WASM Plugins¶

Language Check supports WebAssembly plugins loaded via Extism.

Configuration¶

engines:
  wasm_plugins:
    - name: custom-checker
      path: .languagecheck/plugins/checker.wasm
      extensions: [md, html]
    - name: style-linter
      path: /opt/plugins/style.wasm

Plugin Interface¶

Plugins must export a check function with the following contract:

Input¶

A JSON string passed as the function argument:

{
  "text": "The document text to check.",
  "language_id": "markdown"
}

Output¶

A JSON string returned as the function result — an array of diagnostics:

[
  {
    "start_byte": 0,
    "end_byte": 3,
    "message": "Capitalize the first word.",
    "suggestions": ["The"],
    "rule_id": "style.capitalization",
    "severity": 2,
    "confidence": 0.9
  }
]

The diagnostic schema is identical to external providers.

Plugin Discovery¶

Plugins can also be auto-discovered from a directory:

.languagecheck/
  plugins/
    spell-checker.wasm
    style-linter.wasm

Any .wasm file in the plugins directory is loaded automatically, with the filename (minus extension) used as the plugin name.

Building Plugins¶

For a step-by-step tutorial, see the WASM Plugin Guide. A complete reference implementation is available in plugins/wordiness-check/.

Plugins can be built with the Extism PDK in any language that compiles to WebAssembly:

Rust: extism-pdk crate
Go: extism-pdk-go
JavaScript: @nicolo-ribaudo/extism-pdk
AssemblyScript, Zig, C/C++, Haskell

Example (Rust)¶

use extism_pdk::*;
use serde::{Deserialize, Serialize};

#[derive(Deserialize)]
struct CheckRequest {
    text: String,
    language_id: String,
}

#[derive(Serialize)]
struct Diagnostic {
    start_byte: u32,
    end_byte: u32,
    message: String,
    suggestions: Vec<String>,
    rule_id: String,
    severity: i32,
    confidence: f32,
}

#[plugin_fn]
pub fn check(input: String) -> FnResult<String> {
    let req: CheckRequest = serde_json::from_str(&input)?;
    let mut diagnostics = Vec::new();

    // Your checking logic here...

    Ok(serde_json::to_string(&diagnostics)?)
}

Error Handling¶

Invalid WASM modules are logged and skipped during initialization.
Runtime errors during check() calls return empty diagnostics.
WASM plugins are skipped in High Performance Mode.

Rule ID Namespacing¶

Rule IDs from WASM plugins are prefixed with wasm.<plugin-name>. for disambiguation.