diff --git a/library/src/actions/index.ts b/library/src/actions/index.ts
index 0c37dd5c..e38b4600 100644
--- a/library/src/actions/index.ts
+++ b/library/src/actions/index.ts
@@ -36,6 +36,7 @@ export * from './isoTime/index.ts';
 export * from './isoTimeSecond/index.ts';
 export * from './isoTimestamp/index.ts';
 export * from './isoWeek/index.ts';
+export * from './json/index.ts';
 export * from './length/index.ts';
 export * from './mac/index.ts';
 export * from './mac48/index.ts';
diff --git a/library/src/actions/json/index.ts b/library/src/actions/json/index.ts
new file mode 100644
index 00000000..de786e35
--- /dev/null
+++ b/library/src/actions/json/index.ts
@@ -0,0 +1 @@
+export * from './json.ts';
diff --git a/library/src/actions/json/json.test-d.ts b/library/src/actions/json/json.test-d.ts
new file mode 100644
index 00000000..8885229e
--- /dev/null
+++ b/library/src/actions/json/json.test-d.ts
@@ -0,0 +1,41 @@
+import { describe, expectTypeOf, test } from 'vitest';
+import type { InferInput, InferIssue, InferOutput } from '../../types/index.ts';
+import { json, type JsonAction, type JsonIssue } from './json.ts';
+
+describe('json', () => {
+  describe('should return action object', () => {
+    test('with undefined message', () => {
+      type Action = JsonAction<string, undefined>;
+      expectTypeOf(json<string>()).toEqualTypeOf<Action>();
+      expectTypeOf(json<string, undefined>(undefined)).toEqualTypeOf<Action>();
+    });
+
+    test('with string message', () => {
+      expectTypeOf(json<string, 'message'>('message')).toEqualTypeOf<
+        JsonAction<string, 'message'>
+      >();
+    });
+
+    test('with function message', () => {
+      expectTypeOf(json<string, () => string>(() => 'message')).toEqualTypeOf<
+        JsonAction<string, () => string>
+      >();
+    });
+  });
+
+  describe('should infer correct types', () => {
+    type Action = JsonAction<string, undefined>;
+
+    test('of input', () => {
+      expectTypeOf<InferInput<Action>>().toEqualTypeOf<string>();
+    });
+
+    test('of output', () => {
+      expectTypeOf<InferOutput<Action>>().toEqualTypeOf<string>();
+    });
+
+    test('of issue', () => {
+      expectTypeOf<InferIssue<Action>>().toEqualTypeOf<JsonIssue<string>>();
+    });
+  });
+});
diff --git a/library/src/actions/json/json.test.ts b/library/src/actions/json/json.test.ts
new file mode 100644
index 00000000..a1b742d3
--- /dev/null
+++ b/library/src/actions/json/json.test.ts
@@ -0,0 +1,139 @@
+import { describe, expect, test } from 'vitest';
+import { HEX_COLOR_REGEX } from '../../regex.ts';
+import type { StringIssue } from '../../schemas/index.ts';
+import { expectActionIssue, expectNoActionIssue } from '../../vitest/index.ts';
+import {
+  json,
+  type JsonAction,
+  type JsonIssue,
+} from './json.ts';
+
+describe('json', () => {
+  describe('should return action object', () => {
+    const baseAction: Omit<JsonAction<string, never>, 'message'> = {
+      kind: 'validation',
+      type: 'json',
+      reference: json,
+      expects: null,
+      requirement: expect.any(Function),
+      async: false,
+      '~run': expect.any(Function),
+    };
+
+    test('with undefined message', () => {
+      const action: JsonAction<string, undefined> = {
+        ...baseAction,
+        message: undefined,
+      };
+      expect(json()).toStrictEqual(action);
+      expect(json(undefined)).toStrictEqual(action);
+    });
+
+    test('with string message', () => {
+      expect(json('message')).toStrictEqual({
+        ...baseAction,
+        message: 'message',
+      } satisfies JsonAction<string, string>);
+    });
+
+    test('with function message', () => {
+      const message = () => 'message';
+      expect(json(message)).toStrictEqual({
+        ...baseAction,
+        message,
+      } satisfies JsonAction<string, typeof message>);
+    });
+  });
+
+  describe('should return dataset without issues', () => {
+    const action = json();
+
+    test('for untyped inputs', () => {
+      const issues: [StringIssue] = [
+        {
+          kind: 'schema',
+          type: 'string',
+          input: null,
+          expected: 'string',
+          received: 'null',
+          message: 'message',
+        },
+      ];
+      expect(
+        action['~run']({ typed: false, value: null, issues }, {})
+      ).toStrictEqual({
+        typed: false,
