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

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

Installation

[dependencies]
mcpls-core = "0.2"

Architecture

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

Module	Responsibility
`mcp/`	MCP server implementation with rmcp, 13 tool handlers
`bridge/`	Position encoding, document state, request translation
`lsp/`	JSON-RPC 2.0 client, process management, protocol types
`config/`	TOML parsing, server discovery, workspace configuration

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.