diff --git a/.eslintrc.js b/.eslintrc.js
index 54203c4ecb..a4870dd3da 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -42,4 +42,18 @@ module.exports = {
       version: "detect",
     },
   },
+  overrides: [
+    /**
+     * Some enums are subsets of other enums. For example, UniversityLocationName contains locations of 3 universities.
+     * With each member, we refer to the respective LocationName's member instead of using a literal string. This usage
+     * is okay, but it triggers the "prefer-literal-enum-member" rule. This rule is not useful in this case, so we
+     * suppress it in NetscriptDefinitions.d.ts.
+     */
+    {
+      files: ["src/ScriptEditor/NetscriptDefinitions.d.ts"],
+      rules: {
+        "@typescript-eslint/prefer-literal-enum-member": ["off"],
+      },
+    },
+  ],
 };
diff --git a/package-lock.json b/package-lock.json
index 0b365e1923..ea667f06c8 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -69,6 +69,7 @@
         "@types/react-beautiful-dnd": "^13.1.5",
         "@types/react-dom": "^17.0.21",
         "@types/react-resizable": "^3.0.5",
+        "@types/sprintf-js": "^1.1.4",
         "@typescript-eslint/eslint-plugin": "^6.9.1",
         "@typescript-eslint/parser": "^6.9.1",
         "babel-jest": "^29.7.0",
@@ -5124,6 +5125,13 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/sprintf-js": {
+      "version": "1.1.4",
+      "resolved": "https://registry.npmjs.org/@types/sprintf-js/-/sprintf-js-1.1.4.tgz",
+      "integrity": "sha512-aWK1reDYWxcjgcIIPmQi3u+OQDuYa9b+lr6eIsGWrekJ9vr1NSjr4Eab8oQ1iKuH1ltFHpXGyerAv1a3FMKxzQ==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/stack-utils": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/@types/stack-utils/-/stack-utils-2.0.1.tgz",
diff --git a/package.json b/package.json
index c0726b6e65..848c488664 100644
--- a/package.json
+++ b/package.json
@@ -70,6 +70,7 @@
     "@types/react-beautiful-dnd": "^13.1.5",
     "@types/react-dom": "^17.0.21",
     "@types/react-resizable": "^3.0.5",
+    "@types/sprintf-js": "^1.1.4",
     "@typescript-eslint/eslint-plugin": "^6.9.1",
     "@typescript-eslint/parser": "^6.9.1",
     "babel-jest": "^29.7.0",
diff --git a/src/Bladeburner/Bladeburner.ts b/src/Bladeburner/Bladeburner.ts
index 6d635f7150..f2bb03d841 100644
--- a/src/Bladeburner/Bladeburner.ts
+++ b/src/Bladeburner/Bladeburner.ts
@@ -51,6 +51,7 @@ import { Sleeve } from "../PersonObjects/Sleeve/Sleeve";
 import { autoCompleteTypeShorthand } from "./utils/terminalShorthands";
 import { resolveTeamCasualties, type OperationTeam } from "./Actions/TeamCasualties";
 import { shuffleArray } from "../Infiltration/ui/BribeGame";
+import { objectAssert } from "../utils/helpers/typeAssertion";
 
 export const BladeburnerPromise: PromisePair<number> = { promise: null, resolve: null };
 
@@ -1403,9 +1404,10 @@ export class Bladeburner implements OperationTeam {
 
   /** Initializes a Bladeburner object from a JSON save state. */
   static fromJSON(value: IReviverValue): Bladeburner {
+    objectAssert(value.data);
     // operations and contracts are not loaded directly from the save, we load them in using a different method
-    const contractsData = value.data?.contracts;
-    const operationsData = value.data?.operations;
+    const contractsData = value.data.contracts;
+    const operationsData = value.data.operations;
     const bladeburner = Generic_fromJSON(Bladeburner, value.data, Bladeburner.keysToLoad);
     // Loading this way allows better typesafety and also allows faithfully reconstructing contracts/operations
     // even from save data that is missing a lot of static info about the objects.
diff --git a/src/CodingContracts.ts b/src/CodingContracts.ts
index 6fe9c2bc6f..c0238be751 100644
--- a/src/CodingContracts.ts
+++ b/src/CodingContracts.ts
@@ -4,6 +4,7 @@ import { codingContractTypesMetadata } from "./data/codingcontracttypes";
 import { Generic_fromJSON, Generic_toJSON, IReviverValue, constructorsForReviver } from "./utils/JSONReviver";
 import { CodingContractEvent } from "./ui/React/CodingContractModal";
 import { ContractFilePath, resolveContractFilePath } from "./Paths/ContractFilePath";
+import { objectAssert } from "./utils/helpers/typeAssertion";
 
