diff --git a/package.json b/package.json
index f9678d9..632b81c 100644
--- a/package.json
+++ b/package.json
@@ -41,7 +41,6 @@
     "abortable-iterator": "^3.0.0",
     "chai": "^4.2.0",
     "chai-checkmark": "^1.0.1",
-    "class-is": "^1.1.0",
     "debug": "^4.1.1",
     "delay": "^4.3.0",
     "detect-node": "^2.0.4",
@@ -70,7 +69,7 @@
     "aegir": "^25.0.0",
     "it-handshake": "^1.0.1",
     "rimraf": "^3.0.2",
-    "typescript": "3.7.5"
+    "typescript": "^4.1.2"
   },
   "contributors": [
     "Alan Shaw <alan.shaw@protocol.ai>",
diff --git a/src/connection/connection.d.ts b/src/connection/connection.d.ts
index f74e296..41c289f 100644
--- a/src/connection/connection.d.ts
+++ b/src/connection/connection.d.ts
@@ -1,10 +1,16 @@
-declare const _exports: typeof Connection;
-export = _exports;
+export = Connection;
 /**
  * An implementation of the js-libp2p connection.
  * Any libp2p transport should use an upgrader to return this connection.
  */
 declare class Connection {
+    /**
+     * Checks if the given value is a `Connection` instance.
+     *
+     * @param {any} other
+     * @returns {other is Connection}
+     */
+    static isConnection(other: any): other is Connection;
     /**
      * Creates an instance of Connection.
      * @param {object} properties properties of the connection.
@@ -24,10 +30,10 @@ declare class Connection {
      * @param {string} [properties.stat.encryption] connection encryption method identifier.
      */
     constructor({ localAddr, remoteAddr, localPeer, remotePeer, newStream, close, getStreams, stat }: {
-        localAddr?: import("multiaddr");
-        remoteAddr?: import("multiaddr");
-        localPeer: import("peer-id");
-        remotePeer: import("peer-id");
+        localAddr: multiaddr;
+        remoteAddr: multiaddr;
+        localPeer: PeerId;
+        remotePeer: PeerId;
         newStream: Function;
         close: Function;
         getStreams: () => any[];
@@ -37,35 +43,35 @@ declare class Connection {
                 open: string;
                 upgraded: string;
             };
-            multiplexer?: string;
-            encryption?: string;
+            multiplexer: string;
+            encryption: string;
         };
     });
     /**
      * Connection identifier.
      */
-    id: any;
+    id: string;
     /**
      * Observed multiaddr of the local peer
      */
-    localAddr: import("multiaddr");
+    localAddr: multiaddr;
     /**
      * Observed multiaddr of the remote peer
      */
-    remoteAddr: import("multiaddr");
+    remoteAddr: multiaddr;
     /**
      * Local peer id.
      */
-    localPeer: import("peer-id");
+    localPeer: PeerId;
     /**
      * Remote peer id.
      */
-    remotePeer: import("peer-id");
+    remotePeer: PeerId;
     /**
      * Connection metadata.
      */
     _stat: {
-        status: string;
+        status: "open";
         direction: string;
         timeline: {
             open: string;
@@ -95,12 +101,13 @@ declare class Connection {
      * @type {string[]}
      */
     tags: string[];
+    get [Symbol.toStringTag](): string;
     /**
      * Get connection metadata
      * @this {Connection}
      */
     get stat(): {
-        status: string;
+        status: "open";
         direction: string;
         timeline: {
             open: string;
@@ -133,7 +140,7 @@ declare class Connection {
      */
     addStream(muxedStream: any, { protocol, metadata }: {
         protocol: string;
-        metadata: any;
+        metadata: object;
     }): void;
     /**
      * Remove stream registry after it is closed.
