diff --git a/__fixtures__/core.ts b/__fixtures__/core.ts
index ac354d81f..38c0ed228 100644
--- a/__fixtures__/core.ts
+++ b/__fixtures__/core.ts
@@ -5,6 +5,7 @@ export const debug = jest.fn<typeof core.debug>()
 export const error = jest.fn<typeof core.error>()
 export const info = jest.fn<typeof core.info>()
 export const getInput = jest.fn<typeof core.getInput>()
+export const isDebug = jest.fn<typeof core.isDebug>()
 export const setOutput = jest.fn<typeof core.setOutput>()
 export const setFailed = jest.fn<typeof core.setFailed>()
 export const warning = jest.fn<typeof core.warning>()
diff --git a/__tests__/main.test.ts b/__tests__/main.test.ts
index e87d3dffd..895720a88 100644
--- a/__tests__/main.test.ts
+++ b/__tests__/main.test.ts
@@ -21,6 +21,7 @@ describe('main.ts', () => {
   beforeEach(() => {
     // Set the action's inputs as return values from core.getInput().
     core.getInput.mockImplementation(() => '500')
+    core.isDebug.mockReturnValue(false)
 
     // Mock the wait function so that it does not actually wait.
     wait.mockImplementation(() => Promise.resolve('done!'))
@@ -42,6 +43,40 @@ describe('main.ts', () => {
     )
   })
 
+  it('Fails fast when input is missing', async () => {
+    core.getInput.mockClear().mockReturnValueOnce('')
+    await run()
+    expect(core.setFailed).toHaveBeenNthCalledWith(
+      1,
+      'Input required and not supplied: milliseconds'
+    )
+    expect(wait).not.toHaveBeenCalled()
+  })
+
+  it('Logs debug info in debug mode', async () => {
+    core.isDebug.mockReturnValue(true)
+    process.env.GITHUB_ACTIONS = 'true'
+    process.env.GITHUB_WORKFLOW = 'ci'
+    process.env.GITHUB_RUN_ID = '123'
+    process.env.GITHUB_SHA = 'deadbeef'
+    process.env.GITHUB_REF = 'refs/heads/main'
+    process.env.RUNNER_OS = 'Linux'
+
+    await run()
+
+    const messages = core.debug.mock.calls.map(call => call[0])
+    expect(messages.some(msg => msg.includes('Node.js version:'))).toBe(true)
+    expect(messages.some(msg => msg.includes('Environment:'))).toBe(true)
+  })
+
+  it('Does not log debug env info without debug mode', async () => {
+    core.isDebug.mockReturnValue(false)
+    await run()
+    const messages = core.debug.mock.calls.map(call => call[0])
+    expect(messages.some(msg => msg.includes('Node.js version:'))).toBe(false)
+    expect(messages.some(msg => msg.includes('Environment:'))).toBe(false)
+  })
+
   it('Sets a failed status', async () => {
     // Clear the getInput mock and return an invalid value.
     core.getInput.mockClear().mockReturnValueOnce('this is not a number')
diff --git a/src/main.ts b/src/main.ts
index d0ee6d394..a53392372 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -10,6 +10,23 @@ export async function run(): Promise<void> {
   try {
     const ms: string = core.getInput('milliseconds')
 
+    if (!ms.trim()) {
+      throw new Error('Input required and not supplied: milliseconds')
+    }
+
+    if (core.isDebug()) {
+      core.debug(`Node.js version: ${process.version}`)
+      const envSummary = {
+        GITHUB_ACTIONS: process.env.GITHUB_ACTIONS,
+        GITHUB_WORKFLOW: process.env.GITHUB_WORKFLOW,
+        GITHUB_RUN_ID: process.env.GITHUB_RUN_ID,
+        GITHUB_SHA: process.env.GITHUB_SHA,
+        GITHUB_REF: process.env.GITHUB_REF,
+        RUNNER_OS: process.env.RUNNER_OS
+      }
+      core.debug(`Environment: ${JSON.stringify(envSummary)}`)
+    }
+
     // Debug logs are only output if the `ACTIONS_STEP_DEBUG` secret is true
     core.debug(`Waiting ${ms} milliseconds ...`)