Writing an extension

An extension is a small Rust library compiled to WebAssembly with the crc-extension crate. Each command is a function:

use crc_extension::{Input, Output};

fn shout(input: Input) -> Output {
    Output::replace(input.text.to_uppercase())
}

crc_extension::commands! {
    "shout" => shout,
}

Input carries the text (the selection, or the whole document), whether it was a selection, and the language. An Output replaces the text, shows a message, or both.

Next to the code, a manifest.json names the extension, lists its commands and the capabilities it needs, and a README.md says what it does; crc shows both before anyone installs it.

Build it:

rustup target add wasm32-unknown-unknown
cargo build --release --target wasm32-unknown-unknown

Then in crc, Extensions > Extensions…, Install from Folder…, and pick the folder with the manifest, the README and the .wasm.

The full guide, the manifest reference and the rules for publishing to the official registry are in crc-extensions. Everything there is MIT or Apache 2.0, so your extension can use any licence.