diff --git a/Validator.test.ts b/Validator.test.ts
index c962f85..3cad67c 100644
--- a/Validator.test.ts
+++ b/Validator.test.ts
@@ -9,6 +9,7 @@ import {
   isString,
   isNumber,
   isInteger,
+  isRequired,
 } from "./mod.ts";
 
 Deno.test("validate schema (match)", async () => {
@@ -17,6 +18,11 @@ Deno.test("validate schema (match)", async () => {
     ["string", [isString]],
     [["arr", "ay"], { [ArraySymbol]: isString }],
     [{ foo: 3.1415, lorem: "ipsum" }, { foo: isNumber, lorem: [isString] }],
+    [{}, { optional: [isString] }],
+    [{ foo: { bar: "" } }, { foo: { bar: [isRequired, isString] } }],
+    [{ foo: { bar: "" } }, { foo: { bar: [isString] } }],
+    [{ foo: {} }, { foo: { bar: [isString] } }],
+    [{}, { foo: { bar: [isString] } }],
   ];
   for (const [value, constraints] of values) {
     assertEquals([], await validate(value, constraints));
@@ -29,6 +35,10 @@ Deno.test("validate schema (no match)", async () => {
     [false, [isString]],
     [["arr", ["ay"]], { [ArraySymbol]: isString }],
     [{ foo: 3.1415, lorem: "ipsum" }, { foo: isInteger, lorem: [isString] }],
+    [{}, { required: [isRequired, isString] }],
+    [{ foo: { bar: 1 } }, { foo: { bar: [isRequired, isString] } }],
+    [{ foo: {} }, { foo: { bar: [isRequired, isString] } }],
+    [{}, { foo: { bar: [isRequired, isString] } }],
   ];
   for (const [value, constraints] of values) {
     assertNotEquals([], await validate(value, constraints));
diff --git a/Validator.ts b/Validator.ts
index 35a786f..9a65feb 100644
--- a/Validator.ts
+++ b/Validator.ts
@@ -99,17 +99,8 @@ async function validateSchema(
     if (!validators.hasOwnProperty(prop)) {
       continue;
     }
-    if (value.hasOwnProperty(prop)) {
-      const errors = await validate(value[prop], v[prop]);
-      valErrors.push(...(errors ?? []));
-    } else {
-      valErrors.push({
-        type: "property",
-        param: [prop],
-        message: `Property '${prop}' expected but not found!`,
-        args: { property: prop },
-      });
-    }
+    const errors = await validate(value && value[prop], v[prop]);
+    valErrors.push(...(errors ?? []));
   }
   return valErrors;
 }
diff --git a/mod.ts b/mod.ts
index e1fd508..2f6dfc5 100644
--- a/mod.ts
+++ b/mod.ts
@@ -8,4 +8,8 @@ export {
 } from "./Validator.ts";
 export { isString } from "./validators/string.ts";
 export { isNumber, isInteger } from "./validators/number.ts";
+export { isArray } from "./validators/array.ts";
 export { or } from "./validators/logic.ts";
+export { isRequired, isDefined, isNotEmpty } from "./validators/empty.ts";
+export { isSymbol } from "./validators/symbol.ts";
+export { isBoolean } from "./validators/boolean.ts";
diff --git a/validators/array.test.ts b/validators/array.test.ts
new file mode 100644
index 0000000..e634f0b
--- /dev/null
+++ b/validators/array.test.ts
@@ -0,0 +1,38 @@
+import { isArray } from "./array.ts";
+import { validate } from "../mod.ts";
+import {
+  assertEquals,
+  assertNotEquals,
+} from "https://deno.land/std@0.53.0/testing/asserts.ts";
+
+Deno.test("isArray (match)", async () => {
+  const values = [
+    undefined,
+    null,
+    [],
+    ["foo"],
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isArray), []);
+  }
+});
+
+Deno.test("isArray (no match)", async () => {
+  const values = [
+    0,
+    1,
+    false,
+    true,
+    "",
+    "foo",
+    new String(),
+    new String("bar"),
+    () => {},
+    function named() {},
+    new Object(),
+    Symbol(),
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isArray), []);
+  }
+});
diff --git a/validators/array.ts b/validators/array.ts
new file mode 100644
index 0000000..e3db194
--- /dev/null
+++ b/validators/array.ts
@@ -0,0 +1,14 @@
+import { Validator, Args } from "../mod.ts";
+
+export const isArray: Validator = {
