diff --git a/packages/docusaurus-utils/src/constants.ts b/packages/docusaurus-utils/src/constants.ts
index a9a91394f48c..633f365f38fc 100644
--- a/packages/docusaurus-utils/src/constants.ts
+++ b/packages/docusaurus-utils/src/constants.ts
@@ -29,8 +29,11 @@ export const DEFAULT_BUILD_DIR_NAME = 'build';
 /**
  * Can be overridden with cli option `--config`. Code should generally use
  * `context.siteConfigPath` instead (which is always absolute).
+ *
+ * This does not have extensions, so that we can substitute different ones
+ * when resolving the path.
  */
-export const DEFAULT_CONFIG_FILE_NAME = 'docusaurus.config.js';
+export const DEFAULT_CONFIG_FILE_NAME = 'docusaurus.config';
 
 /** Can be absolute or relative to site directory. */
 export const BABEL_CONFIG_FILE_NAME =
diff --git a/packages/docusaurus/src/server/__tests__/__fixtures__/config/docusaurus.config.cjs b/packages/docusaurus/src/server/__tests__/__fixtures__/config/docusaurus.config.cjs
new file mode 100644
index 000000000000..22c3d0c6ceef
--- /dev/null
+++ b/packages/docusaurus/src/server/__tests__/__fixtures__/config/docusaurus.config.cjs
@@ -0,0 +1,5 @@
+module.exports = {
+  title: 'title',
+  url: 'https://example.com',
+  baseUrl: '/'
+};
diff --git a/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap b/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
index abaaab349c57..165c2e74ba6a 100644
--- a/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
+++ b/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
@@ -1,5 +1,54 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`loadSiteConfig website with .cjs siteConfig 1`] = `
+{
+  "siteConfig": {
+    "baseUrl": "/",
+    "baseUrlIssueBanner": true,
+    "clientModules": [
+      "foo.js",
+    ],
+    "customFields": {},
+    "favicon": "img/docusaurus.ico",
+    "i18n": {
+      "defaultLocale": "en",
+      "localeConfigs": {},
+      "locales": [
+        "en",
+      ],
+    },
+    "noIndex": false,
+    "onBrokenLinks": "throw",
+    "onBrokenMarkdownLinks": "warn",
+    "onDuplicateRoutes": "warn",
+    "organizationName": "endiliey",
+    "plugins": [
+      [
+        "@docusaurus/plugin-content-docs",
+        {
+          "path": "../docs",
+        },
+      ],
+      "@docusaurus/plugin-content-pages",
+    ],
+    "presets": [],
+    "projectName": "hello",
+    "scripts": [],
+    "staticDirectories": [
+      "static",
+    ],
+    "stylesheets": [],
+    "tagline": "Hello World",
+    "themeConfig": {},
+    "themes": [],
+    "title": "Hello",
+    "titleDelimiter": "|",
+    "url": "https://docusaurus.io",
+  },
+  "siteConfigPath": "<PROJECT_ROOT>/packages/docusaurus/src/server/__tests__/__fixtures__/simple-site/docusaurus.config.js",
+}
+`;
+
 exports[`loadSiteConfig website with valid async config 1`] = `
 {
   "siteConfig": {
diff --git a/packages/docusaurus/src/server/__tests__/config.test.ts b/packages/docusaurus/src/server/__tests__/config.test.ts
index 4965d60f5a05..ba713d997562 100644
--- a/packages/docusaurus/src/server/__tests__/config.test.ts
+++ b/packages/docusaurus/src/server/__tests__/config.test.ts
@@ -19,6 +19,14 @@ describe('loadSiteConfig', () => {
     expect(config).not.toEqual({});
   });
 
+  it('website with .cjs siteConfig', async () => {
+    const config = await loadSiteConfig({
+      siteDir: path.join(__dirname, '__fixtures__', 'simple-site'),
+    });
+    expect(config).toMatchSnapshot();
+    expect(config).not.toEqual({});
+  });
+
   it('website with valid config creator function', async () => {
     const config = await loadSiteConfig({
       siteDir,
@@ -65,7 +73,7 @@ describe('loadSiteConfig', () => {
         customConfigFilePath: 'wrong.config.js',
       }),
     ).rejects.toThrowErrorMatchingInlineSnapshot(`
-            "These field(s) ("useLessField",) are not recognized in docusaurus.config.js.
+            "These field(s) ("useLessField",) are not recognized in wrong.config.js.
             If you still want these fields to be in your configuration, put them in the "customFields" field.
             See https://docusaurus.io/docs/api/docusaurus-config/#customfields"
           `);
diff --git a/packages/docusaurus/src/server/__tests__/configValidation.test.ts b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
index 70eaa3900e3c..0c41cd540db6 100644
--- a/packages/docusaurus/src/server/__tests__/configValidation.test.ts
+++ b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
@@ -18,7 +18,8 @@ const baseConfig: DocusaurusConfig = {
   url: 'https://mysite.com',
 };
 
