diff --git a/packages/fcl-core/src/wallet-utils/CompositeSignature.js b/packages/fcl-core/src/wallet-utils/CompositeSignature.js
deleted file mode 100644
index 5450c596e..000000000
--- a/packages/fcl-core/src/wallet-utils/CompositeSignature.js
+++ /dev/null
@@ -1,18 +0,0 @@
-import {withPrefix} from "@onflow/util-address"
-import {COMPOSITE_SIGNATURE_PRAGMA} from "../normalizers/service/__vsn"
-
-/**
- * @description
- * Constructs a new CompositeSignature instance.
- *
- * @param {string} addr - Flow Address
- * @param {number} keyId - Key ID
- * @param {string} signature - Signature as a hex string
- */
-export function CompositeSignature(addr, keyId, signature) {
-  this.f_type = COMPOSITE_SIGNATURE_PRAGMA.f_type
-  this.f_vsn = COMPOSITE_SIGNATURE_PRAGMA.f_vsn
-  this.addr = withPrefix(addr)
-  this.keyId = Number(keyId)
-  this.signature = signature
-}
diff --git a/packages/fcl-core/src/wallet-utils/CompositeSignature.ts b/packages/fcl-core/src/wallet-utils/CompositeSignature.ts
new file mode 100644
index 000000000..82085e1bf
--- /dev/null
+++ b/packages/fcl-core/src/wallet-utils/CompositeSignature.ts
@@ -0,0 +1,25 @@
+import {withPrefix} from "@onflow/util-address"
+import {COMPOSITE_SIGNATURE_PRAGMA} from "../normalizers/service/__vsn"
+
+/**
+ * @description Constructs a new CompositeSignature instance.
+ *
+ * @param addr Flow Address
+ * @param keyId Key ID
+ * @param signature Signature as a hex string
+ */
+export class CompositeSignature {
+  f_type: string
+  f_vsn: string
+  addr: string
+  keyId: number
+  signature: string
+
+  constructor(addr: string, keyId: number | string, signature: string) {
+    this.f_type = COMPOSITE_SIGNATURE_PRAGMA.f_type
+    this.f_vsn = COMPOSITE_SIGNATURE_PRAGMA.f_vsn
+    this.addr = withPrefix(addr)
+    this.keyId = Number(keyId)
+    this.signature = signature
+  }
+}
diff --git a/packages/fcl-core/src/wallet-utils/encode-account-proof.test.js b/packages/fcl-core/src/wallet-utils/encode-account-proof.test.ts
similarity index 96%
rename from packages/fcl-core/src/wallet-utils/encode-account-proof.test.js
rename to packages/fcl-core/src/wallet-utils/encode-account-proof.test.ts
index 471adce93..60a5adb08 100644
--- a/packages/fcl-core/src/wallet-utils/encode-account-proof.test.js
+++ b/packages/fcl-core/src/wallet-utils/encode-account-proof.test.ts
@@ -1,4 +1,4 @@
-import {encodeAccountProof} from "./encode-account-proof.js"
+import {encodeAccountProof} from "./encode-account-proof"
 
 const address = "0xABC123DEF456"
 const appIdentifier = "AWESOME-APP-ID"
diff --git a/packages/fcl-core/src/wallet-utils/encode-account-proof.js b/packages/fcl-core/src/wallet-utils/encode-account-proof.ts
similarity index 59%
rename from packages/fcl-core/src/wallet-utils/encode-account-proof.js
rename to packages/fcl-core/src/wallet-utils/encode-account-proof.ts
index 0b01477a2..e6bbb08bf 100644
--- a/packages/fcl-core/src/wallet-utils/encode-account-proof.js
+++ b/packages/fcl-core/src/wallet-utils/encode-account-proof.ts
@@ -2,35 +2,41 @@ import {sansPrefix} from "@onflow/util-address"
 import {invariant} from "@onflow/util-invariant"
 import {Buffer, encode as rlpEncode} from "@onflow/rlp"
 
