diff --git a/API.md b/API.md
new file mode 100644
index 0000000..1c9927e
--- /dev/null
+++ b/API.md
@@ -0,0 +1,32 @@
+# API for X-Decor-libre
+
+X-Decor-libre is mostly self-contained but it allows for limited extension with
+a simple API. Not that extensibility is not the main goal of this mod.
+
+The function documentation can be found in the respective source code files
+under the header "--[[ API FUNCTIONS ]]".
+
+These are the features:
+
+## Add custom tool enchantments
+
+You can register tools to be able to be enchanted at the enchanting table.
+
+See `src/enchanting.lua` for details.
+
+## Add custom hammers
+
+You can add a custom hammer for repairing tools at the workbench,
+using custom stats.
+
+See `src/workbench.lua` for details.
+
+## EXPERIMENTAL: Add cut nodes
+
+You can register "cut" node variants of an existing node which can
+be created at the workbench.
+This will add thin stairs, half stairs, panels, microcubes, etc.
+
+THIS FEATURE IS EXPERIMENTAL!
+
+See `src/workbench.lua` for details.
diff --git a/README.md b/README.md
index b9348e1..fe2cfbd 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,10 @@ blocks with special features:
 * Pressure Plate: Step on it to activate doors next to it
 * Chessboard: Play Chess against a player or the computer (see `CHESS_README.md`)
 
+## For developers
+
+X-Decor-libre can be extended in a limited fashion. See `API.md` for details.
+
 ### X-Decor-libre vs X-Decor
 
 X-Decor is a popular mod in Luanti but it is (as the time of writing this text)
diff --git a/src/enchanting.lua b/src/enchanting.lua
index 19f4fcb..532c23b 100644
--- a/src/enchanting.lua
+++ b/src/enchanting.lua
@@ -398,7 +398,7 @@ minetest.register_craft({
 	}
 })
 
---[[ Enchanting API ]]
+--[[ API FUNCTIONS ]]
 
 --[[
 Register one or more enchantments for an already defined tool.
diff --git a/src/workbench.lua b/src/workbench.lua
index 0a17b7c..f85ce02 100644
--- a/src/workbench.lua
+++ b/src/workbench.lua
@@ -470,21 +470,6 @@ end
 
 -- Register hammer
 
-function xdecor.register_hammer(name, def)
-	minetest.register_tool(name, {
-		description = def.description,
-		_tt_help = S("Repairs tools at the work bench"),
-		inventory_image = def.image,
-		wield_image = def.image,
-		on_use = function() do
-			return end
-		end,
-		groups = def.groups,
-		_xdecor_hammer_repair = def.repair or DEFAULT_HAMMER_REPAIR,
-		_xdecor_hammer_repair_cost = def.repair_cost or DEFAULT_HAMMER_REPAIR_COST,
-	})
-end
-
 xdecor.register_hammer("xdecor:hammer", {
 	description = S("Hammer"),
 	image = "xdecor_hammer.png",
@@ -536,7 +521,48 @@ end
 workbench:register_special_cut("xdecor:cushion_block", { slab = "xdecor:cushion" })
 workbench:register_special_cut("xdecor:cabinet", { slab = "xdecor:cabinet_half" })
 
---[[ EXPERIMENTAL PUBLIC FUNCTION:
+--[[ API FUNCTIONS ]]
+
+--[[ Register a custom hammer (for repairing).
+A hammer repair items at the work bench. The workbench repeatedly
+checks if a hammer and a repairable tool are in the slots. The hammer
+will repair the tool in regular intervals. This is called a "step".
+In each step, the hammer reduces the wear of the repairable
+tool but increases its own wear, each by a fixed amount.
+
+This function allows you to register a custom hammer with custom
+name, item image and wear stats.
+
+Arguments:
+* name: Internal itemname
+* def: Definition table:
+    * description: Item `description`
+    * image: Inventory image and wield image
+    * groups: Item groups (MUST contain at least `repair_hammer = 1`)
+    * repair: How much item wear the hammer repairs per step
+    * repair_cost: How much item wear the hammer takes itself per step
+
+Note: Mind the implication of repair_cost! If repair_cost is lower than
+repair, this means practically infinite durability if you have two
+hammers that repair each other. If repair_cost is higher than repair,
+then hammers will break eventually.
+]]
+function xdecor.register_hammer(name, def)
+	minetest.register_tool(name, {
+		description = def.description,
+		_tt_help = S("Repairs tools at the work bench"),
+		inventory_image = def.image,
+		wield_image = def.image,
+		on_use = function() do
+			return end
+		end,
+		groups = def.groups,
+		_xdecor_hammer_repair = def.repair or DEFAULT_HAMMER_REPAIR,
+		_xdecor_hammer_repair_cost = def.repair_cost or DEFAULT_HAMMER_REPAIR_COST,
+	})
+end
+
+--[[ EXPERIMENTAL FUNCTION:
 Registers various 'cut' node variants for the node with the given nodename,
 which will be available in the workbench.
 This must only be called once per node. Calling it again is an error.