@@ -146,4 +153,8 @@ declare class Connection {
      */
     close(): Promise<void>;
     _closing: any;
+    get [connectionSymbol](): boolean;
 }
+import multiaddr = require("multiaddr");
+import PeerId = require("peer-id");
+declare const connectionSymbol: unique symbol;
diff --git a/src/connection/status.d.ts b/src/connection/status.d.ts
index fc476fa..cef75f2 100644
--- a/src/connection/status.d.ts
+++ b/src/connection/status.d.ts
@@ -1,3 +1,3 @@
-export declare const OPEN: string;
-export declare const CLOSING: string;
-export declare const CLOSED: string;
+export const OPEN: 'open';
+export const CLOSING: 'closing';
+export const CLOSED: 'closed';
diff --git a/src/pubsub/errors.d.ts b/src/pubsub/errors.d.ts
index 4bbf5b3..b5349d1 100644
--- a/src/pubsub/errors.d.ts
+++ b/src/pubsub/errors.d.ts
@@ -1,11 +1,11 @@
 export namespace codes {
-    export const ERR_INVALID_SIGNATURE_POLICY: string;
-    export const ERR_UNHANDLED_SIGNATURE_POLICY: string;
-    export const ERR_MISSING_SIGNATURE: string;
-    export const ERR_MISSING_SEQNO: string;
-    export const ERR_INVALID_SIGNATURE: string;
-    export const ERR_UNEXPECTED_FROM: string;
-    export const ERR_UNEXPECTED_SIGNATURE: string;
-    export const ERR_UNEXPECTED_KEY: string;
-    export const ERR_UNEXPECTED_SEQNO: string;
+    const ERR_INVALID_SIGNATURE_POLICY: string;
+    const ERR_UNHANDLED_SIGNATURE_POLICY: string;
+    const ERR_MISSING_SIGNATURE: string;
+    const ERR_MISSING_SEQNO: string;
+    const ERR_INVALID_SIGNATURE: string;
+    const ERR_UNEXPECTED_FROM: string;
+    const ERR_UNEXPECTED_SIGNATURE: string;
+    const ERR_UNEXPECTED_KEY: string;
+    const ERR_UNEXPECTED_SEQNO: string;
 }
diff --git a/src/pubsub/index.d.ts b/src/pubsub/index.d.ts
index f2a8d1c..a327bf7 100644
--- a/src/pubsub/index.d.ts
+++ b/src/pubsub/index.d.ts
@@ -29,11 +29,14 @@ declare class PubsubBaseProtocol {
      */
     constructor({ debugName, multicodecs, libp2p, globalSignaturePolicy, canRelayMessage, emitSelf }: {
         debugName: string;
-        multicodecs: string | string[];
+        multicodecs: Array<string> | string;
         libp2p: any;
-        globalSignaturePolicy?: any;
-        canRelayMessage?: boolean;
-        emitSelf?: boolean;
+        globalSignaturePolicy: {
+            StrictSign: "StrictSign";
+            StrictNoSign: string;
+        };
+        canRelayMessage: boolean;
+        emitSelf: boolean;
     });
     log: any;
     /**
@@ -91,7 +94,7 @@ declare class PubsubBaseProtocol {
      * Topic validators are functions with the following input:
      * @type {Map<string, validator>}
      */
-    topicValidators: Map<string, validator>;
+    topicValidators: Map<string, (arg0: string, arg1: InMessage) => Promise<void>>;
     _registrarId: any;
     /**
      * On an inbound stream opened.
@@ -101,25 +104,21 @@ declare class PubsubBaseProtocol {
      * @param {DuplexIterableStream} props.stream
      * @param {Connection} props.connection connection
      */
-    _onIncomingStream({ protocol, stream, connection }: {
-        protocol: string;
-        stream: any;
-        connection: any;
-    }): void;
+    private _onIncomingStream;
     /**
      * Registrar notifies an established connection with pubsub protocol.
      * @private
      * @param {PeerId} peerId remote peer-id
      * @param {Connection} conn connection to the peer
      */
-    _onPeerConnected(peerId: import("peer-id"), conn: any): Promise<void>;
+    private _onPeerConnected;
     /**
      * Registrar notifies a closing connection with pubsub protocol.
      * @private
      * @param {PeerId} peerId peerId
      * @param {Error} err error for connection end
      */
-    _onPeerDisconnected(peerId: import("peer-id"), err: Error): void;
+    private _onPeerDisconnected;
     /**
      * Register the pubsub protocol onto the libp2p node.
