diff --git a/README.md b/README.md
index fef4f88..57e097e 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,8 @@ Rules have five fields. Only `matches` and `template` are required.
 * `rooms` - The list of rooms where the rule should apply.
             If empty, the rule will apply to all rooms the bot is in.
 * `matches` - The regex or list of regexes to match.
+* `probability` - The probability the rule will be executed expressed as a float
+                  between 0 and 1.0. Defaults to 1.0.
 * `template` - The name of the template to use.
 * `variables` - A key-value map of variables to extend or override template variables.
                 Like with template variables, the values are parsed as Jinja2 templates.
diff --git a/reactbot/config.py b/reactbot/config.py
index efbf9ae..77cbb45 100644
--- a/reactbot/config.py
+++ b/reactbot/config.py
@@ -59,6 +59,7 @@ class Config(BaseProxyConfig):
                         not_rooms=set(rule.get("not_rooms", [])),
                         matches=self._compile_all(rule["matches"]),
                         not_matches=self._compile_all(rule.get("not_matches", [])),
+                        probability=rule.get("probability", 1.0),
                         type=EventType.find(rule["type"]) if "type" in rule else None,
                         template=self.templates[rule["template"]],
                         variables=self._parse_variables(rule))
diff --git a/reactbot/rule.py b/reactbot/rule.py
index b97b350..4e338f4 100644
--- a/reactbot/rule.py
+++ b/reactbot/rule.py
@@ -18,6 +18,8 @@ from typing import Optional, Match, Dict, List, Set, Union, Pattern, Any
 from attr import dataclass
 from jinja2 import Template as JinjaTemplate
 
+from random import random
+
 from mautrix.types import RoomID, EventType
 
 from maubot import MessageEvent
@@ -34,6 +36,7 @@ class Rule:
     not_rooms: Set[RoomID]
     matches: List[RPattern]
     not_matches: List[RPattern]
+    probability: float
     template: Template
     type: Optional[EventType]
     variables: Dict[str, Any]
@@ -49,6 +52,8 @@ class Rule:
             return None
         elif evt.room_id in self.not_rooms:
             return None
+        elif self.probability < random():
+            return None
         for pattern in self.matches:
             match = pattern.search(evt.content.body)
             if match: