#language-server #lsp #tower


A lightweight framework for implementing LSP servers

7 releases (4 breaking)

new 0.6.2 Feb 25, 2021
0.6.1 Feb 8, 2021
0.6.0 Jan 29, 2021
0.5.0 Jan 28, 2021
0.1.0 Dec 14, 2020

#34 in Asynchronous

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10,510 downloads per month
Used in deno

Apache-2.0 WITH LLVM-exception

1.5K SLoC


A Language Server Protocol implementation for Rust based on Tower

Tower is a simple and composable framework for implementing asynchronous services in Rust. Central to Tower is the Service trait, which provides the necessary abstractions for defining request/response clients and servers. Examples of protocols implemented using the Service trait include hyper for HTTP and tonic for gRPC.

This library (lspower) provides a simple implementation of the Language Server Protocol (LSP) that makes it easy to write your own language server. It consists of three parts:

  • The LanguageServer trait which defines the behavior of your language server.
  • The asynchronous LspService delegate which wraps your language server implementation and defines the behavior of the protocol.
  • A Server which spawns the LspService and processes requests and responses over stdio or TCP.


use lspower::jsonrpc::Result;
use lspower::lsp::*;
use lspower::{Client, LanguageServer, LspService, Server};

struct Backend {
    client: Client,

impl LanguageServer for Backend {
    async fn initialize(&self, _: InitializeParams) -> Result<InitializeResult> {

    async fn initialized(&self, _: InitializedParams) {
            .log_message(MessageType::Info, "server initialized!")

    async fn shutdown(&self) -> Result<()> {

async fn main() {
    let stdin = tokio::io::stdin();
    let stdout = tokio::io::stdout();

    let (service, messages) = LspService::new(|client| Backend { client });
    Server::new(stdin, stdout)

Differences with tower-lsp

lspower is a fork of the tower-lsp crate.

The main differences between these crates are the following:

  • lspower is currently maintained while tower-lsp development seems to have stopped
  • lspower has had a number of small refactorings and bug-fixes since the fork
  • lspower does not require tokio and works with async-std, smol, tokio, and the futures executor
  • lspower works for WASM targets (resolving issue: tower-lsp#187)

Using lspower with runtimes other than tokio

By default, lspower is configured for use with tokio.

Using lspower with other runtimes requires disabling default-features and enabling the runtime-agnostic feature:

version = "*"
default-features = false
features = ["runtime-agnostic"]


lspower is free and open source software distributed under the terms of either the MIT or the Apache 2.0 license, at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


lspower is a fork of the tower-lsp crate.


~171K SLoC