-const rightPaddedHexBuffer = (value, pad) =>
+export interface AccountProofData {
+  address?: string
+  nonce?: string
+  appIdentifier?: string
+}
+
+const rightPaddedHexBuffer = (value: string, pad: number): Buffer =>
   Buffer.from(value.padEnd(pad * 2, "0"), "hex")
 
-const leftPaddedHexBuffer = (value, pad) =>
+const leftPaddedHexBuffer = (value: string, pad: number): Buffer =>
   Buffer.from(value.padStart(pad * 2, "0"), "hex")
 
-const addressBuffer = addr => leftPaddedHexBuffer(addr, 8)
+const addressBuffer = (addr: string): Buffer => leftPaddedHexBuffer(addr, 8)
 
-const nonceBuffer = nonce => Buffer.from(nonce, "hex")
+const nonceBuffer = (nonce: string): Buffer => Buffer.from(nonce, "hex")
 
 export const encodeAccountProof = (
-  {address, nonce, appIdentifier},
-  includeDomainTag = true
-) => {
+  {address, nonce, appIdentifier}: AccountProofData,
+  includeDomainTag: boolean = true
+): string => {
   invariant(
-    address,
+    !!address,
     "Encode Message For Provable Authn Error: address must be defined"
   )
   invariant(
-    nonce,
+    !!nonce,
     "Encode Message For Provable Authn Error: nonce must be defined"
   )
   invariant(
-    appIdentifier,
+    !!appIdentifier,
     "Encode Message For Provable Authn Error: appIdentifier must be defined"
   )
 
   invariant(
-    nonce.length >= 64,
+    nonce!.length >= 64,
     "Encode Message For Provable Authn Error: nonce must be minimum of 32 bytes"
   )
 
@@ -44,15 +50,15 @@ export const encodeAccountProof = (
       ACCOUNT_PROOF_DOMAIN_TAG,
       rlpEncode([
         appIdentifier,
-        addressBuffer(sansPrefix(address)),
-        nonceBuffer(nonce),
+        addressBuffer(sansPrefix(address!)),
+        nonceBuffer(nonce!),
       ]),
     ]).toString("hex")
   }
 
