lsp-setup

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:

{
  "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.
• 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.