 /* Contract Types */
 export const CodingContractTypes = Object.fromEntries(codingContractTypesMetadata.map((x) => [x.name, x]));
@@ -127,6 +128,7 @@ export class CodingContract {
 
   /** Initializes a CodingContract from a JSON save state. */
   static fromJSON(value: IReviverValue): CodingContract {
+    objectAssert(value.data);
     // In previous versions, there was a data field instead of a state field.
     if ("data" in value.data) {
       value.data.state = value.data.data;
diff --git a/src/Corporation/CorporationState.ts b/src/Corporation/CorporationState.ts
index ae1705b8a3..8faf02ff47 100644
--- a/src/Corporation/CorporationState.ts
+++ b/src/Corporation/CorporationState.ts
@@ -1,6 +1,7 @@
 import { CorpStateName } from "@nsdefs";
 import { Generic_fromJSON, Generic_toJSON, IReviverValue, constructorsForReviver } from "../utils/JSONReviver";
 import { stateNames } from "./data/Constants";
+
 export class CorporationState {
   // Number representing what state the Corporation is in. The number
   // is an index for the array that holds all Corporation States
diff --git a/src/Gang/GangMember.ts b/src/Gang/GangMember.ts
index 80b6553462..1879f40b85 100644
--- a/src/Gang/GangMember.ts
+++ b/src/Gang/GangMember.ts
@@ -100,12 +100,6 @@ export class GangMember {
   }
 
   getTask(): GangMemberTask {
-    // TODO unplanned: transfer that to a save file migration function
-    // Backwards compatibility
-    if ((this.task as any) instanceof GangMemberTask) {
-      this.task = (this.task as any).name;
-    }
-
     if (Object.hasOwn(GangMemberTasks, this.task)) {
       return GangMemberTasks[this.task];
     }
diff --git a/src/Infiltration/ui/MinesweeperGame.tsx b/src/Infiltration/ui/MinesweeperGame.tsx
index 81df2942ee..be73738a46 100644
--- a/src/Infiltration/ui/MinesweeperGame.tsx
+++ b/src/Infiltration/ui/MinesweeperGame.tsx
@@ -165,9 +165,9 @@ function fieldEquals(a: boolean[][], b: boolean[][]): boolean {
 }
 
 function generateEmptyField(difficulty: Difficulty): boolean[][] {
-  const field = [];
+  const field: boolean[][] = [];
   for (let i = 0; i < Math.round(difficulty.height); i++) {
-    field.push(new Array(Math.round(difficulty.width)).fill(false));
+    field.push(new Array<boolean>(Math.round(difficulty.width)).fill(false));
   }
   return field;
 }
diff --git a/src/NetscriptFunctions.ts b/src/NetscriptFunctions.ts
index ecc4593bef..c1e55f4719 100644
--- a/src/NetscriptFunctions.ts
+++ b/src/NetscriptFunctions.ts
@@ -20,11 +20,12 @@ import {
   GymType,
   JobName,
   JobField,
-  LiteratureName,
+  type LiteratureName,
   LocationName,
   ToastVariant,
   UniversityClassType,
   CompanyName,
+  type MessageFilename,
 } from "@enums";
 import { PromptEvent } from "./ui/React/PromptManager";
 import { GetServer, DeleteServer, AddToAllServers, createUniqueRandomIp } from "./Server/AllServers";
@@ -145,8 +146,19 @@ export const ns: InternalAPI<NSFull> = {
   stock: NetscriptStockMarket(),
   grafting: NetscriptGrafting(),
   hacknet: NetscriptHacknet(),
-  sprintf: () => sprintf,
-  vsprintf: () => vsprintf,
+  sprintf:
+    (ctx) =>
+    (_format, ...args) => {
+      const format = helpers.string(ctx, "format", _format);
+      return sprintf(format, ...(args as unknown[]));
+    },
+  vsprintf: (ctx) => (_format, _args) => {
+    const format = helpers.string(ctx, "format", _format);
+    if (!Array.isArray(_args)) {
+      throw helpers.errorMessage(ctx, `args must be an array.`);
+    }
+    return vsprintf(format, _args);
+  },
   scan: (ctx) => (_hostname) => {
     const hostname = _hostname ? helpers.string(ctx, "hostname", _hostname) : ctx.workerScript.hostname;
     const server = helpers.getServer(ctx, hostname);
@@ -1163,7 +1175,8 @@ export const ns: InternalAPI<NSFull> = {
     if (!path) return false;
     if (hasScriptExtension(path)) return server.scripts.has(path);
     if (hasTextExtension(path)) return server.textFiles.has(path);
-    if (path.endsWith(".lit") || path.endsWith(".msg")) return server.messages.includes(path as any);
+    if (path.endsWith(".lit") || path.endsWith(".msg"))
+      return server.messages.includes(path as LiteratureName | MessageFilename);
     if (hasContractExtension(path)) return !!server.contracts.find(({ fn }) => fn === path);
     const lowerPath = path.toLowerCase();
     return server.programs.map((programName) => programName.toLowerCase()).includes(lowerPath);
diff --git a/src/NetscriptFunctions/Flags.ts b/src/NetscriptFunctions/Flags.ts
index 0e8a8075ba..15baa2aa64 100644
--- a/src/NetscriptFunctions/Flags.ts
+++ b/src/NetscriptFunctions/Flags.ts
@@ -3,6 +3,7 @@ import { toNative } from "./toNative";
 import libarg from "arg";
 import { NetscriptContext } from "../Netscript/APIWrapper";
 
