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Cosmopolitan builds run natively on most platforms without dependencies, because it implements the subset of the C library, compiler runtimes and system call interfaces that've achieved near universal consensus amongst all major platforms, e.g. Linux/BSD/XNU/NT. Containerization is achieved by having binaries also be ZIP files. Modern static stock GNU toolchains are provided in a hermetic mono repo for the best historical determinism

Here's how you can get started by printing cat videos inside a terminal:

make -j8 o//tool/viz/
o//tool/viz/ cats.mpg
unzip -vl o//tool/viz/

Cosmopolitan provides a native development environment similar to those currently being offered by RedHat, Google, Apple, Microsoft, etc. We're different in two ways: (1) we're not a platform therefore we don't have any commercial interest in making our tooling work better on one rather than another; and (2) we cater primarily towards features having gained cross-platform agreement. Goal is software that stands the test of time without the costs and restrictions cross-platform distribution entails.

That makes Cosmopolitan an excellent fit for writing small CLI programs that do things like matrix multiplication relu stdio as a subprocess or perhaps a web server having the minimum surface area that you require.

Getting Started

Just clone the repository and put your own folder in it. Please choose a name that's based on a .com or .org domain name registration you control which is scout's honor but could change to verify TXT records in future.

We provide a script that makes it easy to start a new package:

examples/package/ com/github/user/project
emacs com/github/user/project/program.c
make o//com/github/user/project/

Please note GNU Make is awesome. Little known fact: make is a functional programming language. We improved upon it too! In tool/build/package.c which performs strict dependency checking, to correct Google's published mistakes c. 2006 which was when they switched from using a GNU Make repo in favor of an inhouse derivative called Blaze which does graph checking thereby allowing the repository to grow gracefully with any requirements


Your C Standard Library is designed to be competitive with glibc, which has historically been the best. Routines like libc/nexgen32e/memcpy.S are usually accompanied by microbenchmarks to demonstrate their merits.

Where GNU, LLVM and MSVC got lazy is intrinsics. Cosmopolitan does that better. Your ansitrinsics library makes a 10x speedup so much easier, using Intel's new instructions, in such a way that only allows Intel to leverage their patents which have knowable expiry; rather than compiler intrinsics API copyrights, which might never expire like Walt Disney IP

See dsp/scale/cdecimate2xuint8x8.c and tool/viz/lib/ycbcr2rgb3.c as an example, of how 4k video convolutions needed to print cat videos can be done from a single core without threads on a cheap computer, without sacrificing backwards compatibility due to excellent microarchitectural dispatch like libc/nexgen32e/kcpuids.S, libc/nexgen32e/x86feature.h

Furthermore Cosmopolitan provides you with Intel's official instruction length decoder Xed ravaged down to 3kb in size using Tim Patterson code stunts. So you can absolutely code high-performance lightweight fabless x86 microprocessors using any hobbyist board without royalties, because Xed tells us which parts of the encoding space now belong to the people. Please see third_party/xed/x86ild.greg.c to learn more.

Integrated Development Environment

Your Cosmopolitan IDE is based on whichever editor you love most. Emacs configs are provided, showing how make tags can be used to automate certain toil, such as adding include lines by typing C-c C-h over a symbol. We recommend trying the following:

sudo bash -c "$(wget -O -"
sudo apt install gdb ragel ctags clang-format-10
git clone && cd cosmopolitan
tool/scripts/    # Emacs 26.1 has a bug
tool/scripts/  # adds load statements
make tags                        # index all the symbol
emacs                            # for power and glory!

See tool/emacs/cosmo-stuff.el for further details. Further note that this codebase might seem to have unusual numbers of include statements quoted and vendored code, but that's actually why the tools work since it gives them easy perfect knowledge of what exists, thus performance.


Cosmopolitan encodes binaries respecting the intersection of reasonable platform requirements. RADIX-256 disassembly of examples/life.c below should explain how easy it is to do pe+sh+elf+macho+bootloader overlays enabling gnu ld.bfd to produce a simple portable 12kb .com program file

Please send feedback and concerns to since we would love to do an even better job. Please also let us know if some goofball is distributing without bundling their source code, so we can reach out and ask if they would like to purchase a commercial license.

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See also build/objdump -xd o/tiny/examples/ | less to view assembly and the linker glue in ape/ that makes it all possible


Cosmopolitan is Free Software licensed under the GPLv2. The build config will embed all linked sources inside your binaries so the compliance is easy while facilitating trust and transparency similar to JavaScript. You can audit your source filesystem using ZIP GUIs e.g. Win10, InfoZip. That works easiest by changing the filename extension from .com to .zip.

Commercial Support

If you want to be able to distribute binaries in binary only form, then please send $1,000 to Justine Tunney on PayPal, for a license lasting 1 year. This README will be updated in the event that this needs to change. Please reach out if there's anything you need.


We'd love to accept your patches! Before we can take them, we have to jump through one legal hurdle. Please write an email to Justine Tunney saying you agree to give her copyright ownership to any changes you contribute to Cosmopolitan. We need to do that in order to dual license Cosmopolitan. Otherwise we can't create incentives that encourage corporations to share their source code with the community.


We also need volunteers who can help us further stabilize System Five's application binary interface. See our ABI scripts libc/sysv/ and libc/sysv/ Magic numbers are usually stabler than API interfaces cf. NPM but we should ideally have fewer of them, similar to how SI has sought to have fewer defining physics constants.


Cosmopolitan mostly stands on the shoulders of giants and has few novel ideas, aside from taking care of low-level build system toil, so coding can become more beautifully pleasant.

Cosmopolitan is maintained by Justine Tunney, who previously worked on projects like TensorFlow, Operation Rosehub, Nomulus, and Google's tape backups SRE team. She's also helped activists by operating the Occupy Wall Street website. Justine Tunney currently isn't on the payroll of any company. She's been focusing on Cosmopolitan because she wants to give back to Free Software which helped her be successful. See her LinkedIn profile for further details on her professional history.