lspf

Build language capabilities in Rust for IDEs and AI agents. LSPF provides the Language Server Protocol runtime for both servers and clients.

Docs · crates.io · API · Examples · 简体中文

• Complete stable LSP 3.18 feature catalog, with capabilities generated from registrations.
• Framework-owned documents, workspace state, and position encoding negotiation.
• Cancellation, bounded concurrency, and partial results.
• stdio, TCP, WebSocket, WASM worker channels, and custom transports.
• Typed Client calls and supervised language-server processes for IDE and Agent hosts.

Try a working server: run the Markdown demo in Neovim, VS Code, or Zed. To build your own, start with the example below.

Minimal example

A hover handler that reads the document managed by LSPF. Save this as src/main.rs with the dependencies below, then run cargo build.

use std::sync::Arc;
use lspf::types::{Hover, HoverContents, HoverParams, MarkupContent, MarkupKind};
use lspf::{CancellationToken, LspError, Server, ServerContext};

async fn hover(
    _state: Arc<()>,
    ctx: ServerContext,
    params: HoverParams,
    _cancel: CancellationToken,
) -> Result<Option<Hover>, LspError> {
    let uri = params.text_document_position_params.text_document.uri;
    Ok(ctx.documents().get(&uri).map(|doc| Hover {
        contents: HoverContents::MarkupContent(MarkupContent {
            kind: MarkupKind::PlainText,
            value: format!("{} words", doc.text(None).split_whitespace().count()),
        }),
        range: None,
    }))
}

#[tokio::main]
async fn main() -> lspf::Result<()> {
    let server = Server::builder(())
        .feature(lspf::features::hover(), hover)
        .build()
        .expect("valid registrations");
    let outcome = lspf::stdio(server).serve().await?;
    std::process::exit(outcome.code());
}

Point your editor's LSP command at target/debug/my-language-server. Opening a document and hovering returns its word count; LSPF handles initialization, synchronization, and shutdown. The server tutorial adds diagnostics and commands.

See it work in 30 seconds

lspf-markdown checks local Markdown links, shows their resolved targets on hover, and jumps to target headings. This is a real Neovim session using the in-tree server over stdio. Replay or record the demo.

git clone https://github.com/meymchen/lspf.git
cd lspf
cargo install --path crates/lspf-markdown --locked
nvim --clean -u editor-validation/neovim/init.lua editor-validation/fixture/readme.md

Requires Rust 1.98+, Neovim 0.11+, and Cargo's bin directory on PATH. Compilation happens before the 30-second demo. Put the cursor inside missing.md to inspect the diagnostic, then inside guide.md for hover and definition. The Neovim quick start includes explicit commands and a small configuration you can adapt to your own server.

Why LSPF?

Let the framework own the protocol runtime

Register the language operations your application needs with .feature(lspf::features::hover(), hover) or .feature(lspf::features::completion(options), complete), as in the expanded example below.

LSPF owns initialize, shutdown and exit, JSON-RPC dispatch, document synchronization, workspace state, and UTF-8/UTF-16/UTF-32 position negotiation. It also provides cancellation tokens, bounded concurrent dispatch, request-scoped partial results, typed server-to-client requests, and transport adapters. Handlers access this state through ServerContext.

Documents are updated before document hooks run. Capabilities come from the same registrations that dispatch requests; conflicting registrations fail at build time. Your application owns parsing, indexing, analysis, and the policy for using those results.

Extend language capabilities for IDEs and agents

A definition handler can power an editor's navigation action or an agent's source lookup through LSP. Diagnostics can appear in an editor or feed an automated edit-and-check loop. Implement the operation once in a server and expose it to hosts that speak the protocol.

LSPF also supplies the Client endpoint. An IDE or Agent host can launch a language server as a supervised stdio child, receive diagnostics, and issue typed requests through ServerHandle:

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let child = lspf::Client::builder(lspf::types::ClientCapabilities::default())
        .spawn(tokio::process::Command::new("lspf-markdown"))
        .await?;
    let _server = child.server();
    // Send document notifications and typed requests through `_server`.
    // Keep `child` alive while the host uses the connection.
    let output = child.shutdown().await?;
    assert!(output.status().success());
    Ok(())
}

The Client tutorial is a runnable host that opens a document, receives diagnostics, requests hover, and executes a command. Use it as the starting point for an Agent's code tools. The host owns document contents and versions, tool schemas, model integration, and decisions about applying edits. LSPF supplies the typed protocol connection and process lifecycle.