+export type Schema = [string, string | number | boolean | string[]][];
 type FlagType = StringConstructor | NumberConstructor | BooleanConstructor | StringConstructor[];
 type FlagsRet = Record<string, ScriptArg | string[]>;
 export function Flags(ctx: NetscriptContext | string[]): (data: unknown) => FlagsRet {
@@ -12,7 +13,7 @@ export function Flags(ctx: NetscriptContext | string[]): (data: unknown) => Flag
     if (!Array.isArray(schema)) throw new Error("flags schema passed in is invalid.");
     const args: Record<string, FlagType> = {};
 
-    for (const d of schema) {
+    for (const d of schema as Schema) {
       let t: FlagType = String;
       if (typeof d[1] === "number") {
         t = Number;
@@ -24,13 +25,15 @@ export function Flags(ctx: NetscriptContext | string[]): (data: unknown) => Flag
       const numDashes = d[0].length > 1 ? 2 : 1;
       args["-".repeat(numDashes) + d[0]] = t;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-assignment
     const ret: FlagsRet = libarg(args, { argv: vargs });
-    for (const d of schema) {
+    for (const d of schema as Schema) {
       if (!Object.hasOwn(ret, "--" + d[0]) || !Object.hasOwn(ret, "-" + d[0])) ret[d[0]] = d[1];
     }
     for (const key of Object.keys(ret)) {
       if (!key.startsWith("-")) continue;
       const value = ret[key];
+      // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
       delete ret[key];
       const numDashes = key.length === 2 ? 1 : 2;
       ret[key.slice(numDashes)] = value;
diff --git a/src/NetscriptFunctions/UserInterface.ts b/src/NetscriptFunctions/UserInterface.ts
index 3d0577afa8..c387d5bd4f 100644
--- a/src/NetscriptFunctions/UserInterface.ts
+++ b/src/NetscriptFunctions/UserInterface.ts
@@ -82,14 +82,14 @@ export function NetscriptUserInterface(): InternalAPI<IUserInterface> {
     setStyles: (ctx) => (newStyles) => {
       const styleValidator: Record<string, string | number | undefined> = {};
       assertObjectType(ctx, "newStyles", newStyles, styleValidator);
-      const currentStyles = { ...Settings.styles };
+      const currentStyles: Record<string, unknown> = { ...Settings.styles };
       const errors: string[] = [];
       for (const key of Object.keys(newStyles)) {
-        if (!(currentStyles as any)[key]) {
+        if (!currentStyles[key]) {
           // Invalid key
           errors.push(`Invalid key "${key}"`);
         } else {
-          (currentStyles as any)[key] = newStyles[key];
+          currentStyles[key] = newStyles[key];
         }
       }
 
diff --git a/src/PersonObjects/Player/PlayerObject.ts b/src/PersonObjects/Player/PlayerObject.ts
index 818b714c0a..65ece9e95a 100644
--- a/src/PersonObjects/Player/PlayerObject.ts
+++ b/src/PersonObjects/Player/PlayerObject.ts
@@ -203,6 +203,7 @@ export class PlayerObject extends Person implements IPlayer {
     // Remove any invalid jobs
     for (const [loadedCompanyName, loadedJobName] of Object.entries(player.jobs)) {
       if (!isMember("CompanyName", loadedCompanyName) || !isMember("JobName", loadedJobName)) {
+        // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
         delete player.jobs[loadedCompanyName as CompanyName];
       }
     }
diff --git a/src/PersonObjects/Player/PlayerObjectGeneralMethods.ts b/src/PersonObjects/Player/PlayerObjectGeneralMethods.ts
index 50fd5ee717..3294efeaed 100644
--- a/src/PersonObjects/Player/PlayerObjectGeneralMethods.ts
+++ b/src/PersonObjects/Player/PlayerObjectGeneralMethods.ts
@@ -377,6 +377,7 @@ export function quitJob(this: PlayerObject, company: CompanyName, suppressDialog
       }
     }
   }
+  // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
   delete this.jobs[company];
 }
 
