diff --git a/eslint.config.mjs b/eslint.config.mjs
index a25433e..fc00f9f 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -9,7 +9,6 @@ export default tseslint.config(
     {
         rules: {
             // TODO: Remove ignored rules and fix the code
-            "@typescript-eslint/no-explicit-any": "off",
             "@typescript-eslint/no-this-alias": "off",
             "@typescript-eslint/no-unused-vars": "off",
             "@typescript-eslint/no-var-requires": "off",
diff --git a/examples/express-sample/package-lock.json b/examples/express-sample/package-lock.json
index fcbae9b..c70a2f9 100644
--- a/examples/express-sample/package-lock.json
+++ b/examples/express-sample/package-lock.json
@@ -21,6 +21,7 @@
       }
     },
     "../..": {
+      "name": "raygun",
       "version": "0.13.2",
       "dependencies": {
         "@types/express": "^4.17.21",
@@ -30,9 +31,11 @@
         "uuid": "^9.0.1"
       },
       "devDependencies": {
+        "@eslint/js": "^9.1.1",
         "@types/node": "^20.12.7",
         "@types/stack-trace": "0.0.33",
         "@types/uuid": "^9.0.8",
+        "eslint": "^8.57.0",
         "express": "^4.19.2",
         "http-terminator": "^3.2.0",
         "jshint": "^2.13.6",
@@ -41,10 +44,8 @@
         "semver": "^7.6.0",
         "tap": "^18.7.2",
         "ts-node": "^10.9.2",
-        "tslint": "^6.1.1",
-        "tslint-config-prettier": "^1.18.0",
-        "tslint-react": "^5.0.0",
         "typescript": "^5.4.5",
+        "typescript-eslint": "^7.7.1",
         "verror": "^1.10.1"
       },
       "engines": {
diff --git a/lib/raygun.batch.ts b/lib/raygun.batch.ts
index 05cb9de..cc4ccf1 100644
--- a/lib/raygun.batch.ts
+++ b/lib/raygun.batch.ts
@@ -32,7 +32,7 @@ export const MAX_BATCH_SIZE_BYTES = 1638400;
 const MAX_BATCH_INNER_SIZE_BYTES = MAX_BATCH_SIZE_BYTES - 2; // for the starting and ending byte
 
 export class RaygunBatchTransport {
-  private timerId: any | null = null;
+  private timerId: NodeJS.Timeout | null = null;
   private httpOptions: HTTPOptions;
   private interval: number;
   private batchId: number = 0;
diff --git a/lib/raygun.messageBuilder.ts b/lib/raygun.messageBuilder.ts
index 64bfb19..cc43a95 100644
--- a/lib/raygun.messageBuilder.ts
+++ b/lib/raygun.messageBuilder.ts
@@ -31,18 +31,21 @@ type UserMessageData = RawUserData | string | undefined;
 const humanString = require("object-to-human-string");
 const packageDetails = require("../package.json");
 
-function filterKeys(obj: { [key: string]: any }, filters: string[]) {
+function filterKeys(obj: object, filters: string[]): object {
   if (!obj || !filters || typeof obj !== "object") {
     return obj;
   }
+  // Make temporary copy of the object to avoid mutating the original
+  // Cast to Record<string, object> to enforce type check and avoid using any
+  const _obj = { ...obj } as Record<string, object>;
   Object.keys(obj).forEach(function (i) {
     if (filters.indexOf(i) > -1) {
-      delete obj[i];
+      delete _obj[i];
     } else {
-      obj[i] = filterKeys(obj[i], filters);
+      _obj[i] = filterKeys(_obj[i], filters);
     }
   });
-  return obj;
+  return _obj;
 }
 
 function getStackTrace(
@@ -126,7 +129,8 @@ export class RaygunMessageBuilder {
     return this.message as Message;
   }
 
-  setErrorDetails(error: any) {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  setErrorDetails(error: Error | string | any) {
     if (
       !(error instanceof Error) &&
       typeof error !== "string" &&
diff --git a/lib/raygun.sync.worker.ts b/lib/raygun.sync.worker.ts
index 46c4386..9f915df 100644
--- a/lib/raygun.sync.worker.ts
+++ b/lib/raygun.sync.worker.ts
@@ -1,17 +1,17 @@
 import fs from "fs";
-
 import * as transport from "./raygun.transport";
 import { SendOptions, SendOptionsWithoutCB } from "./types";
+import { IncomingMessage } from "http";
 
 // Read stdin synchronously
 const data = fs.readFileSync(0, "utf-8");
 
 const options: SendOptionsWithoutCB = JSON.parse(data);
-const sendOptions = { ...options, callback };
+const sendOptions: SendOptions = { ...options, callback };
 
 transport.send(sendOptions);
 
-function callback(error: Error | null, result: any) {
+function callback(error: Error | null, result: IncomingMessage | null) {
   if (error) {
     console.log("Error sending with sync transport", error);
   } else {
diff --git a/lib/types.ts b/lib/types.ts
index 410e792..9e18ffa 100644
--- a/lib/types.ts
+++ b/lib/types.ts
@@ -1,8 +1,9 @@
 import type { IncomingMessage } from "http";
 
-export type IndexableError = Error & {
-  [key: string]: any;
-};
+// IndexableError is a type that extends the Error type
+// and allows for any additional properties to be added to it.
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type IndexableError = Error & Record<string, any>;
 
 export type MessageBuilderOptions = {
   reportColumnNumbers?: boolean;
@@ -80,6 +81,8 @@ export type HTTPOptions = {
   apiKey: string;
 };
 
+// Allow any because users are free to set anything as CustomData
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
 export type CustomData = any;
 
 export type RequestParams = ({ host: string } | { hostname: string }) &