LSP Setup for GitHub Copilot CLI

UTILITY SKILL — installs and configures Language Server Protocol servers for Copilot CLI.

When to Use

• When the user asks to enable code intelligence, go-to-definition, or hover information for Copilot CLI.
• When configuring a new development environment that lacks Language Server Protocol support.
• If Copilot CLI fails to provide contextual code completions due to a missing language server.

When Not to Use

• When configuring LSP servers for a full IDE like VS Code or Neovim (this is specifically for Copilot CLI).
• If the language does not have a widely supported or functioning Language Server Protocol implementation.
• For simple syntax highlighting tasks.

Common Pitfalls

• Missing Binary on PATH: Configuring the LSP JSON correctly but failing to ensure the installed binary is actually accessible in the system $PATH.
• Overwriting Configs: Using > to write the config file instead of safely merging, thereby destroying previously configured LSP servers for other languages.
• Forgetting to Restart: Assuming the new configuration takes effect immediately without instructing the user to exit and restart the Copilot CLI session.

Core Process

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.
4. Ask scope — use ask_user to ask whether the config should be user-level (~/.copilot/lsp-config.json) or repo-level (lsp.json at the repo root or .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; lsp.json or .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.

Core Principles

• 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.

Commands / Usage Patterns

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: lsp.json (repo root) or .github/lsp.json

The JSON structure:

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

• 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.

Diagnostics and Troubleshooting

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.

What to Avoid

• Do not overwrite existing servers inside the configuration.
• Do not assume a package manager is installed; verify first.
• Do not use for IDE/editor LSP configuration, only for Copilot CLI setups.

Limitations

• Some LSP servers might require additional dependencies (like Node.js, Python) which should be checked.

References

• copilot-cli/set-up-copilot-cli
• lsp-setup/SKILL.md
• Adding LSP servers for GitHub Copilot CLI
• Using LSP servers with GitHub Copilot CLI

Related Skills

• critical-thinking: You MUST load this skill when troubleshooting why an LSP isn't working or properly registering.