export type MapMetadata = z.infer<typeof MapMetadataSchema>;
 
-export interface MapManifest {
-  name: string;
-  map: MapMetadata;
-  mini_map: MapMetadata;
-  nations: Nation[];
-}
+export const NationSchema = z.object({
+  coordinates: z.tuple([z.number(), z.number()]),
+  flag: z.string(),
+  name: z.string(),
+  strength: z.number(),
+});
+export type Nation = z.infer<typeof NationSchema>;
 
-export interface Nation {
-  coordinates: [number, number];
-  flag: string;
-  name: string;
-  strength: number;
-}
+export const MapManifestSchema = z.object({
+  map: MapMetadataSchema,
+  mini_map: MapMetadataSchema,
+  name: z.string(),
+  nations: NationSchema.array(),
+});
+export type MapManifest = z.infer<typeof MapManifestSchema>;
 
 export async function loadTerrainMap(
   map: GameMapType,
diff --git a/src/core/game/UnitGrid.ts b/src/core/game/UnitGrid.ts
index a60fadf53..f17ce3e1e 100644
--- a/src/core/game/UnitGrid.ts
+++ b/src/core/game/UnitGrid.ts
@@ -144,7 +144,12 @@ export class UnitGrid {
       searchRange,
     );
     const rangeSquared = searchRange * searchRange;
-    const typeSet = Array.isArray(types) ? new Set(types) : new Set([types]);
+    const typeSet = new Set(
+      // Using typeof check instead of Array.isArray due to a typescript
+      // narrowing limitation. For more information, see the full issue
+      // discussion at https://github.com/mattpocock/ts-reset/issues/48
+      typeof types === "object" ? types : [types],
+    );
     for (let cy = startGridY; cy <= endGridY; cy++) {
       for (let cx = startGridX; cx <= endGridX; cx++) {
         for (const type of typeSet) {
diff --git a/src/reset.d.ts b/src/reset.d.ts
new file mode 100644
index 000000000..a3d4a031b
--- /dev/null
+++ b/src/reset.d.ts
@@ -0,0 +1 @@
+import "@total-typescript/ts-reset";
diff --git a/src/server/Cloudflare.ts b/src/server/Cloudflare.ts
index eef337974..140e868f6 100644
--- a/src/server/Cloudflare.ts
+++ b/src/server/Cloudflare.ts
@@ -1,6 +1,7 @@
 import { spawn } from "child_process";
 import { promises as fs } from "fs";
 import yaml from "js-yaml";
+import { z } from "zod";
 import { logger } from "./Logger";
 
 const log = logger.child({
@@ -41,6 +42,12 @@ interface CloudflaredConfig {
   }>;
 }
 
+const CloudflareTunnelConfigSchema = z.object({
+  a: z.string(),
+  s: z.string(),
+  t: z.string(),
+});
+
 export class Cloudflare {
   private baseUrl = "https://api.cloudflare.com/client/v4";
 
@@ -157,14 +164,12 @@ export class Cloudflare {
     tunnelName: string,
   ): Promise<void> {
     log.info(`Creating local config for tunnel ${subdomain}.${domain}...`);
-    const tokenData = JSON.parse(
-      Buffer.from(tunnelToken, "base64").toString("utf8"),
+    const tokenData = CloudflareTunnelConfigSchema.parse(
+      JSON.parse(Buffer.from(tunnelToken, "base64").toString("utf8")),
     );
 
     const credentials = {
-      // eslint-disable-next-line @typescript-eslint/prefer-nullish-coalescing
       AccountTag: tokenData.a || this.accountId,
-      // eslint-disable-next-line @typescript-eslint/prefer-nullish-coalescing
       TunnelID: tokenData.t || tunnelId,
       TunnelName: tunnelName,
       TunnelSecret: tokenData.s,
diff --git a/src/server/Master.ts b/src/server/Master.ts
index ff693c323..e5d0f6688 100644
--- a/src/server/Master.ts
+++ b/src/server/Master.ts
@@ -5,6 +5,10 @@ import http from "http";
 import path from "path";
 import { fileURLToPath } from "url";
 import { getServerConfigFromServer } from "../core/configuration/ConfigLoader";
+import {
+  ApiEnvResponse,
+  ApiPublicLobbiesResponse,
+} from "../core/ExpressSchemas";
 import { GameInfo, ID } from "../core/Schemas";
 import { generateID } from "../core/Util";
 import { gatekeeper, LimiterType } from "./Gatekeeper";
@@ -59,7 +63,9 @@ app.use(
   }),
 );
 
