---
name: lsp-setup
description: 'Enable code intelligence (go-to-definition, find-references, hover, type info) for any programming language by installing and configuring an LSP server for Copilot CLI. Detects the OS, installs the right server, and generates the JSON configuration (user-level or repo-level). Use when you need deeper code understanding and no LSP server is configured, or when the user asks to set up, install, or configure an LSP server.'
---

# LSP Setup for GitHub Copilot CLI

**UTILITY SKILL** — installs and configures Language Server Protocol servers for Copilot CLI.
USE FOR: "setup LSP", "install language server", "configure LSP for Java", "add TypeScript LSP", "enable code intelligence", "I need go-to-definition", "find references not working", "need better code understanding"
DO NOT USE FOR: general coding tasks, IDE/editor LSP configuration, non-Copilot-CLI setups

## Workflow

1. **Ask the language** — use `ask_user` to ask which programming language(s) the user wants LSP support for
2. **Detect the OS** — run `uname -s` (or check for Windows via `$env:OS` / `%OS%`) to determine macOS, Linux, or Windows
3. **Look up the LSP server** — read `references/lsp-servers.md` for known servers, install commands, and config snippets (for Java, also read `references/java-jdtls.md`)
4. **Ask scope** — use `ask_user` to ask whether the config should be user-level (`~/.copilot/lsp-config.json`) or repo-level (`.github/lsp.json`)
5. **Install the server** — run the appropriate install command for the detected OS
6. **Write the config** — merge the new server entry into the chosen config file (`~/.copilot/lsp-config.json` for user-level; `.github/lsp.json` for repo-level). Create the file if missing and preserve existing entries.
7. **Verify** — confirm the LSP binary is on `$PATH` and the config file is valid JSON

## Configuration Format

Copilot CLI reads LSP configuration from user-level or repo-level locations, and repo-level config takes precedence over user-level config:

- **User-level**: `~/.copilot/lsp-config.json`
- **Repo-level**: `.github/lsp.json` (a bare `lsp.json` at the repo root is not read: with Copilot CLI 1.0.95, `copilot lsp list` listed servers from `.github/lsp.json` but not from a root `lsp.json`)

The JSON structure:

```json
{
  "lspServers": {
    "<server-key>": {
      "command": "<binary>",
      "args": ["--stdio"],
      "fileExtensions": {
        ".<ext>": "<languageId>",
        ".<ext2>": "<languageId>"
      }
    }
  }
}
```

### Key rules

- `command` is the binary name (must be on `$PATH`) or an absolute path.
- `args` almost always includes `"--stdio"` to use standard I/O transport.
- `fileExtensions` maps each file extension (with leading dot) to a [Language ID](https://code.visualstudio.com/docs/languages/identifiers#_known-language-identifiers).
- Multiple servers can coexist in `lspServers`.
- When merging into an existing file, **never overwrite** other server entries — only add or update the target language key.

## Behavior

- Always use `ask_user` with `choices` when asking the user to pick a language or scope.
- If the language is not listed in `references/lsp-servers.md`, search the web for "<language> LSP server" and guide the user through manual configuration.
- If a package manager is not available (e.g. no Homebrew on macOS), suggest alternative install methods from the reference file.
- After installation, run `which <binary>` (or `where.exe` on Windows) to confirm the binary is accessible.
- Show the user the final config JSON before writing it.
- If the config file already exists, read it first and merge — do not clobber.

## Verification

After setup, tell the user:

1. Type `/exit` to quit Copilot CLI — this is **required** so the new LSP configuration is loaded on next launch
2. Re-launch `copilot` in a project with files of the configured language
3. Run `/lsp` to check the server status
4. Try code intelligence features like go-to-definition or hover

## Java

For Java semantic navigation, prefer the `lsp` tool (`goToDefinition`, `findReferences`, `hover`, `incomingCalls`) over grep/view once a server is configured. LSP is optional for Java and is not a prerequisite for build or runtime diagnostics. See `references/java-jdtls.md` for setup details and troubleshooting.