Convert MIT Scratch 3 (.sb3) projects into compilable C code.
scratch2c reads a Scratch project, builds an intermediate representation, infers C types for every variable, and emits clean C source for one of two targets: a standalone userspace program or a Linux kernel module.
A working alternative of the scratchnative program. If you've built something in Scratch and wondered how it will look like as C code, or you want to run your project as a real process on your laptop, or just learning about compilers, transpilers, and type systems and randomly stumbled upon this project, this is for you.
- A complete Scratch VM reimplementation
- A tool that supports graphics, sound, sprites, or anything visual
- Something that aims to run every Scratch project
# Clone and sync
git clone https://github.com/scratch2c/scratch2c.git
cd scratch2c
uv sync
# Transpile + compile + run (userspace)
make compile-userspace SB3=my_project.sb3
./build/my_project
# Transpile + build kernel module (needs linux-headers)
make kbuild SB3=my_project.sb3
sudo insmod build/my_project.ko
dmesg | tailThe Makefile handles copying scratch_runtime.h into the build directory, picking the right compiler flags, and invoking kbuild for kernel targets. You can also transpile without compiling:
make userspace SB3=my_project.sb3 # just emit build/my_project.c
make kernel SB3=my_project.sb3 # just emit build/my_project.c (kernel)Or call the CLI directly:
uv run scratch2c my_project.sb3 -o output.c --backend userspace
uv run scratch2c my_project.sb3 -o output.c --backend kernel| Category | Opcode | C output |
|---|---|---|
| Events | event_whenflagclicked |
main() / module_init() |
| Events | event_whenbroadcastreceived (init) |
module_init() |
| Events | event_whenbroadcastreceived (exit) |
module_exit() |
| Events | event_whenbroadcastreceived (other) |
named function |
| Control | control_repeat |
for loop |
| Control | control_forever |
while (1) |
| Control | control_repeat_until |
while (!cond) |
| Control | control_wait_until |
spin-wait loop |
| Control | control_if |
if |
| Control | control_if_else |
if / else |
| Control | control_stop |
return |
| Control | control_wait |
comment (no-op) |
| Data | data_setvariableto |
assignment |
| Data | data_changevariableby |
+= |
| Data | data_variable |
variable read |
| Looks | looks_say |
printf() / printk() |
| Looks | looks_sayforsecs |
printf() + comment |
| Operators | operator_add/subtract/multiply/divide/mod |
arithmetic |
| Operators | operator_lt/gt/equals |
comparison |
| Operators | operator_and/or/not |
boolean logic |
| Operators | operator_join |
scratch_join() |
| Operators | operator_length |
scratch_strlen() |
| Operators | operator_letter_of |
scratch_letter_of() |
| Operators | operator_contains |
scratch_contains() |
| Procedures | procedures_definition |
function definition |
| Procedures | procedures_call (with args) |
function call |
- No lists. Scratch lists would require dynamic arrays in C. Not implemented yet.
- Type inference is heuristic. If a variable holds both numbers and strings in the same program, the transpiler picks STRING as a safe fallback, but some edge cases may produce wrong types.
- No concurrency. Scratch runs multiple scripts in parallel via green threads. We emit them sequentially.
- Procedure arguments are always
long. Mixed-type procedure arguments need a tagged union, which we don't have yet. - No clone/sprite interaction. Multi-sprite programs are flattened.
uv sync # install everything
make test # run test suite
make compile-userspace SB3=projects/fibonacci.sb3 # transpile + gcc
make kbuild SB3=projects/fibonacci.sb3 # transpile + kbuild
make example-fib # dump both backends to stdout
make lint # mypy type-check
make clean # nuke build/MIT. See LICENSE.