Standard library overview

Katnip’s standard library is not compiler magic — it is a set of .knip declaration files bundled into the compiler at build time. Each procedure is an empty body with an @opcode decorator naming the Scratch block it emits:

proc forward(@opcode = "motion_movesteps", steps: num) -> void {}

That means the standard library is readable, and you can see exactly which Scratch block any call becomes.

The namespaces

Namespace	Covers	Status
prelude	wait, stop, len, Key, true/false — no namespace prefix	🟢 mostly
events	hats, broadcasts	🟢
motion	movement, turning, position	🟢
looks	say/think, costumes, size, effects, layers	🟢
sensing	touching, mouse, keys, timer, ask/answer	🟢
pen	the pen extension	🟢
clone	clone lifecycle	🟢
list	list methods	🟡
dict	dict methods	🔴
str	string methods	🟡
math	constants and pow	🟡
console	log, warn, error, input	🔴

🟢 reaches real Scratch blocks · 🟡 partly · 🔴 type-checks but fails the build

Reading these pages

Each page lists signatures as declared. A ✅ means it compiles all the way to a .sb3 today; a ⛔ means it type-checks and then fails, with a note on what to write instead.

Two calling forms

Anything whose first parameter is named self is a method, callable either way:

scores.contains(4);           # method form     ✅
list.contains(scores, 4);     # namespace form  ⛔ fails at codegen

Both type-check, but only the method form builds today — the namespace form makes codegen look for a variable called list. Use the receiver form throughout.

Passing a menu value

Lots of stdlib procedures take an enum, because the Scratch block behind them has a dropdown. There are two ways to write one, and they compile to the same blocks:

motion.setRotationStyle(motion.RotationStyle.LEFT_RIGHT);   # the member
motion.setRotationStyle("left-right");                      # a literal that matches it

A literal that misses is an error listing the members, with a did-you-mean. Every page here gives the full member table so you can use either style.

Enums declared inside a namespace stay out of global scope, so reach them through the namespace. Prelude enums have no namespace and are bare names:

motion.Target.RANDOM      # ✅
Target.RANDOM             # error: 'Target' is not defined
Key.SPACE                 # ✅ prelude
stop(StopType.ALL);       # ✅ prelude

Caution

Only a literal coerces. A variable or a computed string is rejected — the slot is a Scratch menu, a shadow block, so a reporter there is almost always a mistake, and there is no cast to override it. See Known gaps.

The exception is the six menus that also list sprite, costume, and backdrop names — Target, TouchTarget, DistanceTarget, ObjectTarget, CloneTarget, Backdrop. Those parameters are typed Enum | str and take any string, computed or not.