diff --git a/.eslintrc.json b/.eslintrc.json
index 27db61f841..4c45bf5290 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -15,6 +15,7 @@
   ],
   "globals": { "BigInt": true, "console": true, "WebAssembly": true },
   "rules": {
+    "@typescript-eslint/explicit-function-return-type": ["error"],
     "@typescript-eslint/explicit-module-boundary-types": "off",
     "eslint-comments/disable-enable-pair": [
       "error",
diff --git a/src/chat/index.ts b/src/chat/index.ts
index 70b5925b12..f3a46627ab 100644
--- a/src/chat/index.ts
+++ b/src/chat/index.ts
@@ -13,7 +13,7 @@ import { ChatMessage } from './chat_message';
 
 const ChatContentTopic = 'dingpu';
 
-(async function () {
+(async function (): Promise<void> {
   const opts = processArguments();
 
   const waku = await Waku.create({
@@ -124,7 +124,7 @@ function processArguments(): Options {
   return opts;
 }
 
-function printMessage(chatMsg: ChatMessage) {
+function printMessage(chatMsg: ChatMessage): void {
   const timestamp = chatMsg.timestamp.toLocaleString([], {
     month: 'short',
     day: 'numeric',
diff --git a/src/lib/delay.ts b/src/lib/delay.ts
index 98eaa4f54d..59d8019117 100644
--- a/src/lib/delay.ts
+++ b/src/lib/delay.ts
@@ -1,3 +1,3 @@
-export function delay(ms: number) {
+export function delay(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
diff --git a/src/lib/waku.ts b/src/lib/waku.ts
index 0fba0e37ae..d00e04e337 100644
--- a/src/lib/waku.ts
+++ b/src/lib/waku.ts
@@ -98,16 +98,21 @@ export default class Waku {
    * Dials to the provided peer.
    * @param peer The peer to dial
    */
-  async dial(peer: PeerId | Multiaddr | string) {
-    await this.libp2p.dialProtocol(peer, [RelayCodec, StoreCodec]);
+  async dial(
+    peer: PeerId | Multiaddr | string
+  ): Promise<{
+    stream: import('libp2p-interfaces/src/stream-muxer/types').MuxedStream;
+    protocol: string;
+  }> {
+    return this.libp2p.dialProtocol(peer, [RelayCodec, StoreCodec]);
   }
 
-  addPeerToAddressBook(peerId: PeerId, multiaddr: Multiaddr[]) {
+  addPeerToAddressBook(peerId: PeerId, multiaddr: Multiaddr[]): void {
     this.libp2p.peerStore.addressBook.set(peerId, multiaddr);
   }
 
-  async stop() {
-    await this.libp2p.stop();
+  async stop(): Promise<void> {
+    return this.libp2p.stop();
   }
 
   /**
diff --git a/src/lib/waku_relay/get_relay_peers.ts b/src/lib/waku_relay/get_relay_peers.ts
index 2331da24f5..5f5922ad22 100644
--- a/src/lib/waku_relay/get_relay_peers.ts
+++ b/src/lib/waku_relay/get_relay_peers.ts
@@ -18,7 +18,7 @@ export function getRelayPeers(
   router: Gossipsub,
   topic: string,
   count: number,
-  filter: (id: string) => boolean = () => true
+  filter: (id: string) => boolean = (): boolean => true
 ): Set<string> {
   const peersInTopic = router.topics.get(topic);
   if (!peersInTopic) {
diff --git a/src/lib/waku_relay/index.spec.ts b/src/lib/waku_relay/index.spec.ts
index 427af3c661..2e8eada2e5 100644
--- a/src/lib/waku_relay/index.spec.ts
+++ b/src/lib/waku_relay/index.spec.ts
@@ -32,10 +32,7 @@ describe('Waku Relay', () => {
       }),
     ]);
 
-    await waku1.addPeerToAddressBook(
-      waku2.libp2p.peerId,
-      waku2.libp2p.multiaddrs
-    );
+    waku1.addPeerToAddressBook(waku2.libp2p.peerId, waku2.libp2p.multiaddrs);
 
     await Promise.all([
       new Promise((resolve) =>
@@ -133,7 +130,7 @@ describe('Waku Relay', () => {
 
         await waku.relay.send(message);
 