+  type: "isArray",
+  check: (value: any) => {
+    if (value === null || value === undefined) return;
+    if (!Array.isArray(value)) {
+      return {};
+    }
+  },
+  message: (value: any, args?: Args) => {
+    return `This value has to be an array.`;
+  },
+};
diff --git a/validators/boolean.test.ts b/validators/boolean.test.ts
new file mode 100644
index 0000000..48725d7
--- /dev/null
+++ b/validators/boolean.test.ts
@@ -0,0 +1,36 @@
+import { isBoolean } from "./boolean.ts";
+import { validate } from "../mod.ts";
+import {
+  assertEquals,
+  assertNotEquals,
+} from "https://deno.land/std@0.53.0/testing/asserts.ts";
+
+Deno.test("isBoolean (match)", async () => {
+  const values = [
+    undefined,
+    null,
+    true,
+    false,
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isBoolean), []);
+  }
+});
+
+Deno.test("isBoolean (no match)", async () => {
+  const values = [
+    0,
+    1,
+    "",
+    "foo",
+    new String(),
+    new String("bar"),
+    () => {},
+    function named() {},
+    new Object(),
+    Symbol(),
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isBoolean), []);
+  }
+});
diff --git a/validators/boolean.ts b/validators/boolean.ts
new file mode 100644
index 0000000..d9c787a
--- /dev/null
+++ b/validators/boolean.ts
@@ -0,0 +1,14 @@
+import { Validator, Args } from "../mod.ts";
+
+export const isBoolean: Validator = {
+  type: "isBoolean",
+  check: (value: any) => {
+    if (value === null || value === undefined) return;
+    if (value !== true && value !== false) {
+      return {};
+    }
+  },
+  message: (value: any, args?: Args) => {
+    return `This value has to be a boolean.`;
+  },
+};
diff --git a/validators/empty.test.ts b/validators/empty.test.ts
new file mode 100644
index 0000000..9d39139
--- /dev/null
+++ b/validators/empty.test.ts
@@ -0,0 +1,99 @@
+import { isRequired, isDefined, isNotEmpty } from "./empty.ts";
+import { validate } from "../mod.ts";
+import {
+  assertEquals,
+  assertNotEquals,
+} from "https://deno.land/std@0.53.0/testing/asserts.ts";
+
+Deno.test("isRequired (match)", async () => {
+  const values = [
+    "",
+    "  ",
+    "foo",
+    0,
+    1,
+    true,
+    false,
+    NaN,
+    {},
+    { foo: "bar" },
+    [],
+    ["foo"],
+    Symbol("foo"),
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isRequired), []);
+  }
+});
+
+Deno.test("isRequired (no match)", async () => {
+  const values = [
+    undefined,
+    null,
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isRequired), []);
+  }
+});
+
+Deno.test("isDefined (match)", async () => {
+  const values = [
+    null,
+    "",
+    "  ",
+    "foo",
+    0,
+    1,
+    true,
+    false,
+    NaN,
+    {},
+    { foo: "bar" },
+    [],
+    ["foo"],
+    Symbol("foo"),
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isDefined), []);
+  }
+});
+
+Deno.test("isDefined (no match)", async () => {
+  const values = [
+    undefined,
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isDefined), []);
+  }
+});
+
+Deno.test("isNotEmpty (match)", async () => {
+  const values = [
+    "foo",
+    0,
+    1,
+    true,
+    false,
+    NaN,
+    { foo: "bar" },
+    ["foo"],
+    Symbol("foo"),
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isNotEmpty), []);
+  }
+});
+
+Deno.test("isNotEmpty (no match)", async () => {
+  const values = [
+    undefined,
+    null,
+    "",
+    "  ",
+    {},
+    [],
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isNotEmpty), []);
+  }
+});
diff --git a/validators/empty.ts b/validators/empty.ts
new file mode 100644
index 0000000..b477974
--- /dev/null
+++ b/validators/empty.ts
@@ -0,0 +1,70 @@
+import {
+  Validator,
+  Args,
+  isString,
+  isArray,
+  isNumber,
+  isSymbol,
+  isBoolean,
+} from "../mod.ts";
+
+export const isRequired: Validator = {
