diff --git a/.changeset/invalid-key-cli-error.md b/.changeset/invalid-key-cli-error.md
new file mode 100644
index 00000000000..b45981f8b61
--- /dev/null
+++ b/.changeset/invalid-key-cli-error.md
@@ -0,0 +1,6 @@
+---
+'@clerk/shared': patch
+'@clerk/nextjs': patch
+---
+
+Invalid publishable key errors now recommend the Clerk CLI: the shared invalid-key message points at `npx clerk@latest init`, and `clerkMiddleware()` validates the publishable key format upfront, throwing a setup error in development (`npx clerk@latest init`) or a deploy-oriented error in production (`npx clerk@latest env pull --instance prod`) instead of failing later with `Publishable key not valid.`
diff --git a/packages/nextjs/src/server/__tests__/clerkMiddlewareInvalidKeys.test.ts b/packages/nextjs/src/server/__tests__/clerkMiddlewareInvalidKeys.test.ts
new file mode 100644
index 00000000000..993c2ed8c76
--- /dev/null
+++ b/packages/nextjs/src/server/__tests__/clerkMiddlewareInvalidKeys.test.ts
@@ -0,0 +1,59 @@
+import { automatedEnvironmentVariables } from '@clerk/shared/utils';
+import type { NextFetchEvent } from 'next/server';
+import { NextRequest } from 'next/server';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+// The mock SHOULD exist before the imports: keys are present but not parseable as Clerk keys, so
+// the invalid-key error path is reachable.
+vi.mock(import('../constants.js'), async importOriginal => {
+  const actual = await importOriginal();
+  return {
+    ...actual,
+    PUBLISHABLE_KEY: 'pk_test_placeholder',
+    SECRET_KEY: 'sk_test_placeholder',
+  };
+});
+
+describe('clerkMiddleware when Clerk env vars are invalid', () => {
+  beforeEach(() => {
+    vi.stubEnv('NODE_ENV', 'development');
+    automatedEnvironmentVariables.forEach(name => {
+      vi.stubEnv(name, undefined);
+      vi.stubGlobal(name, undefined);
+    });
+    vi.resetModules();
+  });
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+    vi.unstubAllGlobals();
+    vi.resetModules();
+  });
+
+  const runMiddleware = async () => {
+    const { clerkMiddleware } = await import('../clerkMiddleware.js');
+    const request = new NextRequest('https://example.com/protected');
+    return clerkMiddleware()(request, {} as NextFetchEvent);
+  };
+
+  it('throws the invalid-key error pointing at the CLI', async () => {
+    await expect(runMiddleware()).rejects.toThrow(/npx clerk@latest init/);
+    await expect(runMiddleware()).rejects.toThrow(/\(code=invalid_env_keys\)/);
+  });
+
+  it('throws the production invalid-key error pointing at env pull', async () => {
+    vi.stubEnv('NODE_ENV', 'production');
+    await expect(runMiddleware()).rejects.toThrow(/npx clerk@latest env pull --instance prod/);
+    await expect(runMiddleware()).rejects.toThrow(/\(code=invalid_env_keys_production\)/);
+  });
+
+  it('names the env var and the expected key format in the message', async () => {
+    const { invalidEnvKeys, productionInvalidEnvKeys } = await import('../errors.js');
+    for (const message of [invalidEnvKeys, productionInvalidEnvKeys]) {
+      expect(message).toContain('NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY');
+      expect(message).toContain('pk_test_');
+    }
+    expect(invalidEnvKeys).toContain('npx clerk@latest init');
+    expect(productionInvalidEnvKeys).toContain('npx clerk@latest env pull --instance prod');
+  });
+});
diff --git a/packages/nextjs/src/server/clerkMiddleware.ts b/packages/nextjs/src/server/clerkMiddleware.ts
index 866d4ea95e5..1d6d3b8f316 100644
--- a/packages/nextjs/src/server/clerkMiddleware.ts
+++ b/packages/nextjs/src/server/clerkMiddleware.ts
@@ -38,7 +38,7 @@ import { canUseKeyless } from '../utils/feature-flags';
 import { clerkClient } from './clerkClient';
 import { DOMAIN, PROXY_URL, PUBLISHABLE_KEY, SECRET_KEY, SIGN_IN_URL, SIGN_UP_URL } from './constants';
 import { type ContentSecurityPolicyOptions, createContentSecurityPolicyHeaders } from './content-security-policy';
-import { keylessMissingEnvVars, productionMissingEnvVars } from './errors';
+import { invalidEnvKeys, keylessMissingEnvVars, productionInvalidEnvKeys, productionMissingEnvVars } from './errors';
 import { errorThrower } from './errorThrower';
 import { clerkMiddlewareRequestDataStorage, clerkMiddlewareRequestDataStore } from './middleware-storage';
 import {
@@ -163,6 +163,10 @@ export const clerkMiddleware = ((...args: unknown[]): NextMiddleware | NextMiddl
         throw new Error(productionMissingEnvVars);
       });
 
