diff --git a/packages/toolkit/__tests__/toolkit.test.ts b/packages/toolkit/__tests__/toolkit.test.ts
index 0ab2d244..4a7b233f 100644
--- a/packages/toolkit/__tests__/toolkit.test.ts
+++ b/packages/toolkit/__tests__/toolkit.test.ts
@@ -1,29 +1,50 @@
+import {Signale} from 'signale'
+import {ExitCode} from '../src/exit'
 import {Toolkit} from '../src/toolkit'
 
 describe('Toolkit', () => {
-  it('runs a sync function', async () => {
-    const cb = jest.fn(() => true)
-    const value = await Toolkit.run(cb)
-    expect(cb).toHaveBeenCalledWith(expect.any(Toolkit))
-    expect(value).toBe(true)
-  })
-
-  it('runs an async function', async () => {
-    const cb = jest.fn(async () => true)
-    const value = await Toolkit.run(cb)
-    expect(cb).toHaveBeenCalledWith(expect.any(Toolkit))
-    expect(value).toBe(true)
-  })
-
-  it('logs and fails when an error occurs', async () => {
-    const err = new Error()
-    const exitFailure = jest.fn()
-
-    await Toolkit.run(async tk => {
-      tk.exit.failure = exitFailure
-      throw err
+  describe('.run', () => {
+    it('runs a sync function', async () => {
+      const cb = jest.fn(() => true)
+      const value = await Toolkit.run(cb)
+      expect(cb).toHaveBeenCalledWith(expect.any(Toolkit))
+      expect(value).toBe(true)
     })
 
-    expect(exitFailure).toHaveBeenCalledWith(err)
+    it('runs an async function', async () => {
+      const cb = jest.fn(async () => true)
+      const value = await Toolkit.run(cb)
+      expect(cb).toHaveBeenCalledWith(expect.any(Toolkit))
+      expect(value).toBe(true)
+    })
+
+    it('logs and fails when an error occurs', async () => {
+      const err = new Error()
+      const exitFailure = jest.fn()
+
+      await Toolkit.run(async tk => {
+        tk.exit.failure = exitFailure
+        throw err
+      })
+
+      expect(exitFailure).toHaveBeenCalledWith(err)
+    })
+  })
+
+  it('asserts required keys are present', async () => {
+    const missingKey = '__DOES_NOT_EXIST__'
+
+    Reflect.deleteProperty(process.env, missingKey)
+
+    const logger = new Signale()
+    logger.fatal = jest.fn()
+    jest.spyOn(process, 'exit').mockImplementation()
+
+    new Toolkit({logger, requiredEnv: [missingKey]})
+
+    expect(process.exit).toHaveBeenCalledWith(ExitCode.Failure)
+    expect(logger.fatal)
+      .toHaveBeenCalledWith(`The following environment variables are required for this action to run:
+- __DOES_NOT_EXIST__`)
   })
 })
diff --git a/packages/toolkit/src/toolkit.ts b/packages/toolkit/src/toolkit.ts
index 620757f7..255b9c48 100644
--- a/packages/toolkit/src/toolkit.ts
+++ b/packages/toolkit/src/toolkit.ts
@@ -3,6 +3,23 @@ import {Exit} from './exit'
 
 export type ActionFn = (tools: Toolkit) => unknown
 
+/**
+ * Options used to customize an instance of [[Toolkit]]
+ */
+export type ToolkitOptions = {
+  /**
+   * A custom Signale instance to use
+   */
+  logger?: Signale
+
+  /**
+   * A list of environment variable names this action requires in order to run
+   *
+   * If any of them are missing, the action will fail and log the missing keys.
+   */
+  requiredEnv?: string[]
+}
+
 /**
  * A set of tools for the Actions runtime
  */
@@ -13,8 +30,8 @@ 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) {
-    const tools = new Toolkit()
+  static async run(func: ActionFn, opts?: ToolkitOptions) {
+    const tools = new Toolkit(opts)
 
     try {
       const ret = func(tools)
@@ -27,26 +44,45 @@ export class Toolkit {
   /**
    * A logger for the toolkit, an instance of [Signale](https://github.com/klaussinani/signale)
    */
-  readonly logger: Signale & LoggerFunc = this.wrapLogger(
-    new Signale({
-      config: {
-        underlineLabel: false
-      }
-    })
-  )
+  readonly logger: Signale & LoggerFunc
 
   /**
    * A wrapper around an instance of [[Exit]]
    */
-  readonly exit: Exit = new Exit(this.logger)
+  readonly exit: Exit
 
   /**
    * The authentication token for the GitHub API
    */
   readonly token: string = process.env.GITHUB_TOKEN || ''
 
+  constructor(opts: ToolkitOptions = {}) {
+    const logger = opts.logger || new Signale({config: {underlineLabel: false}})
+    this.logger = this.wrapLogger(logger)
+    this.exit = new Exit(this.logger)
+
+    if (opts.requiredEnv) {
+      this.checkRequiredEnv(opts.requiredEnv)
+    }
+  }
+
   /**
-   * Wrap a Signale logger so that its a callable class
+   * Ensure that the given keys are in the environment.
+   */
+  private checkRequiredEnv(keys: string[]) {
+    const missingEnv = keys.filter(key => !process.env.hasOwnProperty(key))
+
+    if (missingEnv.length === 0) return
+
+    const list = missingEnv.map(key => `- ${key}`).join('\n')
+
+    this.exit.failure(
+      `The following environment variables are required for this action to run:\n${list}`
+    )
+  }
+
+  /**
+   * Wrap a Signale logger so that its a callable class.
    */
   private wrapLogger(logger: Signale) {
     // Create a callable function