+        value: null,
+        issues,
+      });
+    });
+
+    test('for literals', () => {
+      expectNoActionIssue(action, [
+        '{}',
+        '[]',
+        'null',
+        '123',
+        '"example"',
+        '12.3',
+        '"escaped \\"quote"',
+      ]);
+    });
+
+    test('for complex values', () => {
+      expectNoActionIssue(action, [
+        '{"name":"John Doe","age":30,"color":null,"children":["Alice","Bob"]}',
+        '[123, "John Doe", null, {"fruit":"apple"}]',
+      ]);
+    });
+  });
+
+  describe('should return dataset with issues', () => {
+    const action = json('message');
+    const baseIssue: Omit<JsonIssue<string>, 'input' | 'received'> = {
+      kind: 'validation',
+      type: 'json',
+      expected: null,
+      message: 'message',
+      requirement: expect.any(Function),
+    };
+
+    test('for empty strings', () => {
+      expectActionIssue(action, baseIssue, ['', ' ', '\n']);
+    });
+
+    test('for malformed strings', () => {
+      expectActionIssue(action, baseIssue, [
+        '{"key:"value"}',
+        '{key":"value"}',
+        "'key'",
+        '"unescaped "quote""',
+        '{]',
+        '[}',
+      ]);
+    });
+
+    test('for malformed arrays', () => {
+      expectActionIssue(action, baseIssue, [
+        '[1, 2, , 3]',
+        '[1, 2, "key":"value"]',
+      ]);
+    });
+
+    test('for malformed objects', () => {
+      expectActionIssue(action, baseIssue, [
+        '{"key":"value",,"key2": "value2"}',
+        '{"key":"value","key2"}',
+        '{{}}',
+      ]);
+    });
+
+    test('for trailing commas', () => {
+      expectActionIssue(action, baseIssue, [
+        '{"key":"value"},',
+        '{"key":"value",}',
+        '[1, 2, 3,]',
+      ]);
+    });
+  });
+});
diff --git a/library/src/actions/json/json.ts b/library/src/actions/json/json.ts
new file mode 100644
index 00000000..ff877a4d
--- /dev/null
+++ b/library/src/actions/json/json.ts
@@ -0,0 +1,107 @@
+import type {
+  BaseIssue,
+  BaseValidation,
+  ErrorMessage,
+} from '../../types/index.ts';
+import { _addIssue } from '../../utils/index.ts';
+
+/**
+ * JSON issue type.
+ */
+export interface JsonIssue<TInput extends string> extends BaseIssue<TInput> {
+  /**
+   * The issue kind.
+   */
+  readonly kind: 'validation';
+  /**
+   * The issue type.
+   */
+  readonly type: 'json';
+  /**
+   * The expected property.
+   */
+  readonly expected: null;
+  /**
+   * The received property.
+   */
+  readonly received: `"${string}"`;
+  /**
+   * The JSON validation requirement.
+   */
+  readonly requirement: (input: string) => boolean;
+}
+
+/**
+ * JSON action type.
+ */
+export interface JsonAction<
+  TInput extends string,
+  TMessage extends ErrorMessage<JsonIssue<TInput>> | undefined,
+> extends BaseValidation<TInput, TInput, JsonIssue<TInput>> {
+  /**
+   * The action type.
+   */
+  readonly type: 'json';
+  /**
+   * The action reference.
+   */
+  readonly reference: typeof json;
+  /**
+   * The expected property.
+   */
+  readonly expects: null;
+  /**
+   * The JSON validation requirement.
+   */
+  readonly requirement: (input: string) => boolean;
+  /**
+   * The error message.
+   */
+  readonly message: TMessage;
+}
+
+/**
+ * Creates a [JSON](https://en.wikipedia.org/wiki/JSON) validation action.
+ *
+ * @returns A JSON action.
+ */
+export function json<TInput extends string>(): JsonAction<TInput, undefined>;
+
+/**
+ * Creates a [JSON](https://en.wikipedia.org/wiki/JSON) validation action.
+ *
+ * @param message The error message.
+ *
+ * @returns A JSON action.
+ */
+export function json<
+  TInput extends string,
+  const TMessage extends ErrorMessage<JsonIssue<TInput>> | undefined,
+>(message: TMessage): JsonAction<TInput, TMessage>;
+
+export function json(
+  message?: ErrorMessage<JsonIssue<string>>
+): JsonAction<string, ErrorMessage<JsonIssue<string>> | undefined> {
+  return {
+    kind: 'validation',
+    type: 'json',
+    reference: json,
+    async: false,
+    expects: null,
+    requirement(input) {
+      try {
+        JSON.parse(input);
+        return true;
+      } catch {
+        return false;
+      }
+    },
+    message,
+    '~run'(dataset, config) {
+      if (dataset.typed && !this.requirement(dataset.value)) {
+        _addIssue(this, 'JSON', dataset, config);
+      }
+      return dataset;
+    },
+  };
+}