diff --git a/src/PersonObjects/Sleeve/Work/SleeveBladeburnerWork.ts b/src/PersonObjects/Sleeve/Work/SleeveBladeburnerWork.ts
index df86ba2409..355f5a6d47 100644
--- a/src/PersonObjects/Sleeve/Work/SleeveBladeburnerWork.ts
+++ b/src/PersonObjects/Sleeve/Work/SleeveBladeburnerWork.ts
@@ -10,6 +10,7 @@ import { scaleWorkStats } from "../../../Work/WorkStats";
 import { getKeyList } from "../../../utils/helpers/getKeyList";
 import { loadActionIdentifier } from "../../../Bladeburner/utils/loadActionIdentifier";
 import { invalidWork } from "../../../Work/InvalidWork";
+import { objectAssert } from "../../../utils/helpers/typeAssertion";
 
 interface SleeveBladeburnerWorkParams {
   actionId: ActionIdentifier & { type: BladeburnerActionType.General | BladeburnerActionType.Contract };
@@ -98,6 +99,7 @@ export class SleeveBladeburnerWork extends SleeveWorkClass {
 
   /** Initializes a BladeburnerWork object from a JSON save state. */
   static fromJSON(value: IReviverValue): SleeveBladeburnerWork {
+    objectAssert(value.data);
     const actionId = loadActionIdentifier(value.data?.actionId);
     if (!actionId) return invalidWork();
     value.data.actionId = actionId;
diff --git a/src/PersonObjects/Sleeve/Work/SleeveClassWork.ts b/src/PersonObjects/Sleeve/Work/SleeveClassWork.ts
index 91c4a9c780..896a9a6dd2 100644
--- a/src/PersonObjects/Sleeve/Work/SleeveClassWork.ts
+++ b/src/PersonObjects/Sleeve/Work/SleeveClassWork.ts
@@ -7,6 +7,7 @@ import { Sleeve } from "../Sleeve";
 import { scaleWorkStats, WorkStats } from "../../../Work/WorkStats";
 import { Locations } from "../../../Locations/Locations";
 import { isMember } from "../../../utils/EnumHelper";
+import { objectAssert } from "../../../utils/helpers/typeAssertion";
 
 export const isSleeveClassWork = (w: SleeveWorkClass | null): w is SleeveClassWork =>
   w !== null && w.type === SleeveWorkType.CLASS;
@@ -54,8 +55,13 @@ export class SleeveClassWork extends SleeveWorkClass {
 
   /** Initializes a ClassWork object from a JSON save state. */
   static fromJSON(value: IReviverValue): SleeveClassWork {
-    if (!(value.data.classType in Classes)) value.data.classType = "Computer Science";
-    if (!(value.data.location in Locations)) value.data.location = LocationName.Sector12RothmanUniversity;
+    objectAssert(value.data);
+    if (typeof value.data.classType !== "string" || !(value.data.classType in Classes)) {
+      value.data.classType = "Computer Science";
+    }
+    if (typeof value.data.location !== "string" || !(value.data.location in Locations)) {
+      value.data.location = LocationName.Sector12RothmanUniversity;
+    }
     return Generic_fromJSON(SleeveClassWork, value.data);
   }
 }
diff --git a/src/SaveObject.ts b/src/SaveObject.ts
index 98cb42b941..d5778cde81 100644
--- a/src/SaveObject.ts
+++ b/src/SaveObject.ts
@@ -225,7 +225,12 @@ class BitburnerSaveObject {
 
     let parsedSaveData;
     try {
-      parsedSaveData = JSON.parse(decodedSaveData);
+      parsedSaveData = JSON.parse(decodedSaveData) as {
+        ctor: string;
+        data: {
+          PlayerSave: string;
+        };
+      };
     } catch (error) {
       console.error(error); // We'll handle below
     }
@@ -632,6 +637,7 @@ function evaluateVersionCompatibility(ver: string | number): void {
     if (isNaN(intExp)) intExp = 0;
     anyPlayer.exp.intelligence += intExp;
     for (const field of removePlayerFields) {
+      // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
       delete anyPlayer[field];
     }
     for (const sleeve of anyPlayer.sleeves) {
@@ -640,6 +646,7 @@ function evaluateVersionCompatibility(ver: string | number): void {
       if (isNaN(intExp)) intExp = 0;
       anySleeve.exp.intelligence += intExp;
       for (const field of removeSleeveFields) {
+        // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
         delete sleeve[field];
       }
     }
diff --git a/src/ScriptEditor/ui/themes.ts b/src/ScriptEditor/ui/themes.ts
index 23152c2c8f..41fbebe816 100644
--- a/src/ScriptEditor/ui/themes.ts
+++ b/src/ScriptEditor/ui/themes.ts
@@ -79,7 +79,10 @@ export const sanitizeTheme = (theme: IScriptEditorTheme): void => {
     return;
   }
   for (const themeKey of getRecordKeys(theme)) {
-    if (typeof theme[themeKey] !== "object") delete theme[themeKey];
+    if (typeof theme[themeKey] !== "object") {
+      // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
+      delete theme[themeKey];
+    }
     switch (themeKey) {
       case "base":
         if (!["vs-dark", "vs"].includes(theme.base)) theme.base = "vs-dark";
diff --git a/src/Server/AllServers.ts b/src/Server/AllServers.ts
index 68bb36af10..2d3fd26d3f 100644
--- a/src/Server/AllServers.ts
+++ b/src/Server/AllServers.ts
@@ -13,6 +13,7 @@ import { currentNodeMults } from "../BitNode/BitNodeMultipliers";
 import { IPAddress, isIPAddress } from "../Types/strings";
 
