diff --git a/tests/extensions/base64ext.nim b/tests/extensions/base64ext.nim
new file mode 100644
index 0000000..35c0753
--- /dev/null
+++ b/tests/extensions/base64ext.nim
@@ -0,0 +1,120 @@
+## nim-ws
+## Copyright (c) 2021 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import
+  std/[strutils],
+  pkg/[stew/results,
+    stew/base64,
+    chronos,
+    chronicles],
+  ../../ws/types,
+  ../../ws/frame
+
+type
+  Base64Ext = ref object of Ext
+    padding: bool
+    transform: bool
+
+const
+  extID = "base64"
+
+method decode(ext: Base64Ext, frame: Frame): Future[Frame] {.async.} =
+  if frame.opcode notin {Opcode.Text, Opcode.Binary, Opcode.Cont}:
+    return frame
+
+  if frame.opcode in {Opcode.Text, Opcode.Binary}:
+    ext.transform = frame.rsv2
+    frame.rsv2 = false
+
+  if not ext.transform:
+    return frame
+
+  if frame.length > 0:
+    var data: seq[byte]
+    var buf: array[0xFFFF, byte]
+
+    while data.len < frame.length.int:
+      let len = min(frame.length.int - data.len, buf.len)
+      let read = await frame.read(ext.session.stream.reader, addr buf[0], len)
+      data.add toOpenArray(buf, 0, read - 1)
+
+      if data.len > ext.session.frameSize:
+        raise newException(WSPayloadTooLarge, "payload exceeds allowed max frame size")
+
+    # bug in Base64.Decode when accepts seq[byte]
+    let instr = cast[string](data)
+    if ext.padding:
+      frame.data = Base64Pad.decode(instr)
+    else:
+      frame.data = Base64.decode(instr)
+
+    trace "Base64Ext decode", input=frame.length, output=frame.data.len
+
+    frame.length = frame.data.len.uint64
+    frame.offset = 0
+    frame.consumed = 0
+    frame.mask = false
+
+  return frame
+
+method encode(ext: Base64Ext, frame: Frame): Future[Frame] {.async.} =
+  if frame.opcode notin {Opcode.Text, Opcode.Binary, Opcode.Cont}:
+    return frame
+
+  if frame.opcode in {Opcode.Text, Opcode.Binary}:
+    ext.transform = true
+    frame.rsv2 = ext.transform
+
+  if not ext.transform:
+    return frame
+
+  frame.length = frame.data.len.uint64
+
+  if ext.padding:
+    frame.data = cast[seq[byte]](Base64Pad.encode(frame.data))
+  else:
+    frame.data = cast[seq[byte]](Base64.encode(frame.data))
+
+  trace "Base64Ext encode", input=frame.length, output=frame.data.len
+
+  frame.length = frame.data.len.uint64
+  frame.offset = 0
+  frame.consumed = 0
+
+  return frame
+
+method toHttpOptions(ext: Base64Ext): string =
+  extID & "; pad=" & $ext.padding
+
+proc base64Factory*(padding: bool): ExtFactory =
+
+  proc factory(isServer: bool,
+       args: seq[ExtParam]): Result[Ext, string] {.
+       gcsafe, raises: [Defect].} =
+
+    # you can capture configuration variables via closure
+    # if you want
+
+    var ext = Base64Ext(
+      name     : extID,
+      transform: false
+    )
+
+    for arg in args:
+      if arg.name == "pad":
+        ext.padding = arg.value == "true"
+        break
+
+    ok(ext)
+
+  ExtFactory(
+    name: extID,
+    factory: factory,
+    clientOffer: extID & "; pad=" & $padding
+  )
diff --git a/tests/extensions/hexext.nim b/tests/extensions/hexext.nim
new file mode 100644
index 0000000..32ade7c
--- /dev/null
+++ b/tests/extensions/hexext.nim
@@ -0,0 +1,103 @@
+## nim-ws
+## Copyright (c) 2021 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import
+  std/[strutils],
+  pkg/[stew/results,
+    stew/byteutils,
+    chronos,
+    chronicles],
+  ../../ws/types,
+  ../../ws/frame
+
+type
+  HexExt = ref object of Ext
+    transform: bool
+
+const
+  extID = "hex"
+
+method decode(ext: HexExt, frame: Frame): Future[Frame] {.async.} =
+  if frame.opcode notin {Opcode.Text, Opcode.Binary, Opcode.Cont}:
+    return frame
+
+  if frame.opcode in {Opcode.Text, Opcode.Binary}:
+    ext.transform = frame.rsv3
+    frame.rsv3 = false
+
+  if not ext.transform:
+    return frame
+
+  if frame.length > 0:
+    var data: seq[byte]
+    var buf: array[0xFFFF, byte]
+
+    while data.len < frame.length.int:
+      let len = min(frame.length.int - data.len, buf.len)
+      let read = await frame.read(ext.session.stream.reader, addr buf[0], len)
+      data.add toOpenArray(buf, 0, read - 1)
