diff --git a/code-contract.test.ts b/code-contract.test.ts
new file mode 100644
index 0000000..a2d6b45
--- /dev/null
+++ b/code-contract.test.ts
@@ -0,0 +1,122 @@
+/**
+ * @file Unit tests for code contract utility
+ */
+import {
+  assertEquals,
+  assertThrows,
+} from "https://deno.land/std/testing/asserts.ts";
+
+import {
+  codeContract,
+  disableContract,
+  enableContract,
+} from "./code-contract.ts";
+
+//
+// Variables
+//
+
+let sideEffectTarget = true;
+
+//
+// Functions
+//
+
+const func = (lhs: number, rhs: number) => (lhs + rhs);
+
+//
+// Test cases
+//
+
+Deno.test({
+  name: "It should success the function call if the contract is kept",
+  fn: () => {
+    // arrange
+    enableContract();
+    sideEffectTarget = false;
+    const contracted = codeContract(func, {
+      pre: (lhs: number, rhs: number) => 0 < lhs && 0 < rhs,
+      post: (result: number) => (result === 30),
+    });
+
+    // act & assert
+    assertEquals(contracted(10, 20), 30);
+  },
+});
+Deno.test({
+  name: "It should fail the function call if the pre condition is invalid",
+  fn: () => {
+    assertThrows(
+      () => {
+        // arrange
+        enableContract();
+        sideEffectTarget = false;
+        const contracted = codeContract(func, {
+          pre: (lhs: number, rhs: number) => 0 < lhs && 0 < rhs,
+        });
+
+        // act & assert
+        assertEquals(contracted(20, -10), 10);
+      },
+    );
+  },
+});
+Deno.test({
+  name: "It should fail the function call if the post condition is invalid",
+  fn: () => {
+    assertThrows(
+      () => {
+        // arrange
+        enableContract();
+        sideEffectTarget = false;
+        const contracted = codeContract(func, {
+          post: (result: number) => (result === 30),
+        });
+
+        // act & assert
+        assertEquals(contracted(20, 20), 40);
+      },
+    );
+  },
+});
+Deno.test({
+  name:
+    "It should fail the function call if the invariant condition is invalid",
+  fn: () => {
+    assertThrows(
+      () => {
+        // arrange
+        enableContract();
+        sideEffectTarget = false;
+
+        const funcWithSideEffect = (
+          lhs: number,
+          rhs: number,
+        ) => (sideEffectTarget = true, lhs + rhs);
+        const contracted = codeContract(funcWithSideEffect, {
+          invariant: () => (sideEffectTarget === false),
+        });
+
+        // act & assert
+        assertEquals(contracted(20, 20), 40);
+      },
+    );
+  },
+});
+Deno.test({
+  name: "It should omit contract check if contract check is disabled",
+  fn: () => {
+    // arrange
+    disableContract();
+    sideEffectTarget = false;
+    const contracted = codeContract(func, {
+      pre: (lhs: number, rhs: number) => 0 < lhs && 0 < rhs,
+      post: (result: number) => (result === 30),
+    });
+
+    // act & assert
+    assertEquals(contracted(-10, -20), -30);
+
+    enableContract();
+  },
+});
diff --git a/code-contract.ts b/code-contract.ts
new file mode 100644
index 0000000..647665c
--- /dev/null
+++ b/code-contract.ts
@@ -0,0 +1,102 @@
+/**
+ * @file Code contract utility
+ */
+//
+// Types
+//
+
+// deno-lint-ignore no-explicit-any
+type FunctionType<T> = ((...args: any[]) => T) & { name: string };
+type ContractType<TResult> = {
+  // deno-lint-ignore no-explicit-any
+  pre?: (...args: any[]) => boolean;
+  post?: (result: TResult) => boolean;
+  invariant?: () => boolean;
+};
+
+//
+// Variables
+//
+
+let checkContract = true;
+
+//
+// Functions
+//
+
+/**
+ * Bind function with code contract
+ * @param fn Function to bind
+ * @param contract Code contract
+ * @returns Bound function
+ */
+export function codeContract<
+  T extends FunctionType<ReturnType<T>>,
+>(
+  fn: T,
+  contract: ContractType<ReturnType<T>> = {},
+): T {
+  if (checkContract === false) {
+    return fn;
+  }
+  return ((...args) => {
+    const check = requireContractCheck();
+    if (
+      check !== false && contract.pre !== undefined &&
+      contract.pre(...args) === false
+    ) {
+      const msg = [
+        "Code Contract: Failed to assert the pre condition.",
+        `\tfunction: ${fn.name}`,
+        `\targs: ${JSON.stringify(args)}`,
+      ];
+      throw new Error(msg.join("\n"));
+    }
+    const result = fn(...args);
+    if (
+      check !== false && contract.post !== undefined &&
+      contract.post(result) === false
+    ) {
+      const msg = [
+        "Code Contract: Failed to assert the post condition.",
+        `\tfunction: ${fn.name}`,
+        `\tresult: ${JSON.stringify(args)}`,
+      ];
+      throw new Error(msg.join("\n"));
+    }
+    if (
+      check !== false && contract.invariant !== undefined &&
+      contract.invariant() === false
+    ) {
+      const msg = [
+        "Code Contract: Failed to assert the invariant.",
+        `\tfunction: ${fn.name}`,
+      ];
+      throw new Error(msg.join("\n"));
+    }
+
+    return result;
+  }) as T;
+}
+
+/**
+ * Enable contract
+ */
+export function enableContract() {
+  checkContract = true;
+}
+
+/**
+ * Disable contract check
+ */
+export function disableContract() {
+  checkContract = false;
+}
+
+/**
+ * Require contract check
+ * @returns Require contract check flag
+ */
+function requireContractCheck() {
+  return checkContract;
+}
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..0f11fb7
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "strict": true
+  }
+}