diff --git a/modules/watcher.py b/modules/watcher.py
new file mode 100755
index 0000000..7b54a26
--- /dev/null
+++ b/modules/watcher.py
@@ -0,0 +1,146 @@
+#!/usr/bin/env python3
+"""
+A thread watcher module for 4chan.
+"""
+import time
+import threading
+
+import requests
+
+from module import commands, example
+
+def setup(bot):
+	"""
+	Establishes the bot's dictionary of watched threads.
+	"""
+	bot.memory["watcher"] = {}
+
+
+def get_time():
+	"""
+	Returns the current time formatted in If-Modified-Since notation.
+	"""
+	return time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime())
+
+
+def get_num_posts(thread, name):
+	"""
+	Gets the number of OP posts from the thread JSON.
+	"""
+	num = 0
+	for post in thread["posts"]:
+		if post.get("name") == name:
+			num += 1
+	return num
+
+
+def get_last_post(thread, name):
+	"""
+	Gets the last post made by name.
+	"""
+	for post in reversed(thread["posts"]):
+		if post.get("name") == name:
+			return post.get("no")
+
+
+def get_api_url(url):
+	"""
+	Returns the API url for the provided thread url.
+	"""
+	return url.replace("boards.4chan", "a.4cdn") + ".json"
+
+
+def get_thread_url(api_url):
+	"""
+	Returns the normal thread url for the provided API url.
+	"""
+	return api_url.replace("a.4cdn", "boards.4chan").replace(".json", "")
+
+
+@commands("watch")
+@example(".watch https://boards.4chan.org/qst/thread/2")
+def watch(bot, trigger):
+	"""
+	A thread watcher for 4chan.
+	"""
+	url = trigger.group(3)
+	op_name = trigger.group(4)
+
+	if url in bot.memory["watcher"].keys():
+		return bot.say("Error: I'm already watching that thread.")
+
+	api_url = get_api_url(url)
+	res = requests.get(api_url, verify=True)
+	if res.status_code == 404:
+		return bot.say("404: thread not found")
+
+	thread = res.json()
+	last_post = get_last_post(thread, op_name)
+	time_since = get_time()
+
+	t = WatcherThread(bot, api_url, op_name, last_post, time_since)
+	t.start()
+	bot.memory["watcher"][url] = t
+	bot.say("[\x0304Watcher\x03] Watching thread: \x0307" + url)
+
+
+@commands("unwatch")
+@example(".unwatch https://boards.4chan.org/qst/thread/2")
+def unwatch(bot, trigger):
+	"""
+	Stops the thread watcher thread for that thread.
+	"""
+	url = trigger.group(2)
+	try:
+		bot.memory["watcher"][url].stop.set()
+		bot.memory["watcher"].pop(url)
+	except KeyError:
+		return bot.say("Error: I'm not watching that thread.")
+	return bot.say("[\x0304Watcher\x03] No longer watching: \x0307" + url)
+
+
+class WatcherThread(threading.Thread):
+	def __init__(self, bot, api_url, op_name, last_post, time_since):
+		threading.Thread.__init__(self)
+		self.stop = threading.Event()
+		self.period = 20
+
+		self.bot = bot
+		self.api_url = api_url
+		self.op_name = op_name
+		self.last_post = last_post
+		self.time_since = time_since
+
+
+	def run(self):
+		while not self.stop.is_set():
+			headers = {"If-Modified-Since": self.time_since}
+			res = requests.get(self.api_url, headers=headers, verify=True)
+			self.time_since = get_time()
+
+			if res.status_code == 404:
+				msg = "[\x0304Watcher\x03] Thread deleted: " \
+				+ f"\x0307{get_thread_url(self.api_url)}"
+				self.bot.say(msg)
+				self.stop.set()
+				continue
+
+			if res.status_code == 304:
+				self.stop.wait(self.period)
+				continue
+
+			thread = res.json()
+			if thread["posts"][0].get("closed"):
+				msg = "[\x0304Watcher\x03] Thread closed: " \
+				+ f"\x0307{get_thread_url(self.api_url)}"
+				self.bot.say(msg)
+				self.stop.set()
+				continue
+
+			new_last_post = get_last_post(thread, self.op_name)
+			if new_last_post > self.last_post:
+				self.last_post = new_last_post
+				msg = "[\x0304Watcher\x03] New post from \x0308" \
+				+ f"{self.op_name}\x03 in \x0307{get_thread_url(self.api_url)}"
+				self.bot.say(msg)
+			self.stop.wait(self.period)