+
+      if data.len > ext.session.frameSize:
+        raise newException(WSPayloadTooLarge, "payload exceeds allowed max frame size")
+
+    frame.data = hexToSeqByte(cast[string](data))
+    trace "HexExt decode", input=frame.length, output=frame.data.len
+
+    frame.length = frame.data.len.uint64
+    frame.offset = 0
+    frame.consumed = 0
+    frame.mask = false
+
+  return frame
+
+method encode(ext: HexExt, frame: Frame): Future[Frame] {.async.} =
+  if frame.opcode notin {Opcode.Text, Opcode.Binary, Opcode.Cont}:
+    return frame
+
+  if frame.opcode in {Opcode.Text, Opcode.Binary}:
+    ext.transform = true
+    frame.rsv3 = ext.transform
+
+  if not ext.transform:
+    return frame
+
+  frame.length = frame.data.len.uint64
+  frame.data = cast[seq[byte]](toHex(frame.data))
+  trace "HexExt encode", input=frame.length, output=frame.data.len
+
+  frame.length = frame.data.len.uint64
+  frame.offset = 0
+  frame.consumed = 0
+
+  return frame
+
+method toHttpOptions(ext: HexExt): string =
+  extID
+
+proc hexFactory*(): ExtFactory =
+
+  proc factory(isServer: bool,
+       args: seq[ExtParam]): Result[Ext, string] {.
+       gcsafe, raises: [Defect].} =
+
+    # you can capture configuration variables via closure
+    # if you want
+
+    var ext = HexExt(
+      name     : extID,
+      transform: false
+    )
+
+    ok(ext)
+
+  ExtFactory(
+    name: extID,
+    factory: factory,
+    clientOffer: extID
+  )
diff --git a/tests/extensions/testexts.nim b/tests/extensions/testexts.nim
new file mode 100644
index 0000000..4fe5a18
--- /dev/null
+++ b/tests/extensions/testexts.nim
@@ -0,0 +1,89 @@
+## nim-ws
+## Copyright (c) 2021 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import pkg/[chronos, stew/byteutils]
+import ../asyncunit
+import ./base64ext, ./hexext
+import ../../ws/ws, ../helpers
+
+suite "UTF-8 validator in action":
+  var server: HttpServer
+  let address = initTAddress("127.0.0.1:8888")
+  let hexFactory = hexFactory()
+  let base64Factory = base64Factory(padding = true)
+
+  teardown:
+    server.stop()
+    await server.closeWait()
+
+  test "hex to base64 ext flow":
+    let testData = "hello world"
+    proc handle(request: HttpRequest) {.async.} =
+      let server = WSServer.new(
+        protos = ["proto"],
+        factories = [hexFactory, base64Factory],
+      )
+      let ws = await server.handleRequest(request)
+      let recvData = await ws.recv()
+      await ws.send(recvData,
+        if ws.binary: Opcode.Binary else: Opcode.Text)
+
+      await waitForClose(ws)
+
+    server = HttpServer.create(
+      address,
+      handle,
+      flags = {ReuseAddr})
+    server.start()
+
+    let client = await WebSocket.connect(
+      host = "127.0.0.1",
+      port = Port(8888),
+      path = "/ws",
+      protocols = @["proto"],
+      factories = @[hexFactory, base64Factory]
+    )
+
+    await client.send(testData)
+    let res = await client.recv()
+    check testData.toBytes() == res
+    await client.close()
+
+  test "base64 to hex ext flow":
+    let testData = "hello world"
+    proc handle(request: HttpRequest) {.async.} =
+      let server = WSServer.new(
+        protos = ["proto"],
+        factories = [hexFactory, base64Factory],
+      )
+      let ws = await server.handleRequest(request)
+      let recvData = await ws.recv()
+      await ws.send(recvData,
+        if ws.binary: Opcode.Binary else: Opcode.Text)
+
+      await waitForClose(ws)
+
+    server = HttpServer.create(
+      address,
+      handle,
+      flags = {ReuseAddr})
+    server.start()
+
+    let client = await WebSocket.connect(
+      host = "127.0.0.1",
+      port = Port(8888),
+      path = "/ws",
+      protocols = @["proto"],
+      factories = @[base64Factory, hexFactory]
+    )
+
+    await client.send(testData)
+    let res = await client.recv()
+    check testData.toBytes() == res
+    await client.close()
diff --git a/tests/testcommon.nim b/tests/testcommon.nim
index 93c05a4..dba53af 100644
--- a/tests/testcommon.nim
+++ b/tests/testcommon.nim
@@ -3,3 +3,4 @@
 import ./testframes
 import ./testutf8
 import ./testextutils
+import ./extensions/testexts