Ruby — LSP setup

• Builtin server: ruby-lsp — rubocop --lsp
• Extensions: .rb .rake .gemspec .ru
• Install hint: gem install ruby-lsp

Note: the builtin id is ruby-lsp, but the executable actually invoked is rubocop (rubocop --lsp). RuboCop must be installed: gem install rubocop.

Install

• macOS: gem install rubocop (and gem install ruby-lsp for the install hint's gem)
• Linux: gem install rubocop
• Windows: gem install rubocop

In a Bundler project, prefer adding rubocop to the Gemfile and running via bundle exec.

Confirm it resolves (check rubocop, since that is what runs):

command -v rubocop

Configure

Builtin — usually NO config needed (auto-resolved by extension). Configure only to set priority, init options, override extensions, or disable. Same JSON shape in .codex/lsp-client.json (Codex) AND .opencode/lsp.json (OpenCode/omo):

{ "lsp": { "ruby-lsp": { "priority": 100 } } }

For builtin ids in a PROJECT config, command is supplied automatically — only set priority/initialization/extensions/disabled/env. A fully custom (non-builtin) server with its own command must go in the USER config (~/.codex/lsp-client.json).

Initialization options (only if commonly needed)

None commonly required. Behavior is driven by your .rubocop.yml; the server surfaces RuboCop diagnostics, formatting, and code actions over LSP.

Alternatives

• ruby-lsp gem server (not builtin) — the standalone Shopify Ruby LSP binary (ruby-lsp executable), richer navigation than RuboCop alone. Configure as a custom server with command: ["ruby-lsp"] in the USER config.
• solargraph (not builtin) — older completion/type server; install with gem install solargraph, custom command: ["solargraph", "stdio"].

Troubleshooting

• PATH: rubocop on PATH (that is the invoked binary, not ruby-lsp); reopen shell after install.
• rubocop not found: the builtin fails even if the ruby-lsp gem is installed — install RuboCop with gem install rubocop.
• Bundler mismatch: if the project pins RuboCop in its Gemfile, run inside the bundle so versions match.
• No diagnostics: check .rubocop.yml is valid and not disabling everything.

Verify

bun ../../scripts/verify-lsp.ts path/to/file.rb