LSP

Use this Caplet to expose Language Server Protocol capabilities through language-server-mcp without handing every language-server operation to an agent up front.

The server runs over stdio, starts local language servers lazily, and gives agents project-aware code intelligence for repositories that have LSP configuration or supported built-in language servers.

Project Binding is required because all useful LSP operations need a trustworthy bound project root for workspace-relative files, language-server startup, diagnostics, and edit containment.

Good Fits

• Inspect hover/type information before editing unfamiliar code.
• Jump to definitions, declarations, implementations, and type definitions.
• Find references and document/workspace symbols during refactors.
• Read diagnostics from configured language servers before proposing fixes.
• Request formatting, code actions, rename edits, and workspace edits.
• Cross-check code review or planning assumptions with language-server-backed facts.

Setup

Create a project-level .lsp-mcp.jsonc when the defaults are not enough:

{
  "lsp": {
    "servers": {
      "typescript": {
        "registry": "typescript",
      },
    },
  },
}

For file-targeted tools, pass absolute or workspace-relative paths that resolve inside the workspace. A typical request includes workspaceRoot, filePath, line, and character:

{
  "workspaceRoot": "/absolute/path/to/project",
  "filePath": "/absolute/path/to/project/src/index.ts",
  "line": 3,
  "character": 12
}

serverId is optional for file-targeted tools. When omitted, language-server-mcp runs against configured or built-in servers whose language IDs or file extensions match the file. Add "serverId": "typescript" to force a specific server.

Built-in registry IDs include common servers such as typescript, deno, eslint, json, pyright, gopls, rust, svelte, vue, yaml-ls, bash, clangd, lua-ls, and terraform. Mason and nvim-lspconfig aliases such as ts_ls, denols, yamlls, bashls, rust_analyzer, and compatibility aliases such as python, go, and yaml are also accepted by the downstream server.

Safety

language-server-mcp defaults to conservative behavior for file modification and process execution:

• Edit-producing tools return edits by default and do not write files unless apply: true is passed.
• apply: true requires serverId when more than one matching LSP server would produce edits.
• Applied edits are restricted to the workspace root unless the downstream server is configured with security.allowExternalFiles: true.
• workspace/executeCommand is enabled by default, but can be disabled globally or restricted with per-server command allowlists.
• LSP servers start lazily on first use and stop after an idle timeout by default.
• Managed downloads are available only for supported built-ins and can be disabled with downloads.enabled: false.

Examples

Ask for hover information at a symbol:

{
  "workspaceRoot": "/absolute/path/to/project",
  "filePath": "/absolute/path/to/project/src/index.ts",
  "line": 10,
  "character": 18,
  "serverId": "typescript"
}

Read diagnostics for a source file:

{
  "workspaceRoot": "/absolute/path/to/project",
  "filePath": "/absolute/path/to/project/src/index.ts"
}

Request code actions without applying edits immediately:

{
  "workspaceRoot": "/absolute/path/to/project",
  "filePath": "/absolute/path/to/project/src/index.ts",
  "range": {
    "start": { "line": 12, "character": 0 },
    "end": { "line": 12, "character": 24 }
  },
  "apply": false,
  "serverId": "typescript"
}