-let publicLobbiesJsonStr = "";
+let publicLobbiesJsonStr = JSON.stringify({
+  lobbies: [],
+} satisfies ApiPublicLobbiesResponse);
 
 const publicLobbyIDs: Set<string> = new Set();
 
@@ -145,8 +151,8 @@ export async function startMaster() {
 app.get(
   "/api/env",
   gatekeeper.httpHandler(LimiterType.Get, async (req, res) => {
-    const envConfig = {
-      game_env: process.env.GAME_ENV,
+    const envConfig: ApiEnvResponse = {
+      game_env: process.env.GAME_ENV ?? "",
     };
     if (!envConfig.game_env) return res.sendStatus(500);
     res.json(envConfig);
@@ -266,7 +272,7 @@ async function fetchLobbies(): Promise<number> {
   // Update the JSON string
   publicLobbiesJsonStr = JSON.stringify({
     lobbies: lobbyInfos,
-  });
+  } satisfies ApiPublicLobbiesResponse);
 
   return publicLobbyIDs.size;
 }
diff --git a/src/server/Worker.ts b/src/server/Worker.ts
index 9f4bccfbc..a0ef684c1 100644
--- a/src/server/Worker.ts
+++ b/src/server/Worker.ts
@@ -10,7 +10,11 @@ import { GameEnv } from "../core/configuration/Config";
 import { getServerConfigFromServer } from "../core/configuration/ConfigLoader";
 import { GameType } from "../core/game/Game";
 import { GameRecord, GameRecordSchema, ID } from "../core/Schemas";
-import { CreateGameInputSchema, GameInputSchema } from "../core/WorkerSchemas";
+import {
+  CreateGameInputSchema,
+  GameInputSchema,
+  WorkerApiGameIdExists,
+} from "../core/WorkerSchemas";
 import { archive, readGameRecord } from "./Archive";
 import { GameManager } from "./GameManager";
 import { gatekeeper, LimiterType } from "./Gatekeeper";
@@ -201,7 +205,7 @@ export async function startWorker() {
       const lobbyId = req.params.id;
       res.json({
         exists: gm.game(lobbyId) !== null,
-      });
+      } satisfies WorkerApiGameIdExists);
     }),
   );
 
diff --git a/tests/AutoUpgrade.test.ts b/tests/AutoUpgrade.test.ts
index 126929098..2d14933eb 100644
--- a/tests/AutoUpgrade.test.ts
+++ b/tests/AutoUpgrade.test.ts
@@ -147,9 +147,7 @@ describe("AutoUpgrade Feature", () => {
       const event = new AutoUpgradeEvent(100, 200);
       const eventString = JSON.stringify(event);
       const parsedEvent = JSON.parse(eventString);
-
-      expect(parsedEvent.x).toBe(100);
-      expect(parsedEvent.y).toBe(200);
+      expect(parsedEvent).toStrictEqual({ x: 100, y: 200 });
     });
   });
 });
diff --git a/tests/LangCode.test.ts b/tests/LangCode.test.ts
index fc4d4520b..d21695000 100644
--- a/tests/LangCode.test.ts
+++ b/tests/LangCode.test.ts
@@ -1,5 +1,6 @@
 import fs from "fs";
 import path from "path";
+import { z } from "zod";
 
 describe("LangCode Filename Check", () => {
   const langDir = path.join(__dirname, "../resources/lang");
@@ -14,9 +15,17 @@ describe("LangCode Filename Check", () => {
       return;
     }
 
+    const schema = z.object({
+      lang: z.object({
+        lang_code: z.string(),
+      }),
+    });
+
     for (const file of files) {
       const filePath = path.join(langDir, file);
-      const jsonData = JSON.parse(fs.readFileSync(filePath, "utf-8"));
+      const jsonData = schema.parse(
+        JSON.parse(fs.readFileSync(filePath, "utf-8")),
+      );
 
