diff --git a/.gitignore b/.gitignore
index c5726c0..b309e7f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@ node_modules
 npm-debug.log
 .DS_Store
 package-lock.json
+yarn.lock
 /.idea
 .eslintcache
 /lcov.info
diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..fe3ea8c
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,14 @@
+import { Transform } from 'node:stream'
+
+type ConfigurationPojo = {
+  pattern: string
+  outFile?: string
+  prependSourceFiles?: boolean
+  prependPathFix?: string
+  legacyTempFile?: boolean
+  ignore?: string[]
+}
+
+export function mergeCoverageReportFiles(filePaths: string[], options: ConfigurationPojo): Promise<string>
+
+export function mergeCoverageReportFilesStream(filePathsOrMergeOptions: string[] | ConfigurationPojo, mergeOptions?: ConfigurationPojo): Transform
diff --git a/package.json b/package.json
index 3c7a460..a3f12db 100644
--- a/package.json
+++ b/package.json
@@ -2,15 +2,18 @@
   "name": "lcov-result-merger",
   "description": "Merges multiple lcov results into one",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
     "index.js",
+    "index.d.ts",
     "bin",
     "lib"
   ],
   "scripts": {
     "lint": "eslint . --cache",
-    "test": "npm run lint && npm run test:js",
+    "test": "npm run lint && npm run test:js && npm run test:dts",
     "test:js": "mocha --bail --recursive",
+    "test:dts": "tsd -f test/test-types/index.test-d.ts",
     "test:coverage": "nyc --reporter=html --reporter=lcov mocha -- --recursive",
     "release": "release-it",
     "cleanup": "rm -rf ./.nyc_output ./coverage ./.eslintcache"
@@ -45,6 +48,7 @@
   },
   "devDependencies": {
     "@release-it/conventional-changelog": "^6.0.0",
+    "@types/node": "^20.9.0",
     "@types/yargs": "^17.0.10",
     "chai": "^4.1.2",
     "eslint": "^8.30.0",
@@ -57,7 +61,8 @@
     "nyc": "^15.1.0",
     "prettier": "2.8.1",
     "release-it": "^15.11.0",
-    "rimraf": "^5.0.1"
+    "rimraf": "^5.0.1",
+    "tsd": "^0.29.0"
   },
   "engines": {
     "node": ">=14"
diff --git a/test/test-types/index.test-d.ts b/test/test-types/index.test-d.ts
new file mode 100644
index 0000000..03b7240
--- /dev/null
+++ b/test/test-types/index.test-d.ts
@@ -0,0 +1,10 @@
+import { expectType, expectError } from 'tsd'
+import { Transform } from 'node:stream'
+import { mergeCoverageReportFilesStream, mergeCoverageReportFiles } from '../../index'
+
+expectType<Promise<string>>(mergeCoverageReportFiles(['a', 'b'], {pattern: 'a'}))
+expectType<Transform>(mergeCoverageReportFilesStream(['a', 'b'], {pattern: 'a'}))
+expectType<Transform>(mergeCoverageReportFilesStream({pattern: 'a'}))
+
+expectError(mergeCoverageReportFiles(['a', 'b'], {pattern: 1}))
+expectError(mergeCoverageReportFiles(['a', 'b']))