diff --git a/packages/docusaurus-theme-search-algolia/package.json b/packages/docusaurus-theme-search-algolia/package.json
index 2ae636ca55..ba0db4ccd2 100644
--- a/packages/docusaurus-theme-search-algolia/package.json
+++ b/packages/docusaurus-theme-search-algolia/package.json
@@ -9,6 +9,7 @@
   "license": "MIT",
   "dependencies": {
     "@docsearch/react": "^1.0.0-alpha.24",
+    "@hapi/joi": "^17.1.1",
     "algoliasearch": "^4.0.0",
     "algoliasearch-helper": "^3.1.1",
     "clsx": "^1.1.1",
diff --git a/packages/docusaurus-theme-search-algolia/src/__tests__/validateThemeConfig.test.js b/packages/docusaurus-theme-search-algolia/src/__tests__/validateThemeConfig.test.js
new file mode 100644
index 0000000000..cb842e8233
--- /dev/null
+++ b/packages/docusaurus-theme-search-algolia/src/__tests__/validateThemeConfig.test.js
@@ -0,0 +1,91 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const {validateThemeConfig, DEFAULT_CONFIG} = require('../validateThemeConfig');
+
+function testValidateThemeConfig(themeConfig) {
+  function validate(schema, cfg) {
+    const {value, error} = schema.validate(cfg, {
+      convert: false,
+    });
+    if (error) {
+      throw error;
+    }
+    return value;
+  }
+
+  return validateThemeConfig({themeConfig, validate});
+}
+
+describe('validateThemeConfig', () => {
+  test('minimal config', () => {
+    const algolia = {
+      indexName: 'index',
+      apiKey: 'apiKey',
+    };
+    expect(testValidateThemeConfig({algolia})).toEqual({
+      algolia: {
+        ...DEFAULT_CONFIG,
+        ...algolia,
+      },
+    });
+  });
+
+  test('unknown attributes', () => {
+    const algolia = {
+      indexName: 'index',
+      apiKey: 'apiKey',
+      unknownKey: 'unknownKey',
+    };
+    expect(testValidateThemeConfig({algolia})).toEqual({
+      algolia: {
+        ...DEFAULT_CONFIG,
+        ...algolia,
+      },
+    });
+  });
+
+  test('undefined config', () => {
+    const algolia = undefined;
+    expect(() =>
+      testValidateThemeConfig({algolia}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"\\"themeConfig.algolia\\" is required"`,
+    );
+  });
+
+  test('undefined config 2', () => {
+    expect(() =>
+      testValidateThemeConfig({}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"\\"themeConfig.algolia\\" is required"`,
+    );
+  });
+
+  test('empty config', () => {
+    const algolia = {};
+    expect(() =>
+      testValidateThemeConfig({algolia}),
+    ).toThrowErrorMatchingInlineSnapshot(`"\\"algolia.apiKey\\" is required"`);
+  });
+
+  test('missing indexName config', () => {
+    const algolia = {apiKey: 'apiKey'};
+    expect(() =>
+      testValidateThemeConfig({algolia}),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"\\"algolia.indexName\\" is required"`,
+    );
+  });
+
+  test('missing apiKey config', () => {
+    const algolia = {indexName: 'indexName'};
+    expect(() =>
+      testValidateThemeConfig({algolia}),
+    ).toThrowErrorMatchingInlineSnapshot(`"\\"algolia.apiKey\\" is required"`);
+  });
+});
diff --git a/packages/docusaurus-theme-search-algolia/src/index.js b/packages/docusaurus-theme-search-algolia/src/index.js
index 634108bded..958c0d6f81 100644
--- a/packages/docusaurus-theme-search-algolia/src/index.js
+++ b/packages/docusaurus-theme-search-algolia/src/index.js
@@ -10,10 +10,11 @@ const fs = require('fs');
 const eta = require('eta');
 const {normalizeUrl} = require('@docusaurus/utils');
 const openSearchTemplate = require('./templates/opensearch');
+const {validateThemeConfig} = require('./validateThemeConfig');
 
 const OPEN_SEARCH_FILENAME = 'opensearch.xml';
 
-module.exports = function (context) {
+function theme(context) {
   const {
     baseUrl,
     siteConfig: {title, url, favicon},
@@ -70,4 +71,8 @@ module.exports = function (context) {
       };
     },
   };
-};
+}
+
+module.exports = theme;
+
+theme.validateThemeConfig = validateThemeConfig;
diff --git a/packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js b/packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js
index 7596f5ce13..3c0e3c8c1d 100644
--- a/packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js
+++ b/packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js
@@ -128,17 +128,7 @@ function DocSearch(props) {
 }
 
 function SearchBar() {
-  const {siteConfig = {}} = useDocusaurusContext();
-
-  if (!siteConfig.themeConfig.algolia) {
-    // eslint-disable-next-line no-console
-    console.warn(`DocSearch requires an \`algolia\` field in your \`themeConfig\`.
-
-See: https://v2.docusaurus.io/docs/search/#using-algolia-docsearch`);
-
-    return null;
-  }
-
+  const {siteConfig} = useDocusaurusContext();
   return <DocSearch {...siteConfig.themeConfig.algolia} />;
 }
 
diff --git a/packages/docusaurus-theme-search-algolia/src/validateThemeConfig.js b/packages/docusaurus-theme-search-algolia/src/validateThemeConfig.js
new file mode 100644
index 0000000000..adda5956c5
--- /dev/null
+++ b/packages/docusaurus-theme-search-algolia/src/validateThemeConfig.js
@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const Joi = require('@hapi/joi');
+
+const DEFAULT_CONFIG = {
+  // By default, all Docusaurus sites are using the same AppId
+  // This has been designed on purpose with Algolia.
+  appId: 'BH4D9OD16A',
+};
+exports.DEFAULT_CONFIG = DEFAULT_CONFIG;
+
+const Schema = Joi.object({
+  algolia: Joi.object({
+    appId: Joi.string().default(DEFAULT_CONFIG.appId),
+    apiKey: Joi.string().required(),
+    indexName: Joi.string().required(),
+  })
+    .label('themeConfig.algolia')
+    .required()
+    .unknown(), // DocSearch 3 is still alpha: don't validate the rest for now
+});
+exports.Schema = Schema;
+
+exports.validateThemeConfig = function validateThemeConfig({
+  validate,
+  themeConfig,
+}) {
+  return validate(Schema, themeConfig);
+};