diff --git a/.npmrc b/.npmrc
new file mode 100644
index 0000000..9cf9495
--- /dev/null
+++ b/.npmrc
@@ -0,0 +1 @@
+package-lock=false
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
index df60d14..9198515 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,5 +4,13 @@ node_js:
   - 10
   - 12
   - 14
+script: >
+  node_version="$(node -v)";
+  if  [ "${node_version:1:1}" -eq 8 ]; then
+      # tsd test runner doesn't work on node 8
+      npm run test:no-types;
+  else
+      npm test;
+  fi
 after_script:
   - coveralls < coverage/lcov.info
diff --git a/index.d.ts b/index.d.ts
index 23e46ca..20fc937 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,4 +1,66 @@
-declare module 'fast-json-stable-stringify' {
-  function stringify(obj: any): string;
-  export = stringify;
+export = stringify;
+
+/**
+ * Deterministic `JSON.stringify()`.
+ * 
+ * @returns A deterministic stringified string from the object `obj`.
+ * 
+ * @example
+ * import stringify = require('fast-json-stable-stringify');
+ * 
+ * const obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
+ * console.log(stringify(obj));
+ * // -> {"a":3,"b":[{"x":4,"y":5,"z":6},7],"c":8}
+ */
+declare function stringify(
+  obj: any,
+  options?: stringify.Options | stringify.Comparator
+): string;
+
+declare namespace stringify {
+  interface Options {
+    /**
+     * You can supply a custom comparison function for object keys.
+     * 
+     * @example
+     * // For example, to sort on the object key names in reverse order you could write:
+     * 
+     * import stringify = require('fast-json-stable-stringify');
+     * 
+     * const obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
+     * const s = stringify(obj, (a, b) => {
+     *     return a.key < b.key ? 1 : -1;
+     * });
+     * console.log(s);
+     * // -> {"c":8,"b":[{"z":6,"y":5,"x":4},7],"a":3}
+     * 
+     * @example
+     * // Or if you wanted to sort on the object values in reverse order, you could write:
+     * 
+     * import stringify = require('fast-json-stable-stringify');
+     * 
+     * const obj = { d: 6, c: 5, b: [{z:3,y:2,x:1},9], a: 10 };
+     * const s = stringify(obj, (a, b) => {
+     *     return a.value < b.value ? 1 : -1;
+     * });
+     * console.log(s);
+     * // -> {"d":6,"c":5,"b":[{"z":3,"y":2,"x":1},9],"a":10}
+     */
+    cmp?: Comparator;
+
+    /**
+     * Pass `true` to stringify circular property as `__cycle__` - the result will not be
+     * a valid JSON string in this case.
+     * 
+     * TypeError will be thrown in case of circular object without this option.
+     */
+    cycles?: boolean;
+  }
+
+  type Comparator = (a: CompareDescriptor, b: CompareDescriptor) => number;
+
+  interface CompareDescriptor {
+    key: string;
+    value: any;
+  }
 }
diff --git a/package.json b/package.json
index 754d4d2..a523d83 100644
--- a/package.json
+++ b/package.json
@@ -14,12 +14,15 @@
     "json-stable-stringify": "latest",
     "nyc": "^14.1.0",
     "pre-commit": "^1.2.2",
-    "tape": "^4.11.0"
+    "tape": "^4.11.0",
+    "tsd": "^0.16.0"
   },
   "scripts": {
     "eslint": "eslint index.js test",
     "test-spec": "tape test/*.js",
-    "test": "npm run eslint && nyc npm run test-spec"
+    "test-types": "tsd",
+    "test": "npm run eslint && nyc npm run test-spec && npm run test-types",
+    "test:no-types": "npm run eslint && nyc npm run test-spec"
   },
   "repository": {
     "type": "git",
@@ -49,6 +52,9 @@
       "text-summary"
     ]
   },
+  "tsd": {
+    "directory": "test"
+  },
   "engines": {
     "node": ">=8"
   }
diff --git a/test/index.test-d.ts b/test/index.test-d.ts
new file mode 100644
index 0000000..4184900
--- /dev/null
+++ b/test/index.test-d.ts
@@ -0,0 +1,28 @@
+import { expectType } from "tsd";
+import stringify = require("../index");
+
+// test type exports
+type CompareDescriptor = stringify.CompareDescriptor;
+type Comparator = stringify.Comparator;
+type Options = stringify.Options;
+
+const obj = { c: 8, b: [{ z: 6, y: 5, x: 4 }, 7], a: 3 };
+
+expectType<string>(stringify(obj));
+expectType<string>(
+  stringify(obj, (a, b) => {
+    expectType<CompareDescriptor>(a);
+    expectType<CompareDescriptor>(b);
+    return a.key < b.key ? 1 : -1;
+  })
+);
+expectType<string>(
+  stringify(obj, {
+    cmp(a, b) {
+      expectType<CompareDescriptor>(a);
+      expectType<CompareDescriptor>(b);
+      return a.key < b.key ? 1 : -1;
+    },
+  })
+);
+expectType<string>(stringify(obj, { cycles: true }));