diff --git a/package.json b/package.json
index 34559f8..1bb3e97 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,8 @@
 		"node": ">=18.19"
 	},
 	"scripts": {
-		"test": "xo && c8 ava && tsc ./source/index.d.ts"
+		"test": "xo && c8 ava && npm run type",
+		"type": "tsd -t ./source/index.d.ts -f ./source/index.test-d.ts"
 	},
 	"files": [
 		"source/**/*.js",
@@ -47,11 +48,13 @@
 		"execa"
 	],
 	"devDependencies": {
+		"@types/node": "^22.5.4",
 		"ava": "^6.1.3",
 		"c8": "^10.1.2",
 		"get-node": "^15.0.1",
 		"path-key": "^4.0.0",
 		"tempy": "^3.1.0",
+		"tsd": "^0.31.2",
 		"typescript": "^5.5.4",
 		"xo": "^0.59.3",
 		"yoctocolors": "^2.1.1"
diff --git a/source/index.d.ts b/source/index.d.ts
index f04a577..7a1f382 100644
--- a/source/index.d.ts
+++ b/source/index.d.ts
@@ -1,12 +1,52 @@
-export type Options = {
-	readonly timeout: number;
-	readonly signal: AbortSignal;
-	// Readonly nativeOptions;
+import type {ChildProcess, SpawnOptions} from 'node:child_process';
+
+type StdioOption = Readonly<Exclude<SpawnOptions['stdio'], undefined>[number]>;
+type StdinOption = StdioOption | {readonly string?: string};
+
+export type Options = Omit<SpawnOptions, 'env' | 'stdio'> & Readonly<Partial<{
+	stdin: StdinOption;
+
+	stdout: StdioOption;
+
+	stderr: StdioOption;
+
+	stdio: SpawnOptions['stdio'] | readonly [StdinOption, ...readonly StdioOption[]];
+
+	preferLocal: boolean;
+
+	// Fixes issues with Remix and Next.js
+	// See https://github.com/sindresorhus/execa/pull/1141
+	env: Readonly<Partial<Record<string, string>>>;
+}>>;
+
+export type Result = {
+	stdout: string;
+
+	stderr: string;
+
+	output: string;
+
+	command: string;
+
+	durationMs: number;
+};
+
+export type SubprocessError = Error & Result & {
+	exitCode?: number;
+
+	signalName?: string;
+};
+
+export type Subprocess = Promise<Result> & AsyncIterable<string> & {
+	nodeChildProcess: Promise<ChildProcess>;
+
+	stdout: AsyncIterable<string>;
+
+	stderr: AsyncIterable<string>;
+
+	pipe(file: string, arguments?: readonly string[], options?: Options): Subprocess;
+	pipe(file: string, options?: Options): Subprocess;
 };
 
-// TODO: Finish this when the API is decided on.
-export function nanoSpawn(
-	command: string,
-	arguments: readonly string[],
-	options?: Options
-): Promise<void>;
+export default function nanoSpawn(file: string, arguments?: readonly string[], options?: Options): Subprocess;
+export default function nanoSpawn(file: string, options?: Options): Subprocess;
diff --git a/source/index.test-d.ts b/source/index.test-d.ts
new file mode 100644
index 0000000..b142536
--- /dev/null
+++ b/source/index.test-d.ts
@@ -0,0 +1,144 @@
+import type {ChildProcess} from 'node:child_process';
+import {
+	expectType,
+	expectAssignable,
+	expectNotAssignable,
+	expectError,
+} from 'tsd';
+import nanoSpawn, {
+	type Options,
+	type Result,
+	type SubprocessError,
+	type Subprocess,
+} from './index.js';
+
+try {
+	const result = await nanoSpawn('test');
+	expectType<Result>(result);
+	expectType<string>(result.stdout);
+	expectType<string>(result.stderr);
+	expectType<string>(result.output);
+	expectType<string>(result.command);
+	expectType<number>(result.durationMs);
+	expectNotAssignable<Error>(result);
+	expectError(result.exitCode);
+	expectError(result.signalName);
+	expectError(result.other);
+} catch (error) {
+	const subprocessError = error as SubprocessError;
+	expectType<string>(subprocessError.stdout);
+	expectType<string>(subprocessError.stderr);
+	expectType<string>(subprocessError.output);
+	expectType<string>(subprocessError.command);
+	expectType<number>(subprocessError.durationMs);
+	expectAssignable<Error>(subprocessError);
+	expectType<number | undefined>(subprocessError.exitCode);
+	expectType<string | undefined>(subprocessError.signalName);
+	expectError(subprocessError.other);
+}
+
+expectAssignable<Options>({} as const);
+expectAssignable<Options>({argv0: 'test'} as const);
+expectNotAssignable<Options>({other: 'test'} as const);
+expectNotAssignable<Options>('test');
+
+await nanoSpawn('test', {argv0: 'test'} as const);
+expectError(await nanoSpawn('test', {argv0: true} as const));
+await nanoSpawn('test', {preferLocal: true} as const);
+expectError(await nanoSpawn('test', {preferLocal: 'true'} as const));
+await nanoSpawn('test', {env: {}} as const);
+// eslint-disable-next-line @typescript-eslint/naming-convention
+await nanoSpawn('test', {env: {TEST: 'test'}} as const);
+expectError(await nanoSpawn('test', {env: true} as const));
+// eslint-disable-next-line @typescript-eslint/naming-convention
+expectError(await nanoSpawn('test', {env: {TEST: true}} as const));
+await nanoSpawn('test', {stdin: 'pipe'} as const);
+await nanoSpawn('test', {stdin: {string: 'test'} as const} as const);
