What is Katnip?

Katnip is a typed programming language that compiles to Scratch. You write .knip files in a text editor, run the compiler, and get a .sb3 project file that opens in Scratch or TurboWarp and runs like any other project.

public score: num = 0;

proc award(points: num) -> void {
    score += points;
}

sprite Cat {
    events.onFlag() {
        pen.down();
        for (side, 4) {
            motion.forward(100);
            motion.turn(90);
            award(10);
        }
        pen.up();
        looks.say(f"Scored {score}!", 2);
    }
}

That compiles to a real Scratch project: a stage variable named score, a custom block named award, a green-flag script on the Cat sprite, and the pen extension enabled.

Why write Scratch as text?

Scratch’s block editor is wonderful for learning and painful at scale. Once a project grows past a few hundred blocks, the things text has always been good at start to matter:

You want	Blocks give you	Katnip gives you
Find every use of a variable	Scrolling	Ctrl+F
Reuse code between projects	Backpack, sort of	import
Catch a typo before running	Nothing	A type error, with line and column
Review a change	Screenshots	A diff
Copy a loop 20 times	20 drags	A for loop

Katnip is not a different runtime. There is no interpreter, no VM, no plugin to install in Scratch. The compiler emits ordinary Scratch blocks, so anything you build stays shareable, remixable, and readable by anyone who opens it in the editor.

What Katnip adds on top of Scratch

• Static types. num, str, bool, list<T>, dict<K, V>, tuples, unions, enums, and structs — all checked before a block is ever emitted.
• Real procedures. Return values (Scratch has none), overloads, default parameters, named arguments, and methods.
• Working recursion. The compiler analyses your call graph and picks a return strategy per procedure, so a recursive fib returns correct values instead of garbage.
• Dictionaries. Backed by two parallel Scratch lists, with d["key"] syntax.
• Operators Scratch lacks. <=, >=, ^, !&, !|, !^ are inlined at every use site as nested reporter blocks.
• Interpolated strings. f"{name} scored {score}" folds into a join chain.
• Modules. Split a project across files with import and public visibility.

What Katnip is not

• Not a Scratch decompiler. It goes one way: .knip → .sb3.
• Not a way to escape Scratch’s limits. There are no real function-local variables, no objects at runtime, no threads beyond Scratch’s own. Katnip is a nicer way to write Scratch, not a way to stop writing Scratch.
• Not finished. Several language features type-check but do not yet reach blocks — see Known gaps before you plan a project around one.

Where to go next

• Getting started — install the compiler and build your first .sb3 in about five minutes.
• Your first projects — three guided builds that take you from a square to a working game.
• The language — the reference, top to bottom.
• Known gaps — what does not work yet, and what to write instead.

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Katnip is Apache-2.0 licensed and developed at github.com/Katnip-org/Katnip.