diff --git a/packages/plugin-manifest-validator/README.md b/packages/plugin-manifest-validator/README.md
index 2fad1cb6dd..9acd81e80c 100644
--- a/packages/plugin-manifest-validator/README.md
+++ b/packages/plugin-manifest-validator/README.md
@@ -27,11 +27,11 @@ console.log(result.valid); // true or false
 console.log(result.errors); // array of ajv error objects
 ```
 
-[ajv error objects](https://github.com/epoberezkin/ajv#validation-errors) is like:
+[ajv error objects](https://ajv.js.org/docs/api.html#validation-errors) is like:
 
 ```js
 {
-  dataPath: '.version',
+  dataPath: '/version',
   keyword: 'type',
   message: 'should be integer',
   params: {
diff --git a/packages/plugin-manifest-validator/manifest-schema.d.ts b/packages/plugin-manifest-validator/manifest-schema.d.ts
index 00c42f8815..e2cd4eafce 100644
--- a/packages/plugin-manifest-validator/manifest-schema.d.ts
+++ b/packages/plugin-manifest-validator/manifest-schema.d.ts
@@ -5,7 +5,414 @@
  * and run json-schema-to-typescript to regenerate this file.
  */
 
-export type Resources = string[];
+export type Resources =
+  | []
+  | [string]
+  | [string, string]
+  | [string, string, string]
+  | [string, string, string, string]
+  | [string, string, string, string, string]
+  | [string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string, string, string, string, string]
+  | [string, string, string, string, string, string, string, string, string, string, string, string, string, string]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ]
+  | [
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string,
+      string
+    ];
 
 export interface KintonePluginManifestJson {
   manifest_version: number;
diff --git a/packages/plugin-manifest-validator/manifest-schema.json b/packages/plugin-manifest-validator/manifest-schema.json
index 9c48ac4e25..cf9a801119 100644
--- a/packages/plugin-manifest-validator/manifest-schema.json
+++ b/packages/plugin-manifest-validator/manifest-schema.json
@@ -163,9 +163,9 @@
         }, {
           "format": "relative-path",
           "maxFileSize": "20MB"
-        }],
-        "maxItems": 30
-      }
+        }]
+      },
+      "maxItems": 30
     }
   }
 }
diff --git a/packages/plugin-manifest-validator/package.json b/packages/plugin-manifest-validator/package.json
index 0a3bf0d094..9020f92392 100644
--- a/packages/plugin-manifest-validator/package.json
+++ b/packages/plugin-manifest-validator/package.json
@@ -24,7 +24,7 @@
     "clean": "rimraf dist"
   },
   "dependencies": {
-    "ajv": "^6.12.6",
+    "ajv": "^7.0.3",
     "bytes": "^3.1.0"
   },
   "devDependencies": {
diff --git a/packages/plugin-manifest-validator/src/__tests__/index.ts b/packages/plugin-manifest-validator/src/__tests__/index.ts
index 27e0ea2306..2cb9c5e3d0 100644
--- a/packages/plugin-manifest-validator/src/__tests__/index.ts
+++ b/packages/plugin-manifest-validator/src/__tests__/index.ts
@@ -22,9 +22,9 @@ describe("validator", () => {
       valid: false,
       errors: [
         {
-          dataPath: ".version",
+          dataPath: "",
           keyword: "required",
-          message: "is a required property",
+          message: "should have required property 'version'",
           params: {
             missingProperty: "version",
           },
@@ -39,7 +39,7 @@ describe("validator", () => {
       valid: false,
       errors: [
         {
-          dataPath: ".version",
+          dataPath: "/version",
           keyword: "type",
           message: "should be integer",
           params: {
@@ -56,12 +56,11 @@ describe("validator", () => {
       valid: false,
       errors: [
         {
-          dataPath: ".version",
+          dataPath: "/version",
           keyword: "minimum",
           message: "should be >= 1",
           params: {
             comparison: ">=",
-            exclusive: false,
             limit: 1,
           },
           schemaPath: "#/properties/version/minimum",
@@ -75,7 +74,7 @@ describe("validator", () => {
       valid: false,
       errors: [
         {
-          dataPath: ".type",
+          dataPath: "/type",
           keyword: "enum",
           message: "should be equal to one of the allowed values",
           params: {
@@ -92,9 +91,9 @@ describe("validator", () => {
       valid: false,
       errors: [
         {
-          dataPath: ".description.en",
+          dataPath: "/description",
           keyword: "required",
-          message: "is a required property",
+          message: "should have required property 'en'",
           params: {
             missingProperty: "en",
           },
@@ -164,7 +163,7 @@ describe("validator", () => {
       assert(actual.valid === false);
       assert(actual.errors?.length === 1);
       assert.deepStrictEqual(actual.errors[0], {
-        dataPath: ".icon",
+        dataPath: "/icon",
         keyword: "maxFileSize",
         message: "file size should be <= 20MB",
         params: {
@@ -190,7 +189,7 @@ describe("validator", () => {
       assert(actual.valid === false);
       assert(actual.errors?.length === 3);
       assert.deepStrictEqual(actual.errors[1], {
-        dataPath: ".desktop.js[0]",
+        dataPath: "/desktop/js/0",
         keyword: "maxFileSize",
         message: "file size should be <= 20MB",
         params: {
@@ -216,7 +215,7 @@ describe("validator", () => {
       assert(actual.valid === false);
       assert(actual.errors?.length === 3);
       assert.deepStrictEqual(actual.errors[1], {
-        dataPath: ".desktop.css[0]",
+        dataPath: "/desktop/css/0",
         keyword: "maxFileSize",
         message: "file size should be <= 20MB",
         params: {
@@ -239,6 +238,31 @@ describe("validator", () => {
       assert(actual.errors === null);
     });
   });
+  describe("maxItems", () => {
+    it("exceed the max item counts", () => {
+      const urls = [...new Array(100)].map(
+        (_, i) => `https://example.com/${i}.js`
+      );
+      const actual = validator(
+        json({
+          desktop: {
+            js: urls,
+          },
+        })
+      );
+      assert.strictEqual(actual.valid, false);
+      assert.strictEqual(actual.errors?.length, 1);
+      assert.deepStrictEqual(actual.errors[0], {
+        dataPath: "/desktop/js",
+        keyword: "maxItems",
+        message: "should NOT have more than 30 items",
+        params: {
+          limit: 30,
+        },
+        schemaPath: "#/definitions/resources/maxItems",
+      });
+    });
+  });
 });
 
