Language Servers

In this chapter you set up the language servers for the languages you use and learn what to expect from each. mcpls works with any LSP 3.17 server, and six are built in.

Prerequisites

• mcpls installed and a configuration file if you go beyond the defaults.

Built-in servers

These start with no configuration when their project markers are present:

Confirm each server runs by itself before you debug mcpls, for example rust-analyzer --version or gopls version.

TypeScript needs a JavaScript TypeScript

typescript-language-server drives a JavaScript tsserver, and TypeScript 7 ships none. Install typescript@6 next to it, as above. If you want the TypeScript 7 native server instead, see TypeScript: tsserver Pinning and TypeScript 7.

Alternatives and extra servers

Replace or add servers with [[lsp_servers]] entries. Each example below is a complete entry.

Python with ty instead of pyright:

[[lsp_servers]]
language_id = "python"
command = "ty"
args = ["server"]
file_patterns = ["**/*.py", "**/*.pyi"]

[lsp_servers.heuristics]
project_markers = ["pyproject.toml", "ty.toml"]

Java with jdtls:

[[lsp_servers]]
language_id = "java"
command = "/path/to/jdtls/bin/jdtls"
file_patterns = ["**/*.java"]

Shell scripts with bash-language-server:

[[lsp_servers]]
language_id = "shellscript"
command = "bash-language-server"
args = ["start"]
file_patterns = ["**/*.sh", "**/*.bash"]

C and C++ with clangd options:

[[lsp_servers]]
language_id = "cpp"
command = "clangd"
args = ["--background-index", "--clang-tidy"]
file_patterns = ["**/*.c", "**/*.cpp", "**/*.cc", "**/*.h", "**/*.hpp"]

[lsp_servers.initialization_options]
compilationDatabasePath = "build"

Use the language_id from the default language table; it is the identifier sent to the server when a file is opened.

Files with unusual extensions

mcpls knows 30 languages by extension. To teach it another, add a mapping and a server for it:

[[workspace.language_extensions]]
extensions = ["nu"]
language_id = "nushell"

[[lsp_servers]]
language_id = "nushell"
command = "nu"
args = ["--lsp"]
file_patterns = ["**/*.nu"]

Extensions are written without the dot and are case-sensitive. If you supply any language_extensions, list every language you need, because your list replaces the defaults.

Monorepos

file_patterns cannot confine a server to a subdirectory, because routing uses the extension only. Scope servers by project instead, with workspace.roots and heuristics.project_markers:

[workspace]
roots = ["/work/monorepo/backend", "/work/monorepo/frontend"]

[[lsp_servers]]
language_id = "rust"
command = "rust-analyzer"
file_patterns = ["**/*.rs"]

[lsp_servers.heuristics]
project_markers = ["Cargo.toml"]

[[lsp_servers]]
language_id = "typescript"
command = "typescript-language-server"
args = ["--stdio"]
file_patterns = ["**/*.ts", "**/*.tsx"]

[lsp_servers.heuristics]
project_markers = ["package.json"]

What servers can and cannot do

Not every server supports every tool. rust-analyzer advertises neither type hierarchy nor range formatting, and typescript-language-server does not advertise type hierarchy. The get_tool_support tool reports, per language, which tools are usable, so you can check before you call them.

What’s Next

Now tour what the 31 tools can do.