diff --git a/.eslintrc.json b/.eslintrc.json
index 241986aa..a427f9e5 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -4,14 +4,53 @@
   "parser": "@typescript-eslint/parser",
   "parserOptions": {
     "ecmaVersion": 9,
-    "sourceType": "module"
+    "sourceType": "module",
+    "project": "./tsconfig.json"
   },
   "rules": {
-    "no-unused-vars": "off",
     "eslint-comments/no-use": "off",
     "import/no-namespace": "off",
+    "no-unused-vars": "off",
     "@typescript-eslint/no-unused-vars": "error",
-    "@typescript-eslint/explicit-member-accessibility": ["error", {"accessibility": "no-public"}]
+    "@typescript-eslint/explicit-member-accessibility": ["error", {"accessibility": "no-public"}],
+    "@typescript-eslint/no-require-imports": "error",
+    "@typescript-eslint/array-type": "error",
+    "@typescript-eslint/await-thenable": "error",
+    "@typescript-eslint/ban-ts-ignore": "error",
+    "camelcase": "off",
+    "@typescript-eslint/camelcase": "error",
+    "@typescript-eslint/class-name-casing": "error",
+    "@typescript-eslint/explicit-function-return-type": ["error", {"allowExpressions": true}],
+    "@typescript-eslint/func-call-spacing": ["error", "never"],
+    "@typescript-eslint/generic-type-naming": ["error", "^[A-Z][A-Za-z]*$"],
+    "@typescript-eslint/no-array-constructor": "error",
+    "@typescript-eslint/no-empty-interface": "error",
+    "@typescript-eslint/no-explicit-any": "error",
+    "no-extra-parens": "off",
+    "@typescript-eslint/no-extra-parens": "error",
+    "@typescript-eslint/no-extraneous-class": "error",
+    "@typescript-eslint/no-for-in-array": "error",
+    "@typescript-eslint/no-inferrable-types": "error",
+    "@typescript-eslint/no-misused-new": "error",
+    "@typescript-eslint/no-namespace": "error",
+    "@typescript-eslint/no-non-null-assertion": "warn",
+    "@typescript-eslint/no-object-literal-type-assertion": "error",
+    "@typescript-eslint/no-unnecessary-qualifier": "error",
+    "@typescript-eslint/no-unnecessary-type-assertion": "error",
+    "@typescript-eslint/no-useless-constructor": "error",
+    "@typescript-eslint/no-var-requires": "error",
+    "@typescript-eslint/prefer-for-of": "warn",
+    "@typescript-eslint/prefer-function-type": "warn",
+    "@typescript-eslint/prefer-includes": "error",
+    "@typescript-eslint/prefer-interface": "error",
+    "@typescript-eslint/prefer-string-starts-ends-with": "error",
+    "@typescript-eslint/promise-function-async": "error",
+    "@typescript-eslint/require-array-sort-compare": "error",
+    "@typescript-eslint/restrict-plus-operands": "error",
+    "semi": "off",
+    "@typescript-eslint/semi": ["error", "never"],
+    "@typescript-eslint/type-annotation-spacing": "error",
+    "@typescript-eslint/unbound-method": "error"
   },
   "env": {
     "node": true,
diff --git a/packages/core/__tests__/lib.test.ts b/packages/core/__tests__/lib.test.ts
index a21b51e1..b1f638c8 100644
--- a/packages/core/__tests__/lib.test.ts
+++ b/packages/core/__tests__/lib.test.ts
@@ -1,6 +1,9 @@
+import {ExitCode} from '@actions/exit'
 import * as os from 'os'
 import * as core from '../src/core'
 
+/* eslint-disable @typescript-eslint/unbound-method */
+
 const testEnvVars = {
   'my var': '',
   'special char var \r\n];': '',
@@ -103,18 +106,18 @@ describe('@actions/core', () => {
 
   it('setNeutral sets the correct exit code', () => {
     core.setFailed('Failure message')
-    expect(process.exitCode).toBe(1)
+    expect(process.exitCode).toBe(ExitCode.Failure)
   })
 
   it('setFailure sets the correct exit code and failure message', () => {
     core.setFailed('Failure message')
-    expect(process.exitCode).toBe(1)
+    expect(process.exitCode).toBe(ExitCode.Failure)
     assertWriteCalls([`##[error]Failure message${os.EOL}`])
   })
 
   it('setFailure escapes the failure message', () => {
     core.setFailed('Failure \r\n\nmessage\r')
-    expect(process.exitCode).toBe(1)
+    expect(process.exitCode).toBe(ExitCode.Failure)
     assertWriteCalls([`##[error]Failure %0D%0A%0Amessage%0D${os.EOL}`])
   })
 
@@ -150,7 +153,7 @@ describe('@actions/core', () => {
 })
 
 // Assert that process.stdout.write calls called only with the given arguments.
-function assertWriteCalls(calls: string[]) {
+function assertWriteCalls(calls: string[]): void {
   expect(process.stdout.write).toHaveBeenCalledTimes(calls.length)
 
   for (let i = 0; i < calls.length; i++) {
diff --git a/packages/core/src/command.ts b/packages/core/src/command.ts
index b277bfb2..73c27aed 100644
--- a/packages/core/src/command.ts
+++ b/packages/core/src/command.ts
@@ -2,6 +2,10 @@ import * as os from 'os'
 
 // For internal use, subject to change.
 