 /**
diff --git a/packages/plugin-manifest-validator/src/index.ts b/packages/plugin-manifest-validator/src/index.ts
index fb4124b09d..0fc2be26a5 100644
--- a/packages/plugin-manifest-validator/src/index.ts
+++ b/packages/plugin-manifest-validator/src/index.ts
@@ -1,15 +1,22 @@
 "use strict";
 
-import Ajv from "ajv";
+import Ajv, { ErrorObject } from "ajv";
 import bytes from "bytes";
 import jsonSchema from "../manifest-schema.json";
 import validateUrl from "./validate-https-url";
 
 type ValidateResult = {
   valid: boolean | PromiseLike<any>;
-  errors: null | Ajv.ErrorObject[];
+  errors: null | ErrorObject[];
 };
 
+// https://ajv.js.org/docs/keywords.html#define-keyword-with-validation-function
+// FIXME: use the type definition that Ajv provides if https://github.com/ajv-validator/ajv/pull/1460 has been merged
+interface SchemaValidateFunction {
+  (schema: string, data: string): boolean;
+  errors?: Array<Partial<ErrorObject>>;
+}
+
 /**
  * @param {Object} json
  * @param {Object=} options
@@ -27,10 +34,9 @@ export = function (
   if (typeof options.maxFileSize === "function") {
     maxFileSize = options.maxFileSize;
   }
+
   const ajv = new Ajv({
     allErrors: true,
-    unknownFormats: true,
-    errorDataPath: "property",
     formats: {
       "http-url": (str: string) => validateUrl(str, true),
       "https-url": (str: string) => validateUrl(str),
@@ -38,14 +44,7 @@ export = function (
     },
   });
 
-  ajv.removeKeyword("propertyNames");
-  ajv.removeKeyword("contains");
-  ajv.removeKeyword("const");
-  ajv.removeKeyword("if");
-  ajv.removeKeyword("then");
-  ajv.removeKeyword("else");
-
-  const validateMaxFileSize: Ajv.SchemaValidateFunction = (
+  const validateMaxFileSize: SchemaValidateFunction = (
     schema: string,
     data: string
   ) => {
@@ -55,7 +54,6 @@ export = function (
     const valid = maxFileSize(maxBytes, data);
     if (!valid) {
       validateMaxFileSize.errors = [
-        // @ts-expect-error TODO: Ajv.ErrorObject has need fixing.
         {
           keyword: "maxFileSize",
           params: {
@@ -68,7 +66,8 @@ export = function (
     return valid;
   };
 
-  ajv.addKeyword("maxFileSize", {
+  ajv.addKeyword({
+    keyword: "maxFileSize",
     validate: validateMaxFileSize,
   });
 
@@ -82,8 +81,8 @@ export = function (
  * @return {null|Array<Object>} shallow copy of the input or null
  */
 function transformErrors(
-  errors: undefined | null | Ajv.ErrorObject[]
-): null | Ajv.ErrorObject[] {
+  errors: undefined | null | ErrorObject[]
+): null | ErrorObject[] {
   if (!errors) {
     return null;
   }
diff --git a/packages/plugin-packer/test/packer.spec.ts b/packages/plugin-packer/test/packer.spec.ts
index 1325b819c0..38871735d1 100644
--- a/packages/plugin-packer/test/packer.spec.ts
+++ b/packages/plugin-packer/test/packer.spec.ts
@@ -84,9 +84,7 @@ describe("packer", () => {
     it("throws an error if the contents.zip is invalid", (done) => {
       const contentsZip = fs.readFileSync(invalidMaxFileSizeContentsZipPath);
       packer(contentsZip).catch((error) => {
-        expect(
-          error.message.indexOf('".icon" file size should be <= 20MB')
-        ).not.toBe(-1);
+        expect(error.message).toBe('"/icon" file size should be <= 20MB');
         done();
       });
     });
diff --git a/yarn.lock b/yarn.lock
index 2aa4404f25..5ce525941c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3043,7 +3043,7 @@ ajv@^6.1.0, ajv@^6.10.0, ajv@^6.12.3, ajv@^6.12.4, ajv@^6.12.5, ajv@^6.12.6:
     json-schema-traverse "^0.4.1"
     uri-js "^4.2.2"
 
-ajv@^7.0.2:
+ajv@^7.0.2, ajv@^7.0.3:
   version "7.0.3"
   resolved "https://registry.yarnpkg.com/ajv/-/ajv-7.0.3.tgz#13ae747eff125cafb230ac504b2406cf371eece2"
   integrity sha512-R50QRlXSxqXcQP5SvKUrw8VZeypvo12i2IX0EeR5PiZ7bEKeHWgzgo264LDadUsCU42lTJVhFikTqJwNeH34gQ==