mux-website-api

The compile/run API behind the Mux playground

A small Flask service that runs submitted Mux programs with the released mux binary and returns their output. Hosted on Fly.io as mux-lang-api (mux-lang-api.fly.dev), consumed by mux-website over HTTP.

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How it works

• POST /api/compile with { "code": "<mux source>" } -> { "output": "..." }
• GET /health for health checks
• The service shells out to mux run (rate-limited, time-limited) and returns stdout/stderr.

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Pinned compiler version

The Dockerfile installs a released mux binary (no Rust/LLVM build), pinned via ARG MUX_VERSION. The playground therefore runs a known, deliberately chosen compiler release. To upgrade the playground:

1. Ensure the target version is released in mux-compiler (the mux-linux-x86_64.tar.gz asset must exist).
2. Bump MUX_VERSION in the Dockerfile.
3. Deploy (below).

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Compiler-main canary (non-gating)

The release pin above is intentional: the playground must run a stable released compiler, not arbitrary main. To catch a compiler-main regression that would break this API's contract before the next release bump, a scheduled .github/workflows/canary-compiler-main.yml job builds mux from mux-compiler main and runs a smoke test (tests/canary_smoke.py) against it.

It runs only on a nightly schedule and manual dispatch (never on push or pull request), so it does not gate normal CI or deploys and is not a required check. It never changes the MUX_VERSION pin.

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Local development

pip install -r requirements.txt
# Needs a `mux` binary on PATH (see the mux-compiler install instructions).
MUX_BIN=mux gunicorn --bind 0.0.0.0:8080 server:app

Or build/run the production image (matches Fly):

docker build -t mux-website-api .
docker run --rm -p 8080:8080 mux-website-api

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Deployment

fly deploy

The slim image bundles clang-22 + the LLVM runtime libraries (the compiler shells out to clang and links LLVM at compile time) and sets MUX_RUNTIME_LIB so it never tries to build the runtime from source.

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Related repositories

Repo	What it is
mux-compiler	The language and compiler whose release this serves
mux-runtime	Runtime + standard library linked by compiled programs
mux-website	Docs site (mux-lang.dev) and playground UI
tree-sitter-mux	Tree-sitter grammar + highlight queries
mux-syntax-highlighting	TextMate grammar, VSCode extension, canonical syntax spec
mux-context	Cross-repo architecture, design rationale, glossary, releases

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License

MIT - Maintained by Derek Corniello