+      if (!parsePublishableKey(publishableKey)) {
+        throw new Error(isDevelopmentEnvironment() ? invalidEnvKeys : productionInvalidEnvKeys);
+      }
+
       // Handle Frontend API proxy requests early, before authentication
       const requestUrl = new URL(request.nextUrl.href);
       let frontendApiProxyConfig = resolvedParams.frontendApiProxy;
diff --git a/packages/nextjs/src/server/errors.ts b/packages/nextjs/src/server/errors.ts
index cdebd4702db..8e73ad23fd8 100644
--- a/packages/nextjs/src/server/errors.ts
+++ b/packages/nextjs/src/server/errors.ts
@@ -50,6 +50,22 @@ To deploy this application to production, run:
 
 This provisions a production Clerk instance and walks you through DNS and OAuth setup. If you already have a production instance, run \`npx clerk@latest env pull --instance prod\` to write its keys to your env file, and set the same keys in your deployment environment. (code=missing_env_keys_production)`;
 
+export const invalidEnvKeys = `Clerk: Invalid environment keys. NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY is set but is not a valid Clerk publishable key (expected format: pk_test_... or pk_live_...).
+
+To set up Clerk for this project with valid keys, run:
+
+  npx clerk@latest init
+
+The command is non-interactive and requires no Clerk account or login: it provisions temporary development keys automatically and writes them to your .env.local file. Then restart your dev server. Do not invent placeholder keys - they will fail. If you already have a Clerk application, copy its keys from https://dashboard.clerk.com into .env.local instead. (code=invalid_env_keys)`;
+
+export const productionInvalidEnvKeys = `Clerk: Invalid environment keys. NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY is set but is not a valid Clerk publishable key (expected format: pk_test_... or pk_live_...).
+
+To write the keys of an existing Clerk instance to your env file, run:
+
+  npx clerk@latest env pull --instance prod
+
+Set the same keys in your deployment environment. If you do not have a production Clerk instance yet, run \`npx clerk@latest deploy\` to provision one. (code=invalid_env_keys_production)`;
+
 export const authSignatureInvalid = `Clerk: Unable to verify request, this usually means the Clerk middleware did not run. Ensure Clerk's middleware is properly integrated and matches the current route. For more information, see: https://clerk.com/docs/reference/nextjs/clerk-middleware. (code=auth_signature_invalid)`;
 
 export const encryptionKeyInvalid = `Clerk: Unable to decrypt request data, this usually means the encryption key is invalid. Ensure the encryption key is properly set. For more information, see: https://clerk.com/docs/reference/nextjs/clerk-middleware#dynamic-keys. (code=encryption_key_invalid)`;
diff --git a/packages/shared/src/__tests__/error.spec.ts b/packages/shared/src/__tests__/error.spec.ts
index 6c347f58994..17df7462f50 100644
--- a/packages/shared/src/__tests__/error.spec.ts
+++ b/packages/shared/src/__tests__/error.spec.ts
@@ -16,7 +16,7 @@ describe('ErrorThrower', () => {
 
   it('throws the correct error message and interpolates pkg and known parameters', () => {
     expect(() => errorThrower.throwInvalidPublishableKeyError({ key: 'whatever' })).toThrow(
-      '@clerk/test-package: The publishableKey passed to Clerk is invalid. You can get your Publishable key at https://dashboard.clerk.com/last-active?path=api-keys. (key=whatever)',
+      '@clerk/test-package: The publishableKey passed to Clerk is invalid (key=whatever). To create a Clerk application with valid keys, run:',
     );
   });
 
diff --git a/packages/shared/src/errors/errorThrower.ts b/packages/shared/src/errors/errorThrower.ts
index 1c2c7f5cf42..a6c23db0ce9 100644
--- a/packages/shared/src/errors/errorThrower.ts
+++ b/packages/shared/src/errors/errorThrower.ts
@@ -1,6 +1,10 @@
 const DefaultMessages = Object.freeze({
   InvalidProxyUrlErrorMessage: `The proxyUrl passed to Clerk is invalid. The expected value for proxyUrl is an absolute URL or a relative path with a leading '/'. (key={{url}})`,
-  InvalidPublishableKeyErrorMessage: `The publishableKey passed to Clerk is invalid. You can get your Publishable key at https://dashboard.clerk.com/last-active?path=api-keys. (key={{key}})`,
+  InvalidPublishableKeyErrorMessage: `The publishableKey passed to Clerk is invalid (key={{key}}). To create a Clerk application with valid keys, run:
+
+  npx clerk@latest init
+
+Do not invent placeholder keys - they will fail. If you already have a Clerk application, copy its Publishable key from https://dashboard.clerk.com/last-active?path=api-keys instead.`,
   MissingPublishableKeyErrorMessage: `Missing publishableKey. To set up Clerk for this project, run:
 
   npx clerk@latest init