dtolnay/watt

Health v2 · maintenance only

Adoption not part of the score

1523 stars · 31 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

Watt is a Rust runtime for executing procedural macros that have been compiled ahead-of-time to WebAssembly. It lets downstream users run macros in a small, dependency-free Wasm interpreter instead of compiling the macro and its dependencies from source.

Use cases

• speed up compilation of crates that depend on procedural macros
• run proc macros in a sandboxed, 100% safe-code environment
• make macro expansion deterministic for build systems
• distribute proc macros as precompiled Wasm bytecode
• reduce dependency compile times for syn/quote-heavy macro crates

When to choose

• your proc macro and its dependencies are slow to compile and many crates depend on it
• you want strong isolation guarantees so macros can only transform tokens
• you need deterministic macro behavior visible to the build system

When to avoid

• you need proc macro APIs or dependencies not supported by the Wasm runtime
• your project is small and macro compile time is not a bottleneck
• you need tight integration with the latest unstable proc_macro features

Facets

library · maturity active

compiler wasm developer-tools developer-tools compilers programming-languages rust wasm cross-platform proc-macro webassembly-runtime build-time rust-macros sandboxing

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