       const fileNameWithoutExt = path.basename(file, ".json");
       const langCode = jsonData.lang?.lang_code;
diff --git a/tests/LangSvg.test.ts b/tests/LangSvg.test.ts
index 3680e8441..07b54b763 100644
--- a/tests/LangSvg.test.ts
+++ b/tests/LangSvg.test.ts
@@ -21,7 +21,14 @@ describe("Lang SVG Field and File Existence Check", () => {
       try {
         const filePath = path.join(langDir, file);
         const jsonData = JSON.parse(fs.readFileSync(filePath, "utf-8"));
-        const langSvg = jsonData.lang?.svg;
+        const langSvg =
+          jsonData &&
+          typeof jsonData === "object" &&
+          "lang" in jsonData &&
+          jsonData.lang &&
+          typeof jsonData.lang === "object" &&
+          "svg" in jsonData.lang &&
+          jsonData.lang.svg;
         if (typeof langSvg !== "string" || langSvg.length === 0) {
           errors.push(
             `[${file}]: lang.svg is missing or not a non-empty string`,
diff --git a/tests/testdata/maps/big_plains/manifest.json b/tests/testdata/maps/big_plains/manifest.json
index 3d3f9f3e2..8b2908a4a 100644
--- a/tests/testdata/maps/big_plains/manifest.json
+++ b/tests/testdata/maps/big_plains/manifest.json
@@ -9,5 +9,6 @@
     "num_land_tiles": 10000,
     "width": 100
   },
+  "nations": [],
   "name": "Big Plains"
 }
diff --git a/tests/testdata/maps/half_land_half_ocean/manifest.json b/tests/testdata/maps/half_land_half_ocean/manifest.json
index d28f3fdda..ec13acbe7 100644
--- a/tests/testdata/maps/half_land_half_ocean/manifest.json
+++ b/tests/testdata/maps/half_land_half_ocean/manifest.json
@@ -9,5 +9,6 @@
     "num_land_tiles": 48,
     "width": 8
   },
+  "nations": [],
   "name": "Half Land Half Ocean"
 }
diff --git a/tests/testdata/maps/ocean_and_land/manifest.json b/tests/testdata/maps/ocean_and_land/manifest.json
index c8bacdc39..7d94ba50e 100644
--- a/tests/testdata/maps/ocean_and_land/manifest.json
+++ b/tests/testdata/maps/ocean_and_land/manifest.json
@@ -9,5 +9,6 @@
     "num_land_tiles": 50,
     "width": 8
   },
+  "nations": [],
   "name": "Ocean and Land"
 }
diff --git a/tests/testdata/maps/plains/manifest.json b/tests/testdata/maps/plains/manifest.json
index 3b013ee24..852de2478 100644
--- a/tests/testdata/maps/plains/manifest.json
+++ b/tests/testdata/maps/plains/manifest.json
@@ -9,5 +9,6 @@
     "num_land_tiles": 2500,
     "width": 50
   },
+  "nations": [],
   "name": "Plains"
 }
diff --git a/tests/util/Setup.ts b/tests/util/Setup.ts
index 3253eb9a8..bae083f6f 100644
--- a/tests/util/Setup.ts
+++ b/tests/util/Setup.ts
@@ -1,5 +1,6 @@
 import fs from "fs";
 import path from "path";
+import { z } from "zod";
 import {
   Difficulty,
   Game,
@@ -12,7 +13,7 @@ import {
 import { createGame } from "../../src/core/game/GameImpl";
 import {
   genTerrainFromBin,
-  MapManifest,
+  MapManifestSchema,
 } from "../../src/core/game/TerrainMapLoader";
 import { UserSettings } from "../../src/core/game/UserSettings";
 import { GameConfig } from "../../src/core/Schemas";
@@ -44,9 +45,14 @@ export async function setup(
 
   const mapBinBuffer = fs.readFileSync(mapBinPath);
   const miniMapBinBuffer = fs.readFileSync(miniMapBinPath);
-  const manifest = JSON.parse(
-    fs.readFileSync(manifestPath, "utf8"),
-  ) satisfies MapManifest;
+  const str = fs.readFileSync(manifestPath, "utf8");
+  const raw = JSON.parse(str);
+  const parsed = MapManifestSchema.safeParse(raw);
+  if (!parsed.success) {
+    const error = z.prettifyError(parsed.error);
+    throw new Error(`Error parsing ${manifestPath}: ${error}`);
+  }
+  const manifest = parsed.data;
 
   const gameMap = await genTerrainFromBin(manifest.map, mapBinBuffer);
   const miniGameMap = await genTerrainFromBin(