-const normalizeConfig = (config) => validateConfig({...baseConfig, ...config});
+const normalizeConfig = (config) =>
+  validateConfig({...baseConfig, ...config}, 'docusaurus.config.js');
 
 describe('normalizeConfig', () => {
   it('normalizes empty config', () => {
@@ -289,13 +290,16 @@ describe('normalizeConfig', () => {
 
   it('throws error for required fields', () => {
     expect(() =>
-      validateConfig({
-        invalidField: true,
-        presets: {},
-        stylesheets: {},
-        themes: {},
-        scripts: {},
-      }),
+      validateConfig(
+        {
+          invalidField: true,
+          presets: {},
+          stylesheets: {},
+          themes: {},
+          scripts: {},
+        },
+        'docusaurus.config.js',
+      ),
     ).toThrowErrorMatchingSnapshot();
   });
 });
diff --git a/packages/docusaurus/src/server/config.ts b/packages/docusaurus/src/server/config.ts
index 84b4975f1249..6287b63ce3c1 100644
--- a/packages/docusaurus/src/server/config.ts
+++ b/packages/docusaurus/src/server/config.ts
@@ -8,10 +8,28 @@
 import path from 'path';
 import fs from 'fs-extra';
 import importFresh from 'import-fresh';
-import {DEFAULT_CONFIG_FILE_NAME} from '@docusaurus/utils';
+import logger from '@docusaurus/logger';
+import {DEFAULT_CONFIG_FILE_NAME, findAsyncSequential} from '@docusaurus/utils';
 import type {LoadContext} from '@docusaurus/types';
 import {validateConfig} from './configValidation';
 
+async function findConfig(siteDir: string) {
+  // We could support .mjs, .ts, etc. in the future
+  const candidates = ['.js', 'cjs'].map(
+    (ext) => DEFAULT_CONFIG_FILE_NAME + ext,
+  );
+  const configPath = await findAsyncSequential(
+    candidates.map((file) => path.join(siteDir, file)),
+    fs.pathExists,
+  );
+  if (!configPath) {
+    logger.error('No config file found.');
+    logger.info`Expected one of:${candidates}You can provide a custom config path with the code=${'--config'} option.`;
+    throw new Error();
+  }
+  return configPath;
+}
+
 export async function loadSiteConfig({
   siteDir,
   customConfigFilePath,
@@ -19,10 +37,9 @@ export async function loadSiteConfig({
   siteDir: string;
   customConfigFilePath?: string;
 }): Promise<Pick<LoadContext, 'siteConfig' | 'siteConfigPath'>> {
-  const siteConfigPath = path.resolve(
-    siteDir,
-    customConfigFilePath ?? DEFAULT_CONFIG_FILE_NAME,
-  );
+  const siteConfigPath = customConfigFilePath
+    ? path.resolve(siteDir, customConfigFilePath)
+    : await findConfig(siteDir);
 
   if (!(await fs.pathExists(siteConfigPath))) {
     throw new Error(`Config file at "${siteConfigPath}" not found.`);
@@ -35,6 +52,9 @@ export async function loadSiteConfig({
       ? await importedConfig()
       : await importedConfig;
 
-  const siteConfig = validateConfig(loadedConfig);
+  const siteConfig = validateConfig(
+    loadedConfig,
+    path.relative(siteDir, siteConfigPath),
+  );
   return {siteConfig, siteConfigPath};
 }
diff --git a/packages/docusaurus/src/server/configValidation.ts b/packages/docusaurus/src/server/configValidation.ts
index f8a0985903a8..de94161306cd 100644
--- a/packages/docusaurus/src/server/configValidation.ts
+++ b/packages/docusaurus/src/server/configValidation.ts
@@ -6,10 +6,7 @@
  */
 
 import type {DocusaurusConfig, I18nConfig} from '@docusaurus/types';
-import {
-  DEFAULT_CONFIG_FILE_NAME,
-  DEFAULT_STATIC_DIR_NAME,
-} from '@docusaurus/utils';
+import {DEFAULT_STATIC_DIR_NAME} from '@docusaurus/utils';
 import {Joi, URISchema, printWarning} from '@docusaurus/utils-validation';
 
 const DEFAULT_I18N_LOCALE = 'en';
@@ -239,6 +236,7 @@ export const ConfigSchema = Joi.object({
 // TODO move to @docusaurus/utils-validation
 export function validateConfig(
   config: Partial<DocusaurusConfig>,
+  siteConfigPath: string,
 ): DocusaurusConfig {
   const {error, warning, value} = ConfigSchema.validate(config, {
     abortEarly: false,
@@ -261,7 +259,7 @@ export function validateConfig(
       '',
     );
     formattedError = unknownFields
-      ? `${formattedError}These field(s) (${unknownFields}) are not recognized in ${DEFAULT_CONFIG_FILE_NAME}.\nIf you still want these fields to be in your configuration, put them in the "customFields" field.\nSee https://docusaurus.io/docs/api/docusaurus-config/#customfields`
+      ? `${formattedError}These field(s) (${unknownFields}) are not recognized in ${siteConfigPath}.\nIf you still want these fields to be in your configuration, put them in the "customFields" field.\nSee https://docusaurus.io/docs/api/docusaurus-config/#customfields`
       : formattedError;
     throw new Error(formattedError);
   } else {