+expectError(await nanoSpawn('test', {stdin: {string: true} as const} as const));
+expectError(await nanoSpawn('test', {stdin: {other: 'test'} as const} as const));
+expectError(await nanoSpawn('test', {stdin: true} as const));
+await nanoSpawn('test', {stdout: 'pipe'} as const);
+expectError(await nanoSpawn('test', {stdout: {string: 'test'} as const} as const));
+expectError(await nanoSpawn('test', {stdout: true} as const));
+await nanoSpawn('test', {stderr: 'pipe'} as const);
+expectError(await nanoSpawn('test', {stderr: {string: 'test'} as const} as const));
+expectError(await nanoSpawn('test', {stderr: true} as const));
+await nanoSpawn('test', {stdio: ['pipe', 'pipe', 'pipe'] as const} as const);
+await nanoSpawn('test', {stdio: [{string: 'test'} as const, 'pipe', 'pipe'] as const} as const);
+expectError(await nanoSpawn('test', {stdio: ['pipe', {string: 'test'} as const, 'pipe'] as const} as const));
+expectError(await nanoSpawn('test', {stdio: ['pipe', 'pipe', {string: 'test'} as const] as const} as const));
+expectError(await nanoSpawn('test', {stdio: [{string: true} as const, 'pipe', 'pipe'] as const} as const));
+expectError(await nanoSpawn('test', {stdio: [{other: 'test'} as const, 'pipe', 'pipe'] as const} as const));
+expectError(await nanoSpawn('test', {stdio: [true, true, true] as const} as const));
+await nanoSpawn('test', {stdio: 'pipe'} as const);
+expectError(await nanoSpawn('test', {stdio: true} as const));
+expectError(await nanoSpawn('test', {other: 'test'} as const));
+
+expectError(await nanoSpawn());
+expectError(await nanoSpawn(true));
+await nanoSpawn('test', [] as const);
+await nanoSpawn('test', ['one'] as const);
+expectError(await nanoSpawn('test', [true] as const));
+await nanoSpawn('test', {} as const);
+expectError(await nanoSpawn('test', true));
+await nanoSpawn('test', ['one'] as const, {} as const);
+expectError(await nanoSpawn('test', ['one'] as const, true));
+expectError(await nanoSpawn('test', ['one'] as const, {} as const, true));
+
+expectError(await nanoSpawn('test').pipe());
+expectError(await nanoSpawn('test').pipe(true));
+await nanoSpawn('test').pipe('test', [] as const);
+await nanoSpawn('test').pipe('test', ['one'] as const);
+expectError(await nanoSpawn('test').pipe('test', [true] as const));
+await nanoSpawn('test').pipe('test', {} as const);
+expectError(await nanoSpawn('test').pipe('test', true));
+await nanoSpawn('test').pipe('test', ['one'] as const, {} as const);
+expectError(await nanoSpawn('test').pipe('test', ['one'] as const, true));
+expectError(await nanoSpawn('test').pipe('test', ['one'] as const, {} as const, true));
+
+expectError(await nanoSpawn('test').pipe('test').pipe());
+expectError(await nanoSpawn('test').pipe('test').pipe(true));
+await nanoSpawn('test').pipe('test').pipe('test', [] as const);
+await nanoSpawn('test').pipe('test').pipe('test', ['one'] as const);
+expectError(await nanoSpawn('test').pipe('test').pipe('test', [true] as const));
+await nanoSpawn('test').pipe('test').pipe('test', {} as const);
+expectError(await nanoSpawn('test').pipe('test').pipe('test', true));
+await nanoSpawn('test').pipe('test').pipe('test', ['one'] as const, {} as const);
+expectError(await nanoSpawn('test').pipe('test').pipe('test', ['one'] as const, true));
+expectError(await nanoSpawn('test').pipe('test').pipe('test', ['one'] as const, {} as const, true));
+
+expectType<Subprocess>(nanoSpawn('test').pipe('test'));
+expectType<Subprocess>(nanoSpawn('test').pipe('test').pipe('test'));
+expectType<Result>(await nanoSpawn('test').pipe('test'));
+expectType<Result>(await nanoSpawn('test').pipe('test').pipe('test'));
+
+for await (const line of nanoSpawn('test')) {
+	expectType<string>(line);
+}
+
+for await (const line of nanoSpawn('test').pipe('test')) {
+	expectType<string>(line);
+}
+
+for await (const line of nanoSpawn('test').stdout) {
+	expectType<string>(line);
+}
+
+for await (const line of nanoSpawn('test').pipe('test').stdout) {
+	expectType<string>(line);
+}
+
+for await (const line of nanoSpawn('test').stderr) {
+	expectType<string>(line);
+}
+
+for await (const line of nanoSpawn('test').pipe('test').stderr) {
+	expectType<string>(line);
+}
+
+const subprocess = nanoSpawn('test');
+expectType<Subprocess>(subprocess);
+
+const nodeChildProcess = await subprocess.nodeChildProcess;
+expectType<ChildProcess>(nodeChildProcess);
+expectType<number | undefined>(nodeChildProcess.pid);
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..09fcfd6
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,11 @@
+{
+	"compilerOptions": {
+		"module": "nodenext",
+		"moduleResolution": "nodenext",
+		"target": "ES2022",
+		"strict": true
+	},
+	"files": [
+		"source/index.d.ts"
+	]
+}