Keep language logic independent of the host

Use stdio for a local editor or Agent process, TCP or WebSocket for a native connection, or worker channels in a WASM host. The transport examples reuse shared handlers. Custom Transport implementations can connect an embedded host or a test peer to the same protocol engine.

Quick start

Create a binary crate:

cargo new my-language-server
cd my-language-server

Add the dependencies under Install, then paste the minimal example into src/main.rs and run cargo build. Launch the resulting executable through an LSP client; it waits for protocol messages on stdin. Write logs to stderr because stdout carries the protocol.

The expanded example below adds completion, a workspace command, disk access, and tracing.

use std::sync::Arc;

use lspf::types::{
    CompletionItem, CompletionItemKind, CompletionOptions, CompletionParams, CompletionResponse,
    Hover, HoverContents, HoverParams, MarkupContent, MarkupKind,
};
use lspf::{CancellationToken, ServerContext, LspError, OsFileProvider, Server};

/// Only your own application state — the framework owns the documents, the
/// workspace, and the client, and hands them to handlers through `ServerContext`.
struct State;

/// A standard typed feature. The `features::hover()` descriptor fixes the
/// wire method, this handler's parameter and result types, and the
/// `hoverProvider` capability the server will advertise — all at once.
async fn hover(
    _state: Arc<State>,
    ctx: ServerContext,
    params: HoverParams,
    _ct: CancellationToken,
) -> Result<Option<Hover>, LspError> {
    let uri = params.text_document_position_params.text_document.uri;
    let Some(document) = ctx.documents().get(&uri) else {
        return Ok(None);
    };
    Ok(Some(Hover {
        contents: HoverContents::MarkupContent(MarkupContent {
            kind: MarkupKind::PlainText,
            value: format!("{} words", document.text(None).split_whitespace().count()),
        }),
        range: None,
    }))
}

/// A second typed feature; the options supplied here are exactly what the
/// generated `completionProvider` advertises.
async fn complete(
    _state: Arc<State>,
    _ctx: ServerContext,
    _params: CompletionParams,
    _ct: CancellationToken,
) -> Result<Option<CompletionResponse>, LspError> {
    Ok(Some(CompletionResponse::CompletionItemList(vec![CompletionItem {
        label: "hello".into(),
        kind: Some(CompletionItemKind::Text),
        ..CompletionItem::default()
    }])))
}

/// A typed Command, dispatched by name beneath `workspace/executeCommand`.
/// Registering it adds the name to the generated `executeCommandProvider`,
/// in registration order.
async fn roots(
    _state: Arc<State>,
    ctx: ServerContext,
    _args: Vec<String>,
    _ct: CancellationToken,
) -> Result<Vec<(String, String)>, LspError> {
    Ok(ctx
        .workspace()
        .roots()
        .into_iter()
        .map(|folder| (folder.uri.as_str().to_string(), folder.name))
        .collect())
}

#[tokio::main]
async fn main() -> lspf::Result<()> {
    // Logs go to stderr: stdout carries the LSP wire protocol and nothing else.
    tracing_subscriber::fmt()
        .with_writer(std::io::stderr)
        .with_ansi(false)
        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
        .init();

    let server = Server::builder(State)
        // Unopened `file:` URIs resolve from disk through this provider.
        .file_provider(OsFileProvider::new())
        .feature(lspf::features::hover(), hover)
        .feature(
            lspf::features::completion(CompletionOptions {
                trigger_characters: Some(vec![".".to_string()]),
                ..CompletionOptions::default()
            }),
            complete,
        )
        .command("hello.roots", roots)
        .build()
        .expect("the static registrations are valid");
    // Serving reports how the connection ended; the binary decides what that
    // means for the process.
    let outcome = lspf::stdio(server).serve().await?;
    std::process::exit(outcome.code());
}