-        let msgs = [];
+        let msgs: WakuMessage[] = [];
 
         while (msgs.length === 0) {
           await delay(200);
@@ -143,7 +140,7 @@ describe('Waku Relay', () => {
         expect(msgs[0].contentTopic).to.equal(message.contentTopic);
         expect(msgs[0].version).to.equal(message.version);
 
-        const payload = Buffer.from(msgs[0].payload);
+        const payload = Buffer.from(msgs[0].payload!);
         expect(Buffer.compare(payload, message.payload!)).to.equal(0);
       });
 
@@ -216,7 +213,7 @@ describe('Waku Relay', () => {
         await delay(1000);
         await waku.relay.send(message);
 
-        let msgs = [];
+        let msgs: WakuMessage[] = [];
 
         while (msgs.length === 0) {
           console.log('Waiting for messages');
@@ -227,7 +224,7 @@ describe('Waku Relay', () => {
         expect(msgs[0].contentTopic).to.equal(message.contentTopic);
         expect(msgs[0].version).to.equal(message.version);
 
-        const payload = Buffer.from(msgs[0].payload);
+        const payload = Buffer.from(msgs[0].payload!);
         expect(Buffer.compare(payload, message.payload!)).to.equal(0);
       });
 
diff --git a/src/lib/waku_relay/index.ts b/src/lib/waku_relay/index.ts
index 7b92441ace..dccec6eeae 100644
--- a/src/lib/waku_relay/index.ts
+++ b/src/lib/waku_relay/index.ts
@@ -78,7 +78,7 @@ export class WakuRelay extends Gossipsub {
    * @override
    * @returns {void}
    */
-  start() {
+  start(): void {
     super.start();
     super.subscribe(constants.RelayDefaultTopic);
   }
@@ -89,7 +89,7 @@ export class WakuRelay extends Gossipsub {
    * @param {WakuMessage} message
    * @returns {Promise<void>}
    */
-  async send(message: WakuMessage) {
+  async send(message: WakuMessage): Promise<void> {
     const msg = message.encode();
     await super.publish(constants.RelayDefaultTopic, Buffer.from(msg));
   }
diff --git a/src/lib/waku_relay/relay_heartbeat.ts b/src/lib/waku_relay/relay_heartbeat.ts
index 0dc6995e54..21b81cb83f 100644
--- a/src/lib/waku_relay/relay_heartbeat.ts
+++ b/src/lib/waku_relay/relay_heartbeat.ts
@@ -31,10 +31,10 @@ export class RelayHeartbeat extends Heartbeat {
 
     this._heartbeatTimer = {
       _intervalId: undefined,
-      runPeriodically: (fn, period) => {
+      runPeriodically: (fn, period): void => {
         this._heartbeatTimer!._intervalId = setInterval(fn, period);
       },
-      cancel: () => {
+      cancel: (): void => {
         clearTimeout(timeout);
         clearInterval(this._heartbeatTimer?._intervalId as NodeJS.Timeout);
       },
diff --git a/src/test_utils/async_fs.ts b/src/test_utils/async_fs.ts
index ebc63689f9..dc671f45ba 100644
--- a/src/test_utils/async_fs.ts
+++ b/src/test_utils/async_fs.ts
@@ -2,14 +2,14 @@ import fs, { promises as asyncFs } from 'fs';
 import { promisify } from 'util';
 
 import { delay } from '../lib/delay';
-export const existsAsync = (filepath: string) =>
+export const existsAsync = (filepath: string): Promise<void> =>
   asyncFs.access(filepath, fs.constants.F_OK);
 
 export const openAsync = promisify(fs.open);
 
 export const mkdirAsync = asyncFs.mkdir;
 
-export async function waitForFile(path: string) {
+export async function waitForFile(path: string): Promise<void> {
   let found = false;
   do {
     try {
diff --git a/src/test_utils/log_file.ts b/src/test_utils/log_file.ts
index f15f8c4d8d..6412f39c20 100644
--- a/src/test_utils/log_file.ts
+++ b/src/test_utils/log_file.ts
@@ -4,7 +4,10 @@ import { Tail } from 'tail';
 
 import { waitForFile } from './async_fs';
 
