Assembly online compiler

What runs your code

Good to know

• Assembles 64-bit x86-64 Linux code with NASM 3 (nasm -f elf64).
• A program with a global main is linked with the C library, so it can call printf and scanf. One with _start is linked on its own and uses system calls.
• Use syscall with the 64-bit call numbers (1 is write, 60 is exit). 32-bit int 0x80 calls crash with exit code 139.

Run Assembly from your own code

Send the code and its input to the sync endpoint with an API key, and the output comes back in the response. The API docs cover the async endpoint with callbacks and every response field.

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "nasm-3",
    "code": "extern scanf\nextern printf\n\nsection .data\nfmt_in  db \"%63s\", 0\nfmt_out db \"Hello, %s!\", 10, 0\n\nsection .bss\nname    resb 64\n\nsection .text\nglobal main\nmain:\n    sub rsp, 8\n    lea rdi, [rel fmt_in]\n    lea rsi, [rel name]\n    xor eax, eax\n    call scanf\n    lea rdi, [rel fmt_out]\n    lea rsi, [rel name]\n    xor eax, eax\n    call printf\n    add rsp, 8\n    xor eax, eax\n    ret",
    "input": "Ada"
  }'

The response has output ("Hello, Ada!\n" here), error, exit_code, time and memory.

Put a runnable Assembly example on your site

The editor above is the embeddable widget. Add the script and a div with your widget key, and your readers can edit and run the code without an account:

<script src="https://onlinecompiler.io/widget.js"></script>

<div class="runcode" data-key="YOUR_WIDGET_KEY" data-lang="nasm-3">
  <script type="text/plain">
    extern scanf
    extern printf

    section .data
    fmt_in  db "%63s", 0
    fmt_out db "Hello, %s!", 10, 0

    section .bss
    name    resb 64

    section .text
    global main
    main:
        sub rsp, 8
        lea rdi, [rel fmt_in]
        lea rsi, [rel name]
        xor eax, eax
        call scanf
        lea rdi, [rel fmt_out]
        lea rsi, [rel name]
        xor eax, eax
        call printf
        add rsp, 8
        xor eax, eax
        ret
  </script>
</div>

On a platform that takes an iframe but not a script, such as many course sites, use the iframe embed. For Docusaurus, MkDocs, Sphinx and Mintlify, see runnable code examples in docs.

Other languages

Python, C, C++, Java, C#, F#, Go, Rust, PHP, Ruby, Haskell, TypeScript, JavaScript, SQL, Bash, Fortran, Visual Basic, Kotlin, R, Swift, COBOL, Perl, Julia, Pascal, Octave, Lua, OCaml, Common Lisp, Erlang, Elixir, Prolog, D, FreeBASIC, Dart, Clojure, Groovy, Scala, Zig, Nim, Crystal, Ada, PowerShell, Racket, Objective-C.

Frequently asked questions

Is this Assembly online compiler free?

Yes. Running Assembly on this page needs no account and shows no ads. To run Assembly from your own app or site, the API and the widget are free up to 100,000 runs a month, commercial use included.

Can my Assembly program read input?

Yes. Type it in the Input tab before you run, and the program reads it from standard input. The whole input is sent when you press Run, so a program can't ask for more while it runs.

Can I use Assembly libraries?

The C standard library, for programs that define <code>main</code>. There are no other libraries or include files, and programs have no network access.

How long can a program run?

Up to 30 seconds, with 512 MB of memory and 2 CPUs. A program still running at 30 seconds is stopped with exit code 124, and output over 64 KB per stream is cut.

Where does my code run?

On our servers, in a fresh gVisor sandbox with no network access that is deleted when the run ends. Each run is kept in execution history with its output; the security page says what is stored.