mcpls-core

The translation layer that makes AI understand code semantically.

mcpls-core bridges MCP and LSP protocols, transforming AI tool calls into language server requests and translating rich semantic responses back. It's the engine behind mcpls.

What it does

• Protocol translation — Converts MCP tool calls to LSP requests and back
• Position encoding — Handles MCP's 1-based positions ↔ LSP's 0-based coordinates
• LSP lifecycle — Manages language server processes (spawn, initialize, shutdown)
• Document tracking — Lazy-loads files, maintains synchronization state
• Configuration — Parses TOML configs, discovers LSP servers, manages language extension mappings
• Custom extension mapping — Configurable file extension-to-language ID mappings with sensible defaults
• Graceful degradation — Continues with available servers, even if some fail to initialize

[!NOTE] This is the library crate. For the CLI, see mcpls.

Installation

[dependencies]
mcpls-core = "0.3.1"

Architecture

flowchart LR
    subgraph mcpls-core
        M["mcp/"] -->|"tool calls"| B["bridge/"]
        B -->|"LSP requests"| L["lsp/"]
        C["config/"] -.->|"settings"| L
    end

Usage

use mcpls_core::config::Config;
use mcpls_core::mcp::McplsServer;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let config = Config::load()?;
    let server = McplsServer::new(config);
    server.run().await
}

Design principles

• Zero unsafe — Memory safety enforced at compile time
• Async-native — Built on Tokio for concurrent LSP management
• Error context — Rich error types with thiserror, never panics
• Resource limits — Bounded document tracking, configurable timeouts

License

Dual-licensed under Apache 2.0 or MIT.