diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..9217ef6
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,16 @@
+export type EnvSchemaData = {
+  [key: string]: unknown;
+};
+
+export type EnvSchemaOpt = {
+  schema?: object;
+  data?: [EnvSchemaData, ...EnvSchemaData[]] | EnvSchemaData;
+  env?: boolean;
+  dotenv?: boolean | object;
+};
+
+declare function loadAndValidateEnvironment(
+  _opts?: EnvSchemaOpt
+): EnvSchemaData;
+
+export default loadAndValidateEnvironment;
diff --git a/package.json b/package.json
index 2f0711b..c24ac49 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,8 @@
   "description": "Validate your env variable using Ajv and dotenv",
   "main": "index.js",
   "scripts": {
-    "test": "standard | snazzy && tap test/*.test.js"
+    "test": "standard | snazzy && tap test/*.test.js && npm run typescript",
+    "typescript": "tsd"
   },
   "repository": {
     "type": "git",
@@ -30,7 +31,8 @@
     "pre-commit": "^1.2.2",
     "snazzy": "^8.0.0",
     "standard": "^14.0.2",
-    "tap": "^12.7.0"
+    "tap": "^12.7.0",
+    "tsd": "^0.13.1"
   },
   "dependencies": {
     "ajv": "^6.10.2",
@@ -41,5 +43,8 @@
       "dotenv",
       "tap"
     ]
+  },
+  "tsd": {
+    "directory": "test/types"
   }
 }
diff --git a/test/types/types.test.ts b/test/types/types.test.ts
new file mode 100644
index 0000000..9176aca
--- /dev/null
+++ b/test/types/types.test.ts
@@ -0,0 +1,55 @@
+import { expectError, expectType } from "tsd";
+import envSchema, { EnvSchemaData, EnvSchemaOpt } from "../..";
+
+const schema = {
+  type: "object",
+  required: ["PORT"],
+  properties: {
+    PORT: {
+      type: "string",
+      default: 3000,
+    },
+  },
+};
+const data = {
+  foo: "bar",
+};
+
+expectType<EnvSchemaData>(envSchema());
+
+const emptyOpt: EnvSchemaOpt = {};
+expectType<EnvSchemaOpt>(emptyOpt);
+
+const optWithSchema: EnvSchemaOpt = {
+  schema,
+};
+expectType<EnvSchemaOpt>(optWithSchema);
+
+const optWithData: EnvSchemaOpt = {
+  data,
+};
+expectType<EnvSchemaOpt>(optWithData);
+
+expectError<EnvSchemaOpt>({
+  data: [], // min 1 item
+});
+
+const optWithArrayData: EnvSchemaOpt = {
+  data: [{}],
+};
+expectType<EnvSchemaOpt>(optWithArrayData);
+
+const optWithMultipleItemArrayData: EnvSchemaOpt = {
+  data: [{}, {}],
+};
+expectType<EnvSchemaOpt>(optWithMultipleItemArrayData);
+
+const optWithDotEnvBoolean: EnvSchemaOpt = {
+  dotenv: true,
+};
+expectType<EnvSchemaOpt>(optWithDotEnvBoolean);
+
+const optWithDotEnvOpt: EnvSchemaOpt = {
+  dotenv: true,
+};
+expectType<EnvSchemaOpt>(optWithDotEnvOpt);