      * @returns {void}
@@ -137,14 +136,14 @@ declare class PubsubBaseProtocol {
      * @param {string} protocol
      * @returns {PeerStreams}
      */
-    _addPeer(peerId: import("peer-id"), protocol: string): import("./peer-streams");
+    private _addPeer;
     /**
      * Notifies the router that a peer has been disconnected.
      * @private
      * @param {PeerId} peerId
      * @returns {PeerStreams | undefined}
      */
-    _removePeer(peerId: import("peer-id")): import("./peer-streams");
+    private _removePeer;
     /**
      * Responsible for processing each RPC message received by other peers.
      * @param {string} idB58Str peer id string in base58
@@ -152,7 +151,7 @@ declare class PubsubBaseProtocol {
      * @param {PeerStreams} peerStreams PubSub peer
      * @returns {Promise<void>}
      */
-    _processMessages(idB58Str: string, stream: any, peerStreams: import("./peer-streams")): Promise<void>;
+    _processMessages(idB58Str: string, stream: any, peerStreams: PeerStreams): Promise<void>;
     /**
      * Handles an rpc request from a peer
      * @param {String} idB58Str
@@ -160,7 +159,7 @@ declare class PubsubBaseProtocol {
      * @param {RPC} rpc
      * @returns {boolean}
      */
-    _processRpc(idB58Str: string, peerStreams: import("./peer-streams"), rpc: any): boolean;
+    _processRpc(idB58Str: string, peerStreams: PeerStreams, rpc: any): boolean;
     /**
      * Handles a subscription change from a peer
      * @param {string} id
@@ -236,13 +235,13 @@ declare class PubsubBaseProtocol {
      * @param {Message} message
      * @returns {Promise<Message>}
      */
-    _buildMessage(message: any): Promise<any>;
+    private _buildMessage;
     /**
      * Get a list of the peer-ids that are subscribed to one topic.
      * @param {string} topic
      * @returns {Array<string>}
      */
-    getSubscribers(topic: string): string[];
+    getSubscribers(topic: string): Array<string>;
     /**
      * Publishes messages to all subscribed peers
      * @override
@@ -279,16 +278,12 @@ declare class PubsubBaseProtocol {
      * @override
      * @returns {Array<String>}
      */
-    getTopics(): string[];
+    getTopics(): Array<string>;
 }
 declare namespace PubsubBaseProtocol {
     export { message, utils, SignaturePolicy, InMessage, PeerId };
 }
 type PeerId = import("peer-id");
-/**
- * Topic validator function
- */
-type validator = (arg0: string, arg1: InMessage) => Promise<void>;
 type InMessage = {
     from?: string;
     receivedFrom: string;
@@ -298,12 +293,10 @@ type InMessage = {
     signature?: Uint8Array;
     key?: Uint8Array;
 };
+import PeerStreams = require("./peer-streams");
 /**
  * @type {typeof import('./message')}
  */
 declare const message: typeof import('./message');
-declare const utils: typeof import("./utils");
-declare const SignaturePolicy: {
-    StrictSign: string;
-    StrictNoSign: string;
-};
+import utils = require("./utils");
+import { SignaturePolicy } from "./signature-policy";
diff --git a/src/pubsub/message/index.d.ts b/src/pubsub/message/index.d.ts
index 62df1ce..de14b7b 100644
--- a/src/pubsub/message/index.d.ts
+++ b/src/pubsub/message/index.d.ts
@@ -1,5 +1,4 @@
-export var rpc: any;
-export var td: any;
-export var RPC: any;
-export var Message: any;
-export var SubOpts: any;
+declare const rpcProto: any;
+declare const topicDescriptorProto: any;
+export const RPC: any;
+export { rpcProto as rpc, topicDescriptorProto as td };
diff --git a/src/pubsub/message/sign.d.ts b/src/pubsub/message/sign.d.ts
index 3e1bee2..0750e01 100644
--- a/src/pubsub/message/sign.d.ts
+++ b/src/pubsub/message/sign.d.ts
@@ -13,7 +13,7 @@ export function messagePublicKey(message: any): Promise<any>;
  * @param {Message} message
  * @returns {Promise<Message>}
  */