+  type: "isRequired",
+  check: (value: any) => {
+    if (value === null || value === undefined) {
+      return {};
+    }
+  },
+  message: (value: any, args?: Args) => {
+    return `This value is required.`;
+  },
+};
+
+export const isDefined: Validator = {
+  type: "isDefined",
+  check: (value: any) => {
+    if (value === undefined) {
+      return {};
+    }
+  },
+  message: (value: any, args?: Args) => {
+    return `This value has to be defined.`;
+  },
+};
+
+export const isNotEmpty: Validator = {
+  type: "isNotEmpty",
+  check: async (value: any) => {
+    if (value === null || value === undefined) {
+      return {};
+    }
+    if ((await isString.check(value)) === undefined) {
+      if (/^\s*$/.test(value)) {
+        return {};
+      }
+      return;
+    }
+    if ((await isNumber.check(value)) === undefined || Number.isNaN(value)) {
+      return;
+    }
+    if (await isSymbol.check(value) === undefined) {
+      return;
+    }
+    if (await isBoolean.check(value) === undefined) {
+      return;
+    }
+    if ((await isArray.check(value)) === undefined) {
+      if (value.length > 0) {
+        return;
+      }
+      return {};
+    }
+    for (const key in value) {
+      return;
+    }
+    return {};
+  },
+  message: (value: any, args?: Args) => {
+    return `This value has to be non-empty.`;
+  },
+};
diff --git a/validators/number.ts b/validators/number.ts
index c53acaf..6fb7c0b 100644
--- a/validators/number.ts
+++ b/validators/number.ts
@@ -9,7 +9,7 @@ export const isNumber: Validator = {
     }
   },
   message: (value: any, args?: Args) => {
-    return `The value '${value && value.toString()}' has to be a number.`;
+    return `This value has to be a number.`;
   },
 };
 
@@ -22,6 +22,6 @@ export const isInteger: Validator = {
     }
   },
   message: (value: any, args?: Args) => {
-    return `The value '${value && value.toString()}' has to be an integer.`;
+    return `This value has to be an integer.`;
   },
 };
diff --git a/validators/string.ts b/validators/string.ts
index 3d84c3d..f26a85e 100644
--- a/validators/string.ts
+++ b/validators/string.ts
@@ -9,6 +9,6 @@ export const isString: Validator = {
     }
   },
   message: (value: any, args?: Args) => {
-    return `The value '${value && value.toString()}' has to be a string.`;
+    return `This value has to be a string.`;
   },
 };
diff --git a/validators/symbol.test.ts b/validators/symbol.test.ts
new file mode 100644
index 0000000..bfd309e
--- /dev/null
+++ b/validators/symbol.test.ts
@@ -0,0 +1,36 @@
+import { isSymbol } from "./symbol.ts";
+import { validate } from "../mod.ts";
+import {
+  assertEquals,
+  assertNotEquals,
+} from "https://deno.land/std@0.53.0/testing/asserts.ts";
+
+Deno.test("isSymbol (match)", async () => {
+  const values = [
+    undefined,
+    null,
+    Symbol(),
+  ];
+  for (const value of values) {
+    assertEquals(await validate(value, isSymbol), []);
+  }
+});
+
+Deno.test("isSymbol (no match)", async () => {
+  const values = [
+    0,
+    1,
+    true,
+    false,
+    "",
+    "foo",
+    new String(),
+    new String("bar"),
+    () => {},
+    function named() {},
+    new Object(),
+  ];
+  for (const value of values) {
+    assertNotEquals(await validate(value, isSymbol), []);
+  }
+});
diff --git a/validators/symbol.ts b/validators/symbol.ts
new file mode 100644
index 0000000..35b80db
--- /dev/null
+++ b/validators/symbol.ts
@@ -0,0 +1,14 @@
+import { Validator, Args } from "../mod.ts";
+
+export const isSymbol: Validator = {
+  type: "isSymbol",
+  check: (value: any) => {
+    if (value === null || value === undefined) return;
+    if (typeof value !== "symbol") {
+      return {};
+    }
+  },
+  message: (value: any, args?: Args) => {
+    return `This value has to be a symbol.`;
+  },
+};