diff --git a/packages/docusaurus-utils-validation/src/validationUtils.ts b/packages/docusaurus-utils-validation/src/validationUtils.ts
index 7b20ce7244..3c15dbb125 100644
--- a/packages/docusaurus-utils-validation/src/validationUtils.ts
+++ b/packages/docusaurus-utils-validation/src/validationUtils.ts
@@ -35,7 +35,7 @@ export const logValidationBugReportHint = (): void => {
   );
 };
 
-function printWarning(warning?: Joi.ValidationError) {
+export function printWarning(warning?: Joi.ValidationError) {
   if (warning) {
     const warningMessages = warning.details
       .map(({message}) => message)
diff --git a/packages/docusaurus/src/server/__tests__/configValidation.test.ts b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
index bc4a633e65..acd4e24650 100644
--- a/packages/docusaurus/src/server/__tests__/configValidation.test.ts
+++ b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {DEFAULT_CONFIG, validateConfig} from '../configValidation';
+import {
+  ConfigSchema,
+  DEFAULT_CONFIG,
+  validateConfig,
+} from '../configValidation';
 import {DocusaurusConfig} from '@docusaurus/types';
 
 const baseConfig = {
@@ -197,3 +201,26 @@ describe('normalizeConfig', () => {
     ).toThrowErrorMatchingSnapshot();
   });
 });
+
+describe('config warnings', () => {
+  function getWarning(config: unknown) {
+    return ConfigSchema.validate(config).warning;
+  }
+
+  test('baseConfig has no warning', () => {
+    const warning = getWarning(baseConfig);
+    expect(warning).toBeUndefined();
+  });
+
+  test('site url has warning when using subpath', () => {
+    const warning = getWarning({
+      ...baseConfig,
+      url: 'https://mysite.com/someSubpath',
+    });
+    expect(warning).toBeDefined();
+    expect(warning?.details.length).toEqual(1);
+    expect(warning?.details[0].message).toMatchInlineSnapshot(
+      `"Docusaurus config validation warning. Field \\"url\\": the url is not supposed to contain a sub-path like '/someSubpath', please use the baseUrl field for sub-paths"`,
+    );
+  });
+});
diff --git a/packages/docusaurus/src/server/configValidation.ts b/packages/docusaurus/src/server/configValidation.ts
index 66f1e842cf..673c130f87 100644
--- a/packages/docusaurus/src/server/configValidation.ts
+++ b/packages/docusaurus/src/server/configValidation.ts
@@ -12,6 +12,7 @@ import {
   logValidationBugReportHint,
   isValidationDisabledEscapeHatch,
   URISchema,
+  printWarning,
 } from '@docusaurus/utils-validation';
 
 const DEFAULT_I18N_LOCALE = 'en';
@@ -107,8 +108,20 @@ const I18N_CONFIG_SCHEMA = Joi.object<I18nConfig>({
   .optional()
   .default(DEFAULT_I18N_CONFIG);
 
+const SiteUrlSchema = URISchema.required().custom(function (value, helpers) {
+  try {
+    const {pathname} = new URL(value);
+    if (pathname !== '/') {
+      helpers.warn('docusaurus.configValidationWarning', {
+        warningMessage: `the url is not supposed to contain a sub-path like '${pathname}', please use the baseUrl field for sub-paths`,
+      });
+    }
+  } catch (e) {}
+  return value;
+}, 'siteUrlCustomValidation');
+
 // TODO move to @docusaurus/utils-validation
-const ConfigSchema = Joi.object({
+export const ConfigSchema = Joi.object({
   baseUrl: Joi.string()
     .required()
     .regex(new RegExp('/$', 'm'))
@@ -116,7 +129,7 @@ const ConfigSchema = Joi.object({
   baseUrlIssueBanner: Joi.boolean().default(DEFAULT_CONFIG.baseUrlIssueBanner),
   favicon: Joi.string().required(),
   title: Joi.string().required(),
-  url: URISchema.required(),
+  url: SiteUrlSchema,
   trailingSlash: Joi.boolean(), // No default value! undefined = retrocompatible legacy behavior!
   i18n: I18N_CONFIG_SCHEMA,
   onBrokenLinks: Joi.string()
@@ -163,15 +176,21 @@ const ConfigSchema = Joi.object({
       .try(Joi.string().equal('babel'), Joi.function())
       .optional(),
   }).optional(),
+}).messages({
+  'docusaurus.configValidationWarning':
+    'Docusaurus config validation warning. Field {#label}: {#warningMessage}',
 });
 
 // TODO move to @docusaurus/utils-validation
 export function validateConfig(
   config: Partial<DocusaurusConfig>,
 ): DocusaurusConfig {
-  const {error, value} = ConfigSchema.validate(config, {
+  const {error, warning, value} = ConfigSchema.validate(config, {
     abortEarly: false,
   });
+
+  printWarning(warning);
+
   if (error) {
     logValidationBugReportHint();
     if (isValidationDisabledEscapeHatch) {