-export function signMessage(peerId: import("peer-id"), message: any): Promise<any>;
+export function signMessage(peerId: PeerId, message: any): Promise<any>;
 export const SignPrefix: any;
 /**
  * Verifies the signature of the given message
@@ -21,3 +21,4 @@ export const SignPrefix: any;
  * @returns {Promise<Boolean>}
  */
 export function verifySignature(message: any): Promise<boolean>;
+import PeerId = require("peer-id");
diff --git a/src/pubsub/peer-streams.d.ts b/src/pubsub/peer-streams.d.ts
index 632fe2c..00d1523 100644
--- a/src/pubsub/peer-streams.d.ts
+++ b/src/pubsub/peer-streams.d.ts
@@ -21,7 +21,7 @@ declare class PeerStreams {
      * @param {string} properties.protocol
      */
     constructor({ id, protocol }: {
-        id: import("peer-id");
+        id: PeerId;
         protocol: string;
     });
     /**
@@ -38,19 +38,19 @@ declare class PeerStreams {
      * @private
      * @type {DuplexIterableStream}
      */
-    _rawOutboundStream: DuplexIterableStream;
+    private _rawOutboundStream;
     /**
      * The raw inbound stream, as retrieved from the callback from libp2p.handle
      * @private
      * @type {DuplexIterableStream}
      */
-    _rawInboundStream: DuplexIterableStream;
+    private _rawInboundStream;
     /**
      * An AbortController for controlled shutdown of the inbound stream
      * @private
      * @type {typeof AbortController}
      */
-    _inboundAbortController: typeof AbortController;
+    private _inboundAbortController;
     /**
      * Write stream -- its preferable to use the write method
      * @type {import('it-pushable').Pushable<Uint8Array>>}
@@ -106,8 +106,7 @@ declare namespace PeerStreams {
 }
 type DuplexIterableStream = {
     sink: Sink;
-    source: () => AsyncIterator<Uint8Array, any, undefined>;
+    source: () => AsyncIterator<Uint8Array>;
 };
-declare const AbortController: typeof import("abort-controller");
-type Sink = (source: Uint8Array) => Promise<Uint8Array>;
 type PeerId = import("peer-id");
+type Sink = (source: Uint8Array) => Promise<Uint8Array>;
diff --git a/src/pubsub/signature-policy.d.ts b/src/pubsub/signature-policy.d.ts
index cf04e15..f8b07a1 100644
--- a/src/pubsub/signature-policy.d.ts
+++ b/src/pubsub/signature-policy.d.ts
@@ -1,4 +1,4 @@
 export namespace SignaturePolicy {
-    export const StrictSign: string;
-    export const StrictNoSign: string;
+    const StrictSign: 'StrictSign';
+    const StrictNoSign: string;
 }
diff --git a/src/pubsub/utils.d.ts b/src/pubsub/utils.d.ts
index f0ae093..1cc14a4 100644
--- a/src/pubsub/utils.d.ts
+++ b/src/pubsub/utils.d.ts
@@ -1,7 +1,13 @@
 export function randomSeqno(): Uint8Array;
 export function msgId(from: string, seqno: Uint8Array): Uint8Array;
 export function noSignMsgId(data: Uint8Array): Uint8Array;
-export function anyMatch(a: any[] | Set<any>, b: any[] | Set<any>): boolean;
-export function ensureArray(maybeArray: any): any[];
-export function normalizeInRpcMessage(message: any, peerId: string): any;
-export function normalizeOutRpcMessage(message: any): any;
+export function anyMatch(a: Set<any> | any[], b: Set<any> | any[]): boolean;
+export function ensureArray<T>(maybeArray: T | T[]): T[];
+export function normalizeInRpcMessage<T extends unknown>(message: T, peerId?: string): T & {
+    from?: string;
+    peerId?: string;
+};
+export function normalizeOutRpcMessage<T extends unknown>(message: T): T & {
+    from?: Uint8Array;
+    data?: Uint8Array;
+};
diff --git a/src/topology/index.d.ts b/src/topology/index.d.ts
index d2e1141..70241f4 100644
--- a/src/topology/index.d.ts
+++ b/src/topology/index.d.ts
@@ -1,10 +1,16 @@
-declare const _exports: Topology;
-export = _exports;
+export = Topology;
 declare class Topology {
+    /**
+     * Checks if the given value is a Topology instance.
