diff --git a/deprecations.d.ts b/deprecations.d.ts
new file mode 100644
index 0000000..0fb0f2a
--- /dev/null
+++ b/deprecations.d.ts
@@ -0,0 +1,10 @@
+type NonZeroDigit = '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
+type Digit = '0' | NonZeroDigit;
+type Digits = `${NonZeroDigit}${Digit | string}`;
+
+type Triple = `${Digits}.${Digits}.${Digits}`;
+type PreRelease = `-${string}`;
+
+export type Semver = `${Triple}${PreRelease | ''}`;
+
+export type DeprecationsByVersion = { [version: Semver]: string };
diff --git a/index.js b/index.js
index c50acb5..0798a1e 100644
--- a/index.js
+++ b/index.js
@@ -5,28 +5,43 @@ const fromEntries = require('object.fromentries');
 const entries = require('object.entries');
 const pacote = require('pacote');
 
-const isString = (str) => typeof str === 'string';
+const isString = /** @type {(str: unknown) => str is string} */ (str) => typeof str === 'string';
 
 const { from } = Array;
 
+/** @typedef {import('./deprecations').DeprecationsByVersion} DeprecationsByVersion */
+
+/** @type {<T extends string = string>(...packageNames: T[]) => Promise<Record<T, DeprecationsByVersion>>} */
 module.exports = function deprecations(packageName, ...morePackageNames) {
 	if (arguments.length < 1) {
 		throw new TypeError('at least 1 package name is required');
 	}
 
+	// @ts-expect-error https://github.com/microsoft/TypeScript/issues/57164
 	if (!every(arguments, isString)) {
 		throw new TypeError('module names must all be strings');
 	}
 
-	return Promise.all(from(arguments, async (name) => {
-		const { versions } = await pacote.packument(name, { fullMetadata: true });
-		return [
-			name,
-			fromEntries(entries(versions).map(([version, { deprecated }]) => [
-				version,
-				deprecated,
-			])),
-		];
-	})).then(fromEntries);
+	const depEntries = Promise.all(from(
+		arguments,
+		/** @type {(name: string) => Promise<[name, DeprecationsByVersion]>} */ async (name) => {
+			const { versions } = await pacote.packument(name, { fullMetadata: true });
+			// eslint-disable-next-line no-extra-parens
+			const obj = /** @type {DeprecationsByVersion} */ (
+				fromEntries(entries(versions).map(([
+					version,
+					{ deprecated },
+				]) => [
+					version,
+					deprecated,
+				]))
+			);
+			return [
+				name,
+				obj,
+			];
+		},
+	));
+	return depEntries.then(fromEntries);
 };
 
diff --git a/package.json b/package.json
index 7b82d3f..72749a3 100644
--- a/package.json
+++ b/package.json
@@ -46,13 +46,19 @@
 	},
 	"devDependencies": {
 		"@ljharb/eslint-config": "^21.1.0",
+		"@types/array.prototype.every": "^1.1.0",
+		"@types/object.entries": "^1.1.0",
+		"@types/object.fromentries": "^2.0.4",
+		"@types/pacote": "^11.1.8",
+		"@types/tape": "^5.6.4",
 		"aud": "^2.0.4",
 		"eslint": "=8.8.0",
 		"in-publish": "^2.0.1",
 		"npmignore": "^0.3.1",
 		"nyc": "^15.1.0",
 		"safe-publish-latest": "^2.0.0",
-		"tape": "^5.7.4"
+		"tape": "^5.7.4",
+		"typescript": "^5.4.0-dev.20240127"
 	},
 	"engines": {
 		"node": "^18.17.0 || >=20.5.0"
diff --git a/test/index.js b/test/index.js
index 297205d..8352bd8 100644
--- a/test/index.js
+++ b/test/index.js
@@ -2,20 +2,20 @@
 
 const deprecations = require('../');
 const test = require('tape');
+const fromEntries = require('object.fromentries');
 
+/** @type {<T extends object>(obj: T) => Partial<T>} */
 const compact = function (obj) {
-	return Object.keys(obj).reduce((map, key) => {
-		if (obj[key]) {
-			map[key] = obj[key]; // eslint-disable-line no-param-reassign
-		}
-		return map;
-	}, {});
+	return fromEntries(Object.entries(obj).filter(([, value]) => value));
 };
 
 test('errors', (t) => {
 	t.throws(deprecations, new TypeError('at least 1 package name is required'));
+	// @ts-expect-error
 	t.throws(() => { deprecations(3); }, new TypeError('module names must all be strings'));
+	// @ts-expect-error
 	t.throws(() => { deprecations('foo', 3); }, new TypeError('module names must all be strings'));
+	// @ts-expect-error
 	t.throws(() => { deprecations(3, 'foo'); }, new TypeError('module names must all be strings'));
 	t.end();
 });
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..210a000
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,49 @@
+{
+	"compilerOptions": {
+		/* Visit https://aka.ms/tsconfig.json to read more about this file */
+
+		/* Projects */
+
+		/* Language and Environment */
+		"target": "es2022",																	/* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
+		// "lib": [],																				/* Specify a set of bundled library declaration files that describe the target runtime environment. */
+		// "noLib": true,																		/* Disable including any library files, including the default lib.d.ts. */
+		"useDefineForClassFields": true,										 /* Emit ECMAScript-standard-compliant class fields. */
+		// "moduleDetection": "auto",												/* Control what method is used to detect module-format JS files. */
+
+		/* Modules */
+		"module": "commonjs",																/* Specify what module code is generated. */
+		// "rootDir": "./",																	/* Specify the root folder within your source files. */
+		// "moduleResolution": "node",											 /* Specify how TypeScript looks up a file from a given module specifier. */
+		// "baseUrl": "./",																	/* Specify the base directory to resolve non-relative module names. */
+		// "paths": {},																			/* Specify a set of entries that re-map imports to additional lookup locations. */
+		// "rootDirs": [],																	 /* Allow multiple folders to be treated as one when resolving modules. */
+		// "typeRoots": ["types"],													 /* Specify multiple folders that act like `./node_modules/@types`. */
+		"resolveJsonModule": true,													 /* Enable importing .json files. */
+		// "allowArbitraryExtensions": true,								 /* Enable importing files with any extension, provided a declaration file is present. */
+
+		/* JavaScript Support */
+		"allowJs": true,																		 /* Allow JavaScript files to be a part of your program. Use the `checkJS` option to get errors from these files. */
+		"checkJs": true,																		 /* Enable error reporting in type-checked JavaScript files. */
+		"maxNodeModuleJsDepth": 1,													 /* Specify the maximum folder depth used for checking JavaScript files from `node_modules`. Only applicable with `allowJs`. */
+
+		/* Emit */
+		"declaration": true,																 /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
+		"declarationMap": true,															/* Create sourcemaps for d.ts files. */
+		"noEmit": true,																			/* Disable emitting files from a compilation. */
+
+		/* Interop Constraints */
+		"allowSyntheticDefaultImports": true,								/* Allow `import x from y` when a module doesn't have a default export. */
+		"esModuleInterop": true,														 /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables `allowSyntheticDefaultImports` for type compatibility. */
+		"forceConsistentCasingInFileNames": true,						/* Ensure that casing is correct in imports. */
+
+		/* Type Checking */
+		"strict": true,																			/* Enable all strict type-checking options. */
+
+		/* Completeness */
+		// "skipLibCheck": true															/* Skip type checking all .d.ts files. */
+	},
+	"exclude": [
+		"coverage",
+	],
+}