If you've ever needed to know which register holds the third argument to a syscall on MIPS o32, you've lived one of two lives: the first involves grepping kernel headers for twenty minutes and hoping you picked the right version. The second involves syscall.sh, which has already done it for you across 27 architectures and every mainline kernel release from 3.3 to 7.3. The site is a reference tool, not a teaching tool — and that distinction matters. It doesn't explain what syscalls are or why you'd care. It assumes you already know and gives you the table you need: syscall numbers, argument registers, calling conventions, the instruction that traps into the kernel. Every architecture page shows the full history of when each syscall appeared and when (rarely) it was removed. There's a kernel-version selector and a JSON download for each arch. What makes this more than a pretty man page mirror is the sourcing. The data is generated by walking the actual kernel syscall tables and SYSCALLDEFINE macros of every scanned mainline release. This isn't scraped documentation — it's the numbers the kernel actually dispatches on. Short descriptions come from the Linux man pages project and liburing for iouring syscalls. When the upstream data changes, the site rebuilds from its own API. The API itself is clean and public: hit api.syscall.sh/v2/syscalls/x64/read and you get structured JSON back. Diffs between releases, per-architecture calling conventions, removed syscalls with the release that dropped them — it's all there. The architecture coverage is comprehensive in a way that reflects real-world embedded and systems work: not just x64 and arm64, but SuperH, PA-RISC, Hexagon, C-SKY, OpenRISC, m68k. Twenty-seven architectures total. The numbers themselves tell a quiet story about Linux's architectural sprawl. x86 (32-bit) carries 441 syscalls — the accumulated weight of decades of backwards compatibility. arm64, designed later with a cleaner slate, has 326. LoongArch, the newest addition (since 5.19), has 323 — essentially the modern baseline without legacy cruft. The delta between 323 and 441 is the cost of never breaking userspace. As a piece of developer infrastructure, syscall.sh sits in a category that rarely gets attention: the reference tool that saves thousands of people fifteen minutes each, built and maintained by someone who decided the kernel's own documentation wasn't accessible enough. It's not flashy. It doesn't need to be. The craft is in the completeness, the sourcing discipline, and the decision to cover everything rather than just the popular architectures.