 import "../Script/RunningScript"; // For reviver side-effect
+import { objectAssert } from "../utils/helpers/typeAssertion";
 
 /**
  * Map of all Servers that exist in the game
@@ -63,6 +64,7 @@ export function DeleteServer(serverkey: string): void {
   for (const key of Object.keys(AllServers)) {
     const server = AllServers[key];
     if (server.ip !== serverkey && server.hostname !== serverkey) continue;
+    // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
     delete AllServers[key];
     break;
   }
@@ -100,6 +102,7 @@ export function AddToAllServers(server: Server | HacknetServer): void {
 
 export const renameServer = (hostname: string, newName: string): void => {
   AllServers[newName] = AllServers[hostname];
+  // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
   delete AllServers[hostname];
 };
 
@@ -188,13 +191,22 @@ export function initForeignServers(homeComputer: Server): void {
 
 export function prestigeAllServers(): void {
   for (const member of Object.keys(AllServers)) {
+    // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
     delete AllServers[member];
   }
   AllServers = {};
 }
 
 export function loadAllServers(saveString: string): void {
-  AllServers = JSON.parse(saveString, Reviver);
+  const allServersData: unknown = JSON.parse(saveString, Reviver);
+  objectAssert(allServersData);
+  for (const [serverName, server] of Object.entries(allServersData)) {
+    if (!(server instanceof Server) && !(server instanceof HacknetServer)) {
+      throw new Error(`Server ${serverName} is not an instance of Server or HacknetServer.`);
+    }
+  }
+  // We validated the data above, so it's safe to typecast here.
+  AllServers = allServersData as typeof AllServers;
 }
 
 export function saveAllServers(): string {
diff --git a/src/Server/BaseServer.ts b/src/Server/BaseServer.ts
index 5c4564120a..1edb7b8577 100644
--- a/src/Server/BaseServer.ts
+++ b/src/Server/BaseServer.ts
@@ -24,6 +24,7 @@ import lodash from "lodash";
 import { Settings } from "../Settings/Settings";
 
 import type { ScriptKey } from "../utils/helpers/scriptKey";
+import { objectAssert } from "../utils/helpers/typeAssertion";
 
 interface IConstructorParams {
   adminRights?: boolean;
@@ -293,6 +294,7 @@ export abstract class BaseServer implements IServer {
     // RunningScripts are stored as a simple array, both for backward compatibility,
     // compactness, and ease of filtering them here.
     const result = Generic_toJSON(ctorName, this, keys);
+    objectAssert(result.data);
     if (Settings.ExcludeRunningScriptsFromSave) {
       result.data.runningScripts = [];
       return result;
@@ -313,8 +315,11 @@ export abstract class BaseServer implements IServer {
   // Initializes a Server Object from a JSON save state
   // Called by subclasses, not Reviver.
   static fromJSONBase<T extends BaseServer>(value: IReviverValue, ctor: new () => T, keys: readonly (keyof T)[]): T {
+    objectAssert(value.data);
     const server = Generic_fromJSON(ctor, value.data, keys);
-    server.savedScripts = value.data.runningScripts;
+    if (value.data.runningScripts != null && Array.isArray(value.data.runningScripts)) {
+      server.savedScripts = value.data.runningScripts;
+    }
     // If textFiles is not an array, we've already done the 2.3 migration to textFiles and scripts as maps + path changes.
     if (!Array.isArray(server.textFiles)) return server;
 
