Introduction

WeaveFFI generates idiomatic bindings for 11 languages from one API definition, over a stable C ABI. Write the API as safe Rust annotated with #[weaveffi::module], or as a YAML or JSON IDL implemented by any library that can export C symbols (C, C++, Zig, and so on). WeaveFFI emits packages for C, C++, Swift, Kotlin, Node.js, WebAssembly, Python, .NET, Dart, Go, and Ruby that all call the same C functions.

The design in one page

One definition, two front doors. A Rust producer annotates ordinary modules; the #[weaveffi::module] macro emits the extern "C" thunks and embeds a description of the API in the compiled library, and the CLI reads that description back out to emit the bindings, so the bindings you ship describe exactly the library you compiled, #[cfg] included. A non-Rust producer writes an IDL instead and implements the C header WeaveFFI generates from it.

Identity drives every name. A library has one resolved identity: a package name, a C symbol prefix, and a native library base name. For a Rust producer all three come from the crate (kvstore gives kvstore_kv_Store_open, libkvstore.so, and an npm, PyPI, or NuGet package named kvstore). Nothing a generator emits is named after WeaveFFI, so any number of WeaveFFI-built libraries can live in one process.

A small, explicit C ABI. Revision 5 passes every value in one of a few families: direct scalars, optional scalars as a presence flag plus the value, numeric lists as typed arrays, UTF-8 strings and bytes as (ptr, len) runs, serialized value buffers for records, rich enums, and the remaining optionals, lists, and maps, and reference-counted objects, plus consumer-implemented callback vtables. Every fallible call reports through a {prefix}_error struct carrying a code, a length-delimited message, and the code’s fields. Async functions complete through a callback that fires exactly once, and cancellation is a first-class runtime code. Every consumer checks the ABI revision and each module’s contract table (a hash of every declaration’s signature, error code, and callback method) when it loads the library, so a stale binding fails loudly, naming the declaration that changed, instead of misreading memory, while a library that only added declarations, codes, or callback methods keeps loading.

Idiomatic generators. Each target maps the model onto its own idioms: objects become classes with deterministic disposal and a garbage-collector backstop, async functions become async/await, coroutines, promises, or tasks with native cancellation, iterators stay lazy, and error domains become typed exceptions or error values. The capability matrix summarizes all eleven: C, C++, Swift, Kotlin, Python, Node.js, and .NET are Tier 1, and Go, Ruby, Dart, and WebAssembly are Tier 2 (see Stability).

Standalone output. Generated packages are self-contained: helper code (the value-buffer codec, error types, object wrappers, loaders) is generated into each package, so consumers never install WeaveFFI. weaveffi package bundles prebuilt native libraries into publishable packages per ecosystem.

Where to next

• Getting Started: a Rust producer called from Python and C in a few minutes, plus the IDL path for a C implementation.
• The Rust Producer Macro: every supported signature and what the macro rejects.
• C ABI Contract: the normative description of the boundary.
• Comparison and FAQ: how WeaveFFI relates to UniFFI, Diplomat, cbindgen, and the single-language bridges.
• Stability and Versioning: what the version numbers promise, and how to migrate to schema 0.12 and ABI revision 5.