+     *
+     * @param {any} other
+     * @returns {other is Topology}
+     */
+    static isTopology(other: any): other is Topology;
     /**
      * @param {Object} props
-     * @param {number} props.min minimum needed connections (default: 0)
-     * @param {number} props.max maximum needed connections (default: Infinity)
+     * @param {number} [props.min] minimum needed connections (default: 0)
+     * @param {number} [props.max] maximum needed connections (default: Infinity)
      * @param {Object} [props.handlers]
      * @param {function} [props.handlers.onConnect] protocol "onConnect" handler
      * @param {function} [props.handlers.onDisconnect] protocol "onDisconnect" handler
@@ -13,9 +19,9 @@ declare class Topology {
     constructor({ min, max, handlers }: {
         min: number;
         max: number;
-        handlers?: {
-            onConnect?: Function;
-            onDisconnect?: Function;
+        handlers: {
+            onConnect: Function;
+            onDisconnect: Function;
         };
     });
     min: number;
@@ -27,6 +33,7 @@ declare class Topology {
      * @type {Set<string>}
      */
     peers: Set<string>;
+    get [Symbol.toStringTag](): string;
     set registrar(arg: any);
     _registrar: any;
     /**
@@ -39,4 +46,6 @@ declare class Topology {
      * @returns {void}
      */
     disconnect(peerId: import("peer-id")): void;
+    get [topologySymbol](): boolean;
 }
+declare const topologySymbol: unique symbol;
diff --git a/src/topology/multicodec-topology.d.ts b/src/topology/multicodec-topology.d.ts
index 2038926..06d16f5 100644
--- a/src/topology/multicodec-topology.d.ts
+++ b/src/topology/multicodec-topology.d.ts
@@ -1,5 +1,12 @@
 export = MulticodecTopology;
-declare class MulticodecTopology {
+declare class MulticodecTopology extends Topology {
+    /**
+     * Checks if the given value is a `MulticodecTopology` instance.
+     *
+     * @param {any} other
+     * @returns {other is MulticodecTopology}
+     */
+    static isMulticodecTopology(other: any): other is MulticodecTopology;
     /**
      * @param {Object} props
      * @param {number} [props.min] minimum needed connections (default: 0)
@@ -11,16 +18,15 @@ declare class MulticodecTopology {
      * @constructor
      */
     constructor({ min, max, multicodecs, handlers }: {
-        min?: number;
-        max?: number;
-        multicodecs: string[];
+        min: number;
+        max: number;
+        multicodecs: Array<string>;
         handlers: {
             onConnect: Function;
             onDisconnect: Function;
         };
     });
     multicodecs: string[];
-    _registrar: any;
     /**
      * Check if a new peer support the multicodecs for this topology.
      * @param {Object} props
@@ -29,7 +35,7 @@ declare class MulticodecTopology {
      */
     _onProtocolChange({ peerId, protocols }: {
         peerId: any;
-        protocols: string[];
+        protocols: Array<string>;
     }): void;
     /**
      * Verify if a new connected peer has a topology multicodec and call _onConnect.
@@ -37,15 +43,17 @@ declare class MulticodecTopology {
      * @returns {void}
      */
     _onPeerConnect(connection: any): void;
-    set registrar(arg: any);
     /**
      * Update topology.
      * @param {Array<{id: PeerId, multiaddrs: Array<Multiaddr>, protocols: Array<string>}>} peerDataIterable
      * @returns {void}
      */
-    _updatePeers(peerDataIterable: {
+    _updatePeers(peerDataIterable: Array<{
         id: any;
-        multiaddrs: any[];
-        protocols: string[];
-    }[]): void;
+        multiaddrs: Array<any>;
+        protocols: Array<string>;
+    }>): void;
+    get [multicodecTopologySymbol](): boolean;
 }
+import Topology = require(".");
+declare const multicodecTopologySymbol: unique symbol;