+interface CommandProperties {
+  [key: string]: string
+}
+
 /**
  * Commands
  *
@@ -14,25 +18,25 @@ import * as os from 'os'
  */
 export function issueCommand(
   command: string,
-  properties: any,
+  properties: CommandProperties,
   message: string
-) {
+): void {
   const cmd = new Command(command, properties, message)
   process.stdout.write(cmd.toString() + os.EOL)
 }
 
-export function issue(name: string, message: string) {
+export function issue(name: string, message: string): void {
   issueCommand(name, {}, message)
 }
 
 const CMD_PREFIX = '##['
 
 class Command {
-  constructor(
-    command: string,
-    properties: {[key: string]: string},
-    message: string
-  ) {
+  private readonly command: string
+  private readonly message: string
+  private readonly properties: CommandProperties
+
+  constructor(command: string, properties: CommandProperties, message: string) {
     if (!command) {
       command = 'missing.command'
     }
@@ -42,11 +46,7 @@ class Command {
     this.message = message
   }
 
-  command: string
-  message: string
-  properties: {[key: string]: string}
-
-  toString() {
+  toString(): string {
     let cmdStr = CMD_PREFIX + this.command
 
     if (this.properties && Object.keys(this.properties).length > 0) {
@@ -67,7 +67,7 @@ class Command {
 
     // safely append the message - avoid blowing up when attempting to
     // call .replace() if message is not a string for some reason
-    const message: string = `${this.message || ''}`
+    const message = `${this.message || ''}`
     cmdStr += escapeData(message)
 
     return cmdStr
diff --git a/packages/core/src/core.ts b/packages/core/src/core.ts
index 408b9ad1..f63ef1c6 100644
--- a/packages/core/src/core.ts
+++ b/packages/core/src/core.ts
@@ -18,7 +18,7 @@ export interface InputOptions {
  * @param name the name of the variable to set
  * @param val the value of the variable
  */
-export function exportVariable(name: string, val: string) {
+export function exportVariable(name: string, val: string): void {
   process.env[name] = val
   issueCommand('set-env', {name}, val)
 }
@@ -28,7 +28,7 @@ export function exportVariable(name: string, val: string) {
  * @param name the name of the variable to set
  * @param val value of the secret
  */
-export function exportSecret(name: string, val: string) {
+export function exportSecret(name: string, val: string): void {
   exportVariable(name, val)
   issueCommand('set-secret', {}, val)
 }
@@ -57,7 +57,7 @@ export function getInput(name: string, options?: InputOptions): string {
 /**
  * Sets the action status to neutral
  */
-export function setNeutral() {
+export function setNeutral(): void {
   process.exitCode = ExitCode.Neutral
 }
 
@@ -66,7 +66,7 @@ export function setNeutral() {
  * When the action exits it will be with an exit code of 1
  * @param message add error issue message
  */
-export function setFailed(message: string) {
+export function setFailed(message: string): void {
   process.exitCode = ExitCode.Failure
   error(message)
 }
@@ -79,7 +79,7 @@ export function setFailed(message: string) {
  * Writes debug message to user log
  * @param message debug message
  */
-export function debug(message: string) {
+export function debug(message: string): void {
   issueCommand('debug', {}, message)
 }
 
@@ -87,7 +87,7 @@ export function debug(message: string) {
  * Adds an error issue
  * @param message error issue message
  */
-export function error(message: string) {
+export function error(message: string): void {
   issue('error', message)
 }
 
@@ -95,6 +95,6 @@ export function error(message: string) {
  * Adds an warning issue
  * @param message warning issue message
  */
-export function warning(message: string) {
+export function warning(message: string): void {
   issue('warning', message)
 }
diff --git a/packages/exit/__tests__/exit.test.ts b/packages/exit/__tests__/exit.test.ts
index 31ae074f..f7de0e99 100644
--- a/packages/exit/__tests__/exit.test.ts
+++ b/packages/exit/__tests__/exit.test.ts
@@ -1,5 +1,7 @@
 import * as exit from '../src/exit'
 