-export default async function waitForLine(filepath: string, logLine: string) {
+export default async function waitForLine(
+  filepath: string,
+  logLine: string
+): Promise<void> {
   await pTimeout(waitForFile(filepath), 2000);
 
   const options = {
@@ -22,7 +25,7 @@ export default async function waitForLine(filepath: string, logLine: string) {
   tail.unwatch();
 }
 
-async function find(tail: Tail, line: string) {
+async function find(tail: Tail, line: string): Promise<string> {
   return new Promise((resolve, reject) => {
     tail.on('line', (data: string) => {
       if (data.includes(line)) {
diff --git a/src/test_utils/nim_waku.ts b/src/test_utils/nim_waku.ts
index f8f7efae54..b345087f2c 100644
--- a/src/test_utils/nim_waku.ts
+++ b/src/test_utils/nim_waku.ts
@@ -58,7 +58,7 @@ export class NimWaku {
     this.logPath = `${LOG_DIR}/nim-waku_${logName}.log`;
   }
 
-  async start(args?: Args) {
+  async start(args?: Args): Promise<void> {
     try {
       await existsAsync(LOG_DIR);
     } catch (e) {
@@ -116,7 +116,7 @@ export class NimWaku {
     await this.waitForLog('RPC Server started');
   }
 
-  public stop() {
+  public stop(): void {
     dbg(
       `nim-waku ${
         this.process ? this.process.pid : this.pid
@@ -126,7 +126,7 @@ export class NimWaku {
     this.process = undefined;
   }
 
-  async waitForLog(msg: string) {
+  async waitForLog(msg: string): Promise<void> {
     return waitForLine(this.logPath, msg);
   }
 
@@ -134,10 +134,10 @@ export class NimWaku {
    * for known peers
    * @throws if nim-waku2 isn't started.
    */
-  async peers() {
+  async peers(): Promise<string[]> {
     this.checkProcess();
 
-    const res = await this.rpcCall('get_waku_v2_admin_v1_peers', []);
+    const res = await this.rpcCall<string[]>('get_waku_v2_admin_v1_peers', []);
 
     return res.result;
   }
@@ -145,12 +145,15 @@ export class NimWaku {
   async info(): Promise<RpcInfoResponse> {
     this.checkProcess();
 
-    const res = await this.rpcCall('get_waku_v2_debug_v1_info', []);
+    const res = await this.rpcCall<RpcInfoResponse>(
+      'get_waku_v2_debug_v1_info',
+      []
+    );
 
     return res.result;
   }
 
-  async sendMessage(message: WakuMessage) {
+  async sendMessage(message: WakuMessage): Promise<boolean> {
     this.checkProcess();
 
     if (!message.payload) {
@@ -162,7 +165,7 @@ export class NimWaku {
       contentTopic: message.contentTopic,
     };
 
-    const res = await this.rpcCall('post_waku_v2_relay_v1_message', [
+    const res = await this.rpcCall<boolean>('post_waku_v2_relay_v1_message', [
       RelayDefaultTopic,
       rpcMessage,
     ]);
@@ -170,12 +173,13 @@ export class NimWaku {
     return res.result;
   }
 
-  async messages() {
+  async messages(): Promise<WakuMessage[]> {
     this.checkProcess();
 
-    const res = await this.rpcCall('get_waku_v2_relay_v1_messages', [
-      RelayDefaultTopic,
-    ]);
+    const res = await this.rpcCall<WakuMessage[]>(
+      'get_waku_v2_relay_v1_messages',
+      [RelayDefaultTopic]
+    );
 
     return res.result;
   }
@@ -213,10 +217,10 @@ export class NimWaku {
     return `http://localhost:${port}/`;
   }
 
-  private async rpcCall(
+  private async rpcCall<T>(
     method: string,
     params: Array<string | number | unknown>
-  ) {
+  ): Promise<{ result: T }> {
     const res = await axios.post(
       this.rpcUrl,
       {
@@ -233,7 +237,7 @@ export class NimWaku {
     return res.data;
   }
 
-  private checkProcess() {
+  private checkProcess(): void {
     if (!this.process) {
       throw "Nim Waku isn't started";
     }
@@ -282,7 +286,7 @@ export function strToHex(str: string): string {
   return hex;
 }
 
-export function bufToHex(buffer: Uint8Array) {
+export function bufToHex(buffer: Uint8Array): string {
   return Array.prototype.map
     .call(buffer, (x) => ('00' + x.toString(16)).slice(-2))
     .join('');