@@ -333,7 +338,7 @@ export abstract class BaseServer implements IServer {
     // In case somehow there are previously valid filenames that can't be sanitized, they will go in a new directory with a note.
     for (const script of oldScripts) {
       // We're about to do type validation on the filename anyway.
-      if (script.filename.endsWith(".ns")) script.filename = (script.filename + ".js") as any;
+      if (script.filename.endsWith(".ns")) script.filename = (script.filename + ".js") as ScriptFilePath;
       let newFilePath = resolveScriptFilePath(script.filename);
       if (!newFilePath) {
         newFilePath = `${newDirectory}script${++invalidScriptCount}.js` as ScriptFilePath;
diff --git a/src/StockMarket/StockMarket.tsx b/src/StockMarket/StockMarket.tsx
index f9ec466797..97018bb8d7 100644
--- a/src/StockMarket/StockMarket.tsx
+++ b/src/StockMarket/StockMarket.tsx
@@ -151,6 +151,7 @@ export function deleteStockMarket(): void {
 
 export function initStockMarket(): void {
   for (const stockName of Object.getOwnPropertyNames(StockMarket)) {
+    // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
     delete StockMarket[stockName];
   }
 
diff --git a/src/Terminal/commands/download.ts b/src/Terminal/commands/download.ts
index 946936c703..0258573f45 100644
--- a/src/Terminal/commands/download.ts
+++ b/src/Terminal/commands/download.ts
@@ -18,7 +18,7 @@ export function exportScripts(pattern: string, server: BaseServer, currDir = roo
   // Return an error if no files matched, rather than an empty zip folder
   if (Object.keys(zip.files).length == 0) throw new Error(`No files match the pattern ${pattern}`);
   const filename = `bitburner${
-    hasScriptExtension(pattern) ? "Scripts" : pattern.endsWith(".txt") ? "Texts" : "Files"
+    hasScriptExtension(pattern) ? "Scripts" : hasTextExtension(pattern) ? "Texts" : "Files"
   }.zip`;
   zip
     .generateAsync({ type: "blob" })
diff --git a/src/Terminal/commands/ls.tsx b/src/Terminal/commands/ls.tsx
index 7b2d9638fe..3159491ca2 100644
--- a/src/Terminal/commands/ls.tsx
+++ b/src/Terminal/commands/ls.tsx
@@ -33,6 +33,7 @@ export function ls(args: (string | number | boolean)[], server: BaseServer): voi
   }
   let flags: LSFlags;
   try {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-assignment
     flags = libarg(
       {
         "-l": Boolean,
diff --git a/src/Terminal/commands/ps.ts b/src/Terminal/commands/ps.ts
index 184a911e29..2606219184 100644
--- a/src/Terminal/commands/ps.ts
+++ b/src/Terminal/commands/ps.ts
@@ -4,8 +4,11 @@ import { matchScriptPathUnanchored } from "../../utils/helpers/scriptKey";
 import libarg from "arg";
 
 export function ps(args: (string | number | boolean)[], server: BaseServer): void {
-  let flags;
+  let flags: {
+    "--grep": string;
+  };
   try {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-assignment
     flags = libarg(
       {
         "--grep": String,
diff --git a/src/Terminal/commands/runScript.ts b/src/Terminal/commands/runScript.ts
index 5a24357b89..1f85f92f5b 100644
--- a/src/Terminal/commands/runScript.ts
+++ b/src/Terminal/commands/runScript.ts
@@ -18,8 +18,14 @@ export function runScript(path: ScriptFilePath, commandArgs: (string | number |
   if (!script) return Terminal.error(`Script ${path} does not exist on this server.`);
 
   const runArgs = { "--tail": Boolean, "-t": Number, "--ram-override": Number };
-  let flags;
+  let flags: {
+    _: ScriptArg[];
+    "--tail": boolean;
+    "-t": string;
+    "--ram-override": string;
+  };
   try {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-assignment
     flags = libarg(runArgs, {
       permissive: true,
       argv: commandArgs,
@@ -42,7 +48,7 @@ export function runScript(path: ScriptFilePath, commandArgs: (string | number |
   if (!server.hasAdminRights) return Terminal.error("Need root access to run script");
 
   // Todo: Switch out arg for something with typescript support
-  const args = flags._ as ScriptArg[];
+  const args = flags._;
 
