diff --git a/README.md b/README.md
index e77a5c1..fa6114f 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,7 @@ This library contains the following decorators
 | IsNumber   | numbers                       |
 | IsObject   | typed plain js objects        |
 | IsString   | strings                       |
+| IsUnknown  | any json value                |
 
 All of the decorators support the following parameters:
 
diff --git a/src/decorators/is-unknown.spec.ts b/src/decorators/is-unknown.spec.ts
new file mode 100644
index 0000000..b2bcd2f
--- /dev/null
+++ b/src/decorators/is-unknown.spec.ts
@@ -0,0 +1,66 @@
+import { Result } from 'true-myth';
+
+import { generateSchemas, input, make, output } from '../../tests/helpers';
+import { IsUnknown } from '../nestjs-swagger-dto';
+
+describe('IsUnknown', () => {
+  describe('single', () => {
+    class Test {
+      @IsUnknown()
+      unknownField!: unknown;
+    }
+
+    it('generates correct schema', async () => {
+      expect(await generateSchemas([Test])).toStrictEqual({
+        Test: {
+          type: 'object',
+          properties: {
+            unknownField: {
+              oneOf: [
+                { type: 'string' },
+                { type: 'number' },
+                { type: 'integer' },
+                { type: 'boolean' },
+                { type: 'array' },
+                { type: 'object' },
+              ],
+            },
+          },
+          required: ['unknownField'],
+        },
+      });
+    });
+
+    it('accepts anything except null and undefined', async () => {
+      expect(await input(Test, { unknownField: false })).toStrictEqual(
+        Result.ok(make(Test, { unknownField: false }))
+      );
+      expect(await input(Test, { unknownField: 123 })).toStrictEqual(
+        Result.ok(make(Test, { unknownField: 123 }))
+      );
+      expect(await input(Test, { unknownField: 'abc' })).toStrictEqual(
+        Result.ok(make(Test, { unknownField: 'abc' }))
+      );
+      expect(await input(Test, { unknownField: [] })).toStrictEqual(
+        Result.ok(make(Test, { unknownField: [] }))
+      );
+      expect(await input(Test, { unknownField: {} })).toStrictEqual(
+        Result.ok(make(Test, { unknownField: {} }))
+      );
+    });
+
+    it('transforms to plain', async () => {
+      const dto = make(Test, { unknownField: true });
+      expect(output(dto)).toStrictEqual({ unknownField: true });
+    });
+
+    it('rejects null and undefined by default', async () => {
+      expect(await input(Test, { unknownField: null })).toStrictEqual(
+        Result.err('unknownField should not be null or undefined')
+      );
+      expect(await input(Test, {})).toStrictEqual(
+        Result.err('unknownField should not be null or undefined')
+      );
+    });
+  });
+});
diff --git a/src/decorators/is-unknown.ts b/src/decorators/is-unknown.ts
new file mode 100644
index 0000000..26aa872
--- /dev/null
+++ b/src/decorators/is-unknown.ts
@@ -0,0 +1,24 @@
+import { IsDefined } from 'class-validator';
+
+import { BasePropertyOptions, compose } from '../core';
+
+export const IsUnknown = ({
+  ...base
+}: BasePropertyOptions & {
+  example?: unknown;
+  default?: unknown;
+} = {}): PropertyDecorator =>
+  compose(
+    {
+      oneOf: [
+        { type: 'string' },
+        { type: 'number' },
+        { type: 'integer' },
+        { type: 'boolean' },
+        { type: 'array' },
+        { type: 'object' },
+      ],
+    },
+    base,
+    IsDefined()
+  );
diff --git a/src/nestjs-swagger-dto.ts b/src/nestjs-swagger-dto.ts
index ac1c604..63bd07b 100644
--- a/src/nestjs-swagger-dto.ts
+++ b/src/nestjs-swagger-dto.ts
@@ -12,4 +12,5 @@ export * from './decorators/is-nested';
 export * from './decorators/is-number';
 export * from './decorators/is-object';
 export * from './decorators/is-string';
+export * from './decorators/is-unknown';
 export * from './decorators/typed-headers.decorator';