   return rlpEncode([
     appIdentifier,
-    addressBuffer(sansPrefix(address)),
-    nonceBuffer(nonce),
+    addressBuffer(sansPrefix(address!)),
+    nonceBuffer(nonce!),
   ]).toString("hex")
 }
diff --git a/packages/fcl-core/src/wallet-utils/index.js b/packages/fcl-core/src/wallet-utils/index.js
deleted file mode 100644
index 1757de831..000000000
--- a/packages/fcl-core/src/wallet-utils/index.js
+++ /dev/null
@@ -1,13 +0,0 @@
-export {
-  sendMsgToFCL,
-  ready,
-  close,
-  approve,
-  decline,
-  redirect,
-} from "./send-msg-to-fcl.js"
-export {onMessageFromFCL} from "./on-message-from-fcl.js"
-export {encodeMessageFromSignable} from "@onflow/sdk"
-export {CompositeSignature} from "./CompositeSignature.js"
-export {encodeAccountProof} from "./encode-account-proof.js"
-export {injectExtService} from "./inject-ext-service.js"
diff --git a/packages/fcl-core/src/wallet-utils/index.ts b/packages/fcl-core/src/wallet-utils/index.ts
new file mode 100644
index 000000000..a37d0051d
--- /dev/null
+++ b/packages/fcl-core/src/wallet-utils/index.ts
@@ -0,0 +1,13 @@
+export {
+  sendMsgToFCL,
+  ready,
+  close,
+  approve,
+  decline,
+  redirect,
+} from "./send-msg-to-fcl"
+export {onMessageFromFCL} from "./on-message-from-fcl"
+export {encodeMessageFromSignable} from "@onflow/sdk"
+export {CompositeSignature} from "./CompositeSignature"
+export {encodeAccountProof} from "./encode-account-proof"
+export {injectExtService} from "./inject-ext-service"
diff --git a/packages/fcl-core/src/wallet-utils/inject-ext-service.js b/packages/fcl-core/src/wallet-utils/inject-ext-service.js
deleted file mode 100644
index b5c607707..000000000
--- a/packages/fcl-core/src/wallet-utils/inject-ext-service.js
+++ /dev/null
@@ -1,10 +0,0 @@
-export function injectExtService(service) {
-  if (service.type === "authn" && service.endpoint != null) {
-    if (!Array.isArray(window.fcl_extensions)) {
-      window.fcl_extensions = []
-    }
-    window.fcl_extensions.push(service)
-  } else {
-    console.warn("Authn service is required")
-  }
-}
diff --git a/packages/fcl-core/src/wallet-utils/inject-ext-service.ts b/packages/fcl-core/src/wallet-utils/inject-ext-service.ts
new file mode 100644
index 000000000..e3b82481c
--- /dev/null
+++ b/packages/fcl-core/src/wallet-utils/inject-ext-service.ts
@@ -0,0 +1,12 @@
+import type {Service} from "@onflow/typedefs"
+
+export function injectExtService(service: Service): void {
+  if (service.type === "authn" && service.endpoint != null) {
+    if (!Array.isArray((window as any).fcl_extensions)) {
+      ;(window as any).fcl_extensions = []
+    }
+    ;(window as any).fcl_extensions.push(service)
+  } else {
+    console.warn("Authn service is required")
+  }
+}
diff --git a/packages/fcl-core/src/wallet-utils/on-message-from-fcl.js b/packages/fcl-core/src/wallet-utils/on-message-from-fcl.ts
similarity index 59%
rename from packages/fcl-core/src/wallet-utils/on-message-from-fcl.js
rename to packages/fcl-core/src/wallet-utils/on-message-from-fcl.ts
index 585269fe2..18dff7b65 100644
--- a/packages/fcl-core/src/wallet-utils/on-message-from-fcl.js
+++ b/packages/fcl-core/src/wallet-utils/on-message-from-fcl.ts
@@ -2,12 +2,15 @@
  * @description
  * Listens for messages from FCL
  *
- * @param {string} messageType - Message type
- * @param {Function} cb - Callback function
- * @returns {Function} - Function to remove event listener
+ * @param messageType Message type
+ * @param cb Callback function
+ * @returns Function to remove event listener
  */
-export const onMessageFromFCL = (messageType, cb = () => {}) => {
-  const buildData = data => {
+export const onMessageFromFCL = (
+  messageType: string,
+  cb: (data: any, context: {origin: string}) => void = () => {}
+): (() => void) => {
+  const buildData = (data: any): any => {
     if (data.deprecated)
       console.warn("DEPRECATION NOTICE", data.deprecated.message)
     delete data?.body?.interaction
@@ -15,7 +18,7 @@ export const onMessageFromFCL = (messageType, cb = () => {}) => {
     return data
   }
 
-  const internal = e => {
+  const internal = (e: MessageEvent): void => {
     const {data, origin} = e
     if (typeof data !== "object") return
     if (typeof data == null) return
diff --git a/packages/fcl-core/src/wallet-utils/send-msg-to-fcl.js b/packages/fcl-core/src/wallet-utils/send-msg-to-fcl.ts
similarity index 58%
rename from packages/fcl-core/src/wallet-utils/send-msg-to-fcl.js
rename to packages/fcl-core/src/wallet-utils/send-msg-to-fcl.ts
index 2362dc177..5b57528be 100644
--- a/packages/fcl-core/src/wallet-utils/send-msg-to-fcl.js
+++ b/packages/fcl-core/src/wallet-utils/send-msg-to-fcl.ts
@@ -3,15 +3,20 @@ import {
   FCL_RESPONSE_PARAM_NAME,
 } from "../utils/constants"
 import {onMessageFromFCL} from "./on-message-from-fcl"
-import {URL} from "../utils/url"
+
+export interface PollingResponse {
+  f_type: "PollingResponse"
+  f_vsn: "1.0.0"
+  status: "APPROVED" | "DECLINED" | "REDIRECT"
+  reason: string | null
+  data: any
+}
 