   const singleRamUsage = ramOverride ?? script.getRamUsage(server.scripts);
   if (!singleRamUsage) {
diff --git a/src/Terminal/commands/tail.ts b/src/Terminal/commands/tail.ts
index b9e05c2938..9c68a54ec6 100644
--- a/src/Terminal/commands/tail.ts
+++ b/src/Terminal/commands/tail.ts
@@ -23,7 +23,10 @@ export function tail(commandArray: (string | number | boolean)[], server: BaseSe
       }
       // Just use the first one (if there are multiple with the same
       // arguments, they can't be distinguished except by pid).
-      LogBoxEvents.emit(candidates.values().next().value);
+      const next = candidates.values().next();
+      if (!next.done) {
+        LogBoxEvents.emit(next.value);
+      }
     } else if (typeof commandArray[0] === "number") {
       const runningScript = findRunningScriptByPid(commandArray[0]);
       if (runningScript == null) {
diff --git a/src/Terminal/getTabCompletionPossibilities.ts b/src/Terminal/getTabCompletionPossibilities.ts
index 6356ea036e..7c80f39f24 100644
--- a/src/Terminal/getTabCompletionPossibilities.ts
+++ b/src/Terminal/getTabCompletionPossibilities.ts
@@ -5,7 +5,7 @@ import { GetAllServers } from "../Server/AllServers";
 import { parseCommand, parseCommands } from "./Parser";
 import { HelpTexts } from "./HelpText";
 import { compile } from "../NetscriptJSEvaluator";
-import { Flags } from "../NetscriptFunctions/Flags";
+import { Flags, type Schema } from "../NetscriptFunctions/Flags";
 import { AutocompleteData } from "@nsdefs";
 import libarg from "arg";
 import { getAllDirectories, resolveDirectory, root } from "../Paths/Directory";
@@ -280,6 +280,7 @@ export async function getTabCompletionPossibilities(terminalText: string, baseDi
       _: [],
     };
     try {
+      // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-assignment
       flags = libarg(runArgs, {
         permissive: true,
         argv: command.slice(2),
@@ -299,9 +300,9 @@ export async function getTabCompletionPossibilities(terminalText: string, baseDi
       scripts: [...currServ.scripts.keys()],
       txts: [...currServ.textFiles.keys()],
       enums: enums,
-      flags: (schema: unknown) => {
+      flags: (schema: Schema) => {
         if (!Array.isArray(schema)) throw new Error("flags require an array of array");
-        pos2 = schema.map((f: unknown) => {
+        pos2 = schema.map((f) => {
           if (!Array.isArray(f)) throw new Error("flags require an array of array");
           if (f[0].length === 1) return "-" + f[0];
           return "--" + f[0];
diff --git a/src/ThirdParty/acorn-jsx-walk.d.ts b/src/ThirdParty/acorn-jsx-walk.d.ts
index 41b4d7b50d..30e095ac42 100644
--- a/src/ThirdParty/acorn-jsx-walk.d.ts
+++ b/src/ThirdParty/acorn-jsx-walk.d.ts
@@ -1 +1,3 @@
-declare module "acorn-jsx-walk";
+declare module "acorn-jsx-walk" {
+  export function extend(base: any): void;
+}
diff --git a/src/ThirdParty/sprintf-js.d.ts b/src/ThirdParty/sprintf-js.d.ts
deleted file mode 100644
index 6da6a8676a..0000000000
--- a/src/ThirdParty/sprintf-js.d.ts
+++ /dev/null
@@ -1 +0,0 @@
-declare module "sprintf-js";
diff --git a/src/Types/Jsonable.ts b/src/Types/Jsonable.ts
index 42d5cbae1c..db0b311fe5 100644
--- a/src/Types/Jsonable.ts
+++ b/src/Types/Jsonable.ts
@@ -1,3 +1,4 @@
+import { arrayAssert } from "../utils/helpers/typeAssertion";
 import type { IReviverValue } from "../utils/JSONReviver";
 // Versions of js builtin classes that can be converted to and from JSON for use in save files
 
@@ -6,6 +7,7 @@ export class JSONSet<T> extends Set<T> {
     return { ctor: "JSONSet", data: Array.from(this) };
   }
   static fromJSON(value: IReviverValue): JSONSet<any> {
+    arrayAssert(value.data);
     return new JSONSet(value.data);
   }
 }
@@ -16,6 +18,15 @@ export class JSONMap<K, __V> extends Map<K, __V> {
   }
 
   static fromJSON(value: IReviverValue): JSONMap<any, any> {
-    return new JSONMap(value.data);
+    arrayAssert(value.data);
+    for (const item of value.data) {
+      arrayAssert(item);
+      if (item.length !== 2) {
+        console.error("Invalid data passed to JSONMap.fromJSON(). Value:", value);
+        throw new Error(`An item is not an array with exactly 2 items. Its length is ${item.length}.`);
+      }
+    }
+    // We validated the data above, so it's safe to typecast here.
+    return new JSONMap(value.data as [unknown, unknown][]);
   }
 }
diff --git a/src/utils/JSONReviver.ts b/src/utils/JSONReviver.ts
index f9849d4da2..b78fe2d54e 100644
--- a/src/utils/JSONReviver.ts
+++ b/src/utils/JSONReviver.ts
@@ -2,13 +2,14 @@
 import { ObjectValidator, validateObject } from "./Validator";
 import { JSONMap, JSONSet } from "../Types/Jsonable";
 import { loadActionIdentifier } from "../Bladeburner/utils/loadActionIdentifier";
+import { objectAssert } from "./helpers/typeAssertion";
 
 type JsonableClass = (new () => { toJSON: () => IReviverValue }) & {
-  fromJSON: (value: IReviverValue) => any;
+  fromJSON: (value: IReviverValue) => unknown;
   validationData?: ObjectValidator<any>;
 };
 