No handwritten ServerCapabilities and no framework change are involved: the capabilities come from the registrations themselves. For a ready-to-copy server and editor extension, start from lspf-vscode-extension-template or lspf-intellij-platform-plugin-template. The framework's public feature, workspace, client, and stdio seams are covered by the crates/lspf integration tests and the in-tree lspf-markdown reference server. The feature registration and workspace state guides walk through each piece. To choose a Transport adapter, enable only its Cargo dependencies, or implement another message-framed channel, see Choosing a Transport, then continue to stdio and custom transports when the host owns a child process or a custom message-framed channel. To build the same server one step at a time, start with the Server tutorial, then use the Client tutorial to drive it as a supervised stdio child. For custom Client Transports and reverse handlers, follow the Client adoption guide. Runnable servers for individual LSP features are indexed in crates/lspf/examples/README.md.

Install

[dependencies]
lspf = "1.0.0"
tokio = { version = "1", features = ["macros", "rt-multi-thread", "process"] }
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }

The crate requires Rust 1.98 or newer. The minimal example needs only lspf and tokio; the expanded example also uses the tracing dependencies. Both examples use the default stdio feature; select a different feature set for another Transport.

List every crate your application names directly. Tokio's process feature is included for the Client example. The expanded server uses tracing-subscriber to configure framework logs on stderr.

Editor quick starts

All three guides use the same lspf-markdown executable and fixture:

• Neovim: built-in LSP, no plugin required.
• VS Code: the bundled language-client extension.
• Zed: the bundled development extension.

For a new server bundled into an editor extension, use lspf-vscode-extension-template or, for a JetBrains IDE 2026.2 or later, lspf-intellij-platform-plugin-template. Each template's README covers generation, renaming, and the build and debug commands. For individual protocol operations, browse the runnable examples. The editor validation journeys record the shared protocol checks and editor observations.

Concepts

The vocabulary below is taken from CONTEXT.md; the project deliberately standardizes on these terms in the public API and the docs.

Architecture

The project documentation covers features, transports, testing, operations, and both endpoint tutorials. The repository keeps the material needed to maintain those contracts:

• CONTEXT.md defines the domain language.
• docs/adr/ records architecture decisions.
• docs/public-interface.md freezes the 1.0 public interface.
• SECURITY.md defines supported platforms, compatibility, and vulnerability reporting.

See CONTRIBUTING.md before changing these boundaries.

Current scope

See the package changelog for release history.

The support contract is authoritative for maintained Rust versions, hosts, targets, and Cargo feature combinations. The operations guide records the deployment and application responsibilities that lspf deliberately leaves to its host.

Available today:

• stdio, single-client TCP, WebSocket, and WASM worker-channel adapters, plus the public custom-transport interface.
• A typed Client endpoint over custom Transport and supervised stdio child, with reverse handlers, bounded resources, deadlines, and lifecycle control.
• The built Server: typed requests, notifications, commands, the sealed feature catalog covering the complete stable LSP 3.18 surface, user Layers, and the one configure_initialize transaction. The 3.18 additions are textDocument/inlineCompletion, workspace/textDocumentContent, and textDocument/rangesFormatting.
• Lifecycle hooks through shutdown and exit, incremental or full text-document synchronization, and post-mutation document hooks.
• Notebook document synchronization across notebookDocument/didOpen, didChange, didSave, and didClose, with notebook structure read through ctx.notebooks() and cell text through the same ctx.documents() view as any other document.
• The multi-root Workspace, latest configuration settings, and FileProvider-backed unopened-file lookup.
• Typed server-to-client notifications and correlated requests through ClientHandle, including all seven stable workspace refresh requests.
• Partial-result reporting: a handler for a request that carries a partialResultToken reports typed chunks through ctx.partial_results() under the connection's outbound budget.
• Concurrent dispatch, bounded concurrency, request cancellation, and tracing spans.
• Rope-backed documents with UTF-8/UTF-32/UTF-16 position negotiation.

Contributing

Read CONTRIBUTING.md for setup, project context, tests, documentation rules, debugging, and pull request conventions. Issues live on the GitHub tracker.

License

Dual-licensed under either of

• Apache License, Version 2.0
• MIT License

at your option.