+/* eslint-disable @typescript-eslint/unbound-method */
+
 it('exits successfully', () => {
   jest.spyOn(process, 'exit').mockImplementation()
   exit.success()
diff --git a/packages/exit/src/exit.ts b/packages/exit/src/exit.ts
index ecea2961..81ef86e2 100644
--- a/packages/exit/src/exit.ts
+++ b/packages/exit/src/exit.ts
@@ -24,20 +24,20 @@ export enum ExitCode {
 /**
  * Exit the action as a success.
  */
-export function success() {
+export function success(): void {
   process.exit(ExitCode.Success)
 }
 
 /**
  * Exit the action as a failure.
  */
-export function failure() {
+export function failure(): void {
   process.exit(ExitCode.Failure)
 }
 
 /**
  * Exit the action neither a success or a failure
  */
-export function neutral() {
+export function neutral(): void {
   process.exit(ExitCode.Neutral)
 }
diff --git a/packages/toolkit/__tests__/exit.test.ts b/packages/toolkit/__tests__/exit.test.ts
index d3901977..f7e1111b 100644
--- a/packages/toolkit/__tests__/exit.test.ts
+++ b/packages/toolkit/__tests__/exit.test.ts
@@ -2,6 +2,8 @@ import * as exitPkg from '@actions/exit'
 import {Signale} from 'signale'
 import {Exit} from '../src/exit'
 
+/* eslint-disable @typescript-eslint/unbound-method */
+
 jest.mock('@actions/exit')
 
 const tests: [keyof Exit, keyof Signale][] = [
diff --git a/packages/toolkit/__tests__/toolkit.test.ts b/packages/toolkit/__tests__/toolkit.test.ts
index d8dd3254..2a88b4d8 100644
--- a/packages/toolkit/__tests__/toolkit.test.ts
+++ b/packages/toolkit/__tests__/toolkit.test.ts
@@ -2,6 +2,8 @@ import * as exitPkg from '@actions/exit'
 import {Signale} from 'signale'
 import {Toolkit} from '../src/toolkit'
 
+/* eslint-disable @typescript-eslint/unbound-method */
+
 jest.mock('@actions/exit')
 
 describe('.run', () => {
diff --git a/packages/toolkit/src/exit.ts b/packages/toolkit/src/exit.ts
index 69000aac..101a4dd7 100644
--- a/packages/toolkit/src/exit.ts
+++ b/packages/toolkit/src/exit.ts
@@ -10,7 +10,7 @@ export class Exit {
   /**
    * Stop the action with a "success" status.
    */
-  success(message?: string) {
+  success(message?: string): void {
     if (message) this.logger.success(message)
     exit.success()
   }
@@ -18,7 +18,7 @@ export class Exit {
   /**
    * Stop the action with a "neutral" status.
    */
-  neutral(message?: string) {
+  neutral(message?: string): void {
     if (message) this.logger.info(message)
     exit.neutral()
   }
@@ -26,7 +26,7 @@ export class Exit {
   /**
    * Stop the action with a "failed" status.
    */
-  failure(message?: string) {
+  failure(message?: string): void {
     if (message) this.logger.fatal(message)
     exit.failure()
   }
diff --git a/packages/toolkit/src/toolkit.ts b/packages/toolkit/src/toolkit.ts
index 255b9c48..4d563473 100644
--- a/packages/toolkit/src/toolkit.ts
+++ b/packages/toolkit/src/toolkit.ts
@@ -6,7 +6,7 @@ export type ActionFn = (tools: Toolkit) => unknown
 /**
  * Options used to customize an instance of [[Toolkit]]
  */
-export type ToolkitOptions = {
+export interface ToolkitOptions {
   /**
    * A custom Signale instance to use
    */
@@ -30,7 +30,7 @@ export class Toolkit {
    * If an error occurs, the error will be logged and the action will exit as a
    * failure.
    */
-  static async run(func: ActionFn, opts?: ToolkitOptions) {
+  static async run(func: ActionFn, opts?: ToolkitOptions): Promise<void> {
     const tools = new Toolkit(opts)
 
     try {
@@ -69,7 +69,7 @@ export class Toolkit {
   /**
    * Ensure that the given keys are in the environment.
    */
-  private checkRequiredEnv(keys: string[]) {
+  private checkRequiredEnv(keys: string[]): void {
     const missingEnv = keys.filter(key => !process.env.hasOwnProperty(key))
 
     if (missingEnv.length === 0) return
@@ -84,7 +84,7 @@ export class Toolkit {
   /**
    * Wrap a Signale logger so that its a callable class.
    */
-  private wrapLogger(logger: Signale) {
+  private wrapLogger(logger: Signale): Signale & LoggerFunc {
     // Create a callable function
     const fn = logger.info.bind(logger)
     // Add the log methods onto the function