-export interface IReviverValue<T = any> {
+export interface IReviverValue<T = unknown> {
   ctor: string;
   data: T;
 }
@@ -87,16 +88,23 @@ export function Generic_toJSON<T extends Record<string, any>>(
  * @returns    The object */
 export function Generic_fromJSON<T extends Record<string, any>>(
   ctor: new () => T,
-  // data can actually be anything. We're just pretending it has the right keys for T. Save data is not type validated.
-  data: Record<keyof T, any>,
+  data: unknown,
   keys?: readonly (keyof T)[],
 ): T {
+  objectAssert(data);
   const obj = new ctor();
   // If keys were provided, just load the provided keys (if they are in the data)
   if (keys) {
-    for (const key of keys) {
+    /**
+     * The type of key is "keyof T", but the type of data is Record<string, unknown>. TypeScript won't allow us to use
+     * key as the index of data, so we need to typecast here.
+     */
+    for (const key of keys as string[]) {
       const val = data[key];
-      if (val !== undefined) obj[key] = val;
+      if (val !== undefined) {
+        // @ts-expect-error -- TypeScript won't allow this action: Type 'T' is generic and can only be indexed for reading.
+        obj[key] = val;
+      }
     }
     return obj;
   }
diff --git a/src/utils/helpers/typeAssertion.ts b/src/utils/helpers/typeAssertion.ts
index 30eba63b81..71de528125 100644
--- a/src/utils/helpers/typeAssertion.ts
+++ b/src/utils/helpers/typeAssertion.ts
@@ -1,5 +1,15 @@
 // Various functions for asserting types.
 
+export class TypeAssertionError extends Error {
+  friendlyType: string;
+
+  constructor(message: string, friendlyType: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = this.constructor.name;
+    this.friendlyType = friendlyType;
+  }
+}
+
 /** Function for providing custom error message to throw for a type assertion.
  * @param v: Value to assert type of
  * @param assertFn: Typechecking function to use for asserting type of v.
@@ -12,31 +22,47 @@ export function assert<T>(
   try {
     assertFn(v);
   } catch (e) {
+    if (e instanceof TypeAssertionError) {
+      throw msgFn(e.friendlyType);
+    }
     const type = typeof e === "string" ? e : "unknown";
     throw msgFn(type);
   }
 }
 
 /** Returns the friendlyType of v. arrays are "array" and null is "null". */
-export function getFriendlyType(v: unknown): string {
+function getFriendlyType(v: unknown): string {
   return v === null ? "null" : Array.isArray(v) ? "array" : typeof v;
 }
 
 //All assertion functions used here should return the friendlyType of the input.
 
-/** For non-objects, and for array/null, throws the friendlyType of v. */
-export function objectAssert(v: unknown): asserts v is Partial<Record<string, unknown>> {
+/** For non-objects, and for array/null, throws an error with the friendlyType of v. */
+export function objectAssert(v: unknown): asserts v is Record<string, unknown> {
   const type = getFriendlyType(v);
-  if (type !== "object") throw type;
+  if (type !== "object") {
+    console.error("The value is not an object. Value:", v);
+    throw new TypeAssertionError(
+      `The value is not an object. Its type is ${type}. Its string value is ${String(v)}.`,
+      type,
+    );
+  }
 }
 
-/** For non-string, throws the friendlyType of v. */
+/** For non-string, throws an error with the friendlyType of v. */
 export function stringAssert(v: unknown): asserts v is string {
   const type = getFriendlyType(v);
-  if (type !== "string") throw type;
+  if (type !== "string") {
+    console.error("The value is not a string. Value:", v);
+    throw new TypeAssertionError(`The value is not an string. Its type is ${type}.`, type);
+  }
 }
 
-/** For non-array, throws the friendlyType of v. */
+/** For non-array, throws an error with the friendlyType of v. */
 export function arrayAssert(v: unknown): asserts v is unknown[] {
-  if (!Array.isArray(v)) throw getFriendlyType(v);
+  if (!Array.isArray(v)) {
+    console.error("The value is not an array. Value:", v);
+    const type = getFriendlyType(v);
+    throw new TypeAssertionError(`The value is not an array. Its type is ${type}.`, type);
+  }
 }