diff --git a/init.lua b/init.lua
index 8c29e1a..68d41e3 100644
--- a/init.lua
+++ b/init.lua
@@ -25,7 +25,7 @@
 
 ]]--
 
-filter = {}
+filter = { registered_on_violations = {} }
 local words = {}
 local muted = {}
 local violations = {}
@@ -57,6 +57,10 @@ function filter.import_file(filepath)
 	end
 end
 
+function filter.register_on_violation(func)
+	table.insert(filter.registered_on_violations, func)
+end
+
 function filter.check_message(name, message)
 	for _, w in ipairs(words) do
 		if string.find(message:lower(), "%f[%a]" .. w .. "%f[%A]") then
@@ -111,15 +115,23 @@ function filter.on_violation(name, message)
 
 	local resolution
 
-	if violations[name] == 1 and minetest.get_player_by_name(name) then
-		resolution = "warned"
-		filter.show_warning_formspec(name)
-	elseif violations[name] <= 3 then
-		resolution = "muted"
-		filter.mute(name, 1)
-	else
-		resolution = "kicked"
-		minetest.kick_player(name, "Please mind your language!")
+	for _, cb in pairs(filter.registered_on_violations) do
+		if cb(name, message, violations) then
+			resolution = "custom"
+		end
+	end
+
+	if not resolution then
+		if violations[name] == 1 and minetest.get_player_by_name(name) then
+			resolution = "warned"
+			filter.show_warning_formspec(name)
+		elseif violations[name] <= 3 then
+			resolution = "muted"
+			filter.mute(name, 1)
+		else
+			resolution = "kicked"
+			minetest.kick_player(name, "Please mind your language!")
+		end
 	end
 
 	minetest.log("action", "VIOLATION (" .. resolution .. "): <" .. name .. "> "..  message)
@@ -145,9 +157,9 @@ local function step()
 			violations[name] = nil
 		end
 	end
-	minetest.after(2*60, step)
+	minetest.after(10*60, step)
 end
-minetest.after(2*60, step)
+minetest.after(10*60, step)
 
 minetest.register_chatcommand("filter", {
 	params = "filter server",
diff --git a/readme.md b/readme.md
index 3b2c979..27293e2 100644
--- a/readme.md
+++ b/readme.md
@@ -1,5 +1,4 @@
-
-## filter mod
+# filter mod
 
 This mod adds a simple chat filter. There is no default word list,
 and adding words to the filter list is done through the `/filter`
@@ -14,7 +13,26 @@ muted for 1 minute. After that, their `shout` privilege is restored.
 If they leave, their `shout` privilege is still restored, but only after
 the time expires, not before.
 
-## Bugs
+## API
 
-- the `shout` priv is permanently lost if the server shuts down while
-a player is muted.
+### Callbacks
+
+* filter.register_on_violation(func(name, message, violations))
+	* Violations is the value of the player's violation counter - which is
+	  incremented on a violation, and halved every 10 minutes.
+	* Return true if you've handled the violation. No more callbacks will be
+	  executation, and the default behaviour (warning/mute/kick) on violation
+	  will be skipped.
+
+### Methods
+
+* filter.import_file(path)
+	* Input bad words from a file (`path`) where each line is a new word.
+* filter.check_message(name, message)
+	* Checks message for violation. Returns true if okay, false if bad.
+	  If it returns false, you should cancel the sending of the message and
+	  call filter.on_violation()
+* filter.on_violation(name, message)
+	* Increments violation count, runs callbacks, and punishes the players.
+* filter.mute(name, duration)
+* filter.show_warning_formspec(name)