 /**
- * @description
- * Sends message to FCL window
+ * @description Sends message to FCL window
  *
- * @param {string} type - Message type
- * @param {object} msg - Message object
- * @returns {void}
+ * @param type Message type
+ * @param msg Message object
  *
  * @example
  * sendMsgToFCL("FCL:VIEW:RESPONSE", {
@@ -22,7 +27,7 @@ import {URL} from "../utils/url"
  *    data: data,
  *  })
  */
-export const sendMsgToFCL = (type, msg = {}) => {
+export const sendMsgToFCL = (type: string, msg?: PollingResponse): void => {
   const data = {...msg, type}
 
   const urlParams = new URLSearchParams(window.location.search)
@@ -41,36 +46,32 @@ export const sendMsgToFCL = (type, msg = {}) => {
 }
 
 /**
- * @description
- * Listens for "FCL:VIEW:READY:RESPONSE" and sends "FCL:VIEW:READY"
+ * @description Listens for "FCL:VIEW:READY:RESPONSE" and sends "FCL:VIEW:READY"
  *
- * @param {Function} cb - Callback function
- * @param {object} msg - Message object
- * @returns {void}
+ * @param cb Callback function
+ * @param msg Message object
  */
-export const ready = (cb, msg = {}) => {
+export const ready = (
+  cb: (data: any, context: {origin: string}) => void,
+  msg: PollingResponse = {} as PollingResponse
+): void => {
   onMessageFromFCL("FCL:VIEW:READY:RESPONSE", cb)
   sendMsgToFCL("FCL:VIEW:READY")
 }
 
 /**
- * @description
- * Sends "FCL:VIEW:CLOSE"
- *
- * @returns {void}
+ * @description Sends "FCL:VIEW:CLOSE"
  */
-export const close = () => {
+export const close = (): void => {
   sendMsgToFCL("FCL:VIEW:CLOSE")
 }
 
 /**
- * @description
- * Sends "FCL:VIEW:RESPONSE" with status "APPROVED"
+ * @description Sends "FCL:VIEW:RESPONSE" with status "APPROVED"
  *
- * @param {object} data - Data object
- * @returns {void}
+ * @param data Data object
  */
-export const approve = data => {
+export const approve = (data: any): void => {
   sendMsgToFCL("FCL:VIEW:RESPONSE", {
     f_type: "PollingResponse",
     f_vsn: "1.0.0",
@@ -81,13 +82,11 @@ export const approve = data => {
 }
 
 /**
- * @description
- * Sends "FCL:VIEW:RESPONSE" with status "DECLINED"
+ * @description Sends "FCL:VIEW:RESPONSE" with status "DECLINED"
  *
- * @param {string} reason - Reason for declining
- * @returns {void}
+ * @param reason Reason for declining
  */
-export const decline = reason => {
+export const decline = (reason: string): void => {
   sendMsgToFCL("FCL:VIEW:RESPONSE", {
     f_type: "PollingResponse",
     f_vsn: "1.0.0",
@@ -98,13 +97,11 @@ export const decline = reason => {
 }
 
 /**
- * @description
- * Sends "FCL:VIEW:RESPONSE" with status "REDIRECT"
+ * @description Sends "FCL:VIEW:RESPONSE" with status "REDIRECT"
  *
- * @param {object} data - Data object
- * @returns {void}
+ * @param data Data object
  */
-export const redirect = data => {
+export const redirect = (data: any): void => {
   sendMsgToFCL("FCL:VIEW:RESPONSE", {
     f_type: "PollingResponse",
     f_vsn: "1.0.0",
diff --git a/packages/fcl-core/src/wallet-utils/wallet-utils.test.js b/packages/fcl-core/src/wallet-utils/wallet-utils.test.ts
similarity index 100%
rename from packages/fcl-core/src/wallet-utils/wallet-utils.test.js
rename to packages/fcl-core/src/wallet-utils/wallet-utils.test.ts