diff --git a/API.txt b/API.txt
index 180c6e1..625be84 100644
--- a/API.txt
+++ b/API.txt
@@ -61,3 +61,67 @@ The two values passed in are not guaranteed to be different, so plan accordingly
 
 Effect Types
 ============
+An effect type is a description of an effect, that can be applied later in an
+individual effect.
+
+Definition
+----------
+An effect type is defined with a table with the following properties (defaults
+in parens):
+
+  disp_name - Display name
+  dynamic - A bool for whether an effect of this type can have its values
+    changed (false)
+  tags - A set of tags ({})
+  monoids - The set of monoids this effect type affects
+  hidden - A boolean for whether it should be shown to the affected (false)
+  cancel_on_death - A boolean for whether this effect should be removed from the
+    player when they die.
+  values - A table mapping monoid names to associated values. These are the
+    values that will be combined in the monoid.
+  icon - A texture string (if nil, no icon is shown)
+
+
+Functions
+=========
+monoidal_effects.register_monoid("name", monoid_def)
+Registers a new effect monoid. name needs to be unique across all mods, so
+you should prepend your mod name, as in nodes/craftitems.
+
+monoidal_effects.register_type("name", type_def)
+Registers a new effect type. name needs to be unique.
+
+monoidal_effects.add_child_monoid("parent_name", "child_name"[, convert])
+Sets a monoid to be the child of another. When calculating the combined value
+for the parent monoid, values of the child monoids will also be mixed in, to
+the left of all "actual" values, in order of registration.
+
+monoidal_effects.apply_effect("effect_type", duration, "player_name"[, values])
+Applies a new effect of the specified type. duration should be a positive
+integer number of seconds or the string "perm". values is an optional table
+mapping monoid names to values, and is used with dynamic effect types to
+initialize the effect with custom values. Has no effect on static effect types.
+Returns an effect id.
+
+monoidal_effects.cancel_effect(effect_id)
+Cancels the given effect.
+
+monoidal_effects.cancel_monoid("monoid_name"[, "player_name"])
+Cancels all effects from a particular monoid on a player.
+
+monoidal_effects.cancel_effect_type("effect_type", "player_name")
+Cancels all effects from a player that are a certain effect_type. If player_name
+is nil, it cancels all matching effects from all players.
+
+monoidal_effects.cancel_tag("tag"[, "player_name"])
+Cancels all effects from a player with the given tag. If player_name is nil,
+it cancels all matching effects from all players.
+
+monoidal_effects.get_remaining_time(effect_id)
+Gets the remaining time of an effect, in seconds.
+
+monoidal_effects.get_player_effects("player_name")
+Gets a set of effects applied to the given player
+
+monoidal_effects.get_monoid_value("monoid_name", "player_name")
+Gets the current combined value for a monoid and player.