VS Code LSP

Install the extension from the Visual Studio Marketplace.

Requirements:

VS Code 1.90 or newer.
A supported platform for extension-managed Bifrost binary downloads, or a bifrost binary available through one of the launch modes below.

The extension source lives in editors/vscode. It starts Bifrost with:

bifrost --root <workspace-root> --lsp

For extension development:

cd editors/vscode
npm install
npm test

Use the extension setting bifrost.serverPath when testing a locally built Bifrost binary.

The extension associates .rune files with Bifrost Rune IR and uses that language mode for Bifrost: Show Rune IR previews. Canonical kinds, roles, metadata, spans, strings, and ; comments receive syntax highlighting.

RQL Queries

The extension automatically recognizes .rql files as Bifrost RQL and highlights RQL query structure, known forms, literals, and comments. When the Bifrost language server is ready, the Play button in the editor title executes the current query text, including unsaved edits. Results appear in the Bifrost Query Results Explorer view; select a match to open its source range.

See RQL in VS Code for an execution example, scope rules, and the results view. Opening a query file does not start the language server or wait for indexing. If another extension owns .rql in a workspace, use VS Code’s language-mode picker to select Bifrost RQL. The Bifrost helmet is its default file icon when the active VS Code icon theme does not provide a more specific .rql icon.

The Play action runs through the extension’s language-server connection, including unsaved editor text. It is separate from agent MCP: installing the extension does not expose query_code to an agent, and an MCP agent can execute saved RQL only through a query-capable toolset and query_file. See MCP query and RQL availability.

Extension Settings

Setting	Default	Description
`bifrost.launchMode`	`auto`	How to start Bifrost: `auto`, `bundled`, or `path`.
`bifrost.serverPath`	`bifrost`	Path to the `bifrost` binary, or command name to resolve on `PATH`.
`bifrost.debug`	`false`	Enable verbose LSP request and notification tracing.
`bifrost.slowRequestMs`	`2000`	Log LSP requests and notifications that take at least this many milliseconds.
`bifrost.extraArgs`	`[]`	Additional command-line arguments appended when launching the Bifrost LSP server.
`bifrost.roots`	`[]`	Workspace-relative or absolute directories to index instead of the full VS Code workspace. Empty means use VS Code workspace folders.
`bifrost.exclude`	`[]`	Workspace-relative or absolute files or directories to exclude from Bifrost indexing and LSP lookups.
`bifrost.formatterCommands`	`[]`	Ordered formatter command rules passed to Bifrost from user settings only. Rules run without a shell, receive document text on stdin, and write the formatted document to stdout.
`bifrost.unrecognizedSymbolDiagnostics`	`false`	Enable experimental unrecognized-symbol and member diagnostics.

Changes to bifrost.roots, bifrost.exclude, bifrost.formatterCommands, and bifrost.unrecognizedSymbolDiagnostics apply to the running language server without a restart. Root and exclusion changes rebuild the workspace index; formatter changes affect subsequent formatting requests. Removing one of these settings sends its default value so the previous runtime setting is cleared.

Changes to process-launch settings still require a restart: bifrost.launchMode, bifrost.serverPath, bifrost.debug, bifrost.slowRequestMs, and bifrost.extraArgs. The extension prompts before restarting for those settings.

Launch mode behavior:

auto: use bifrost.serverPath when explicitly configured, then the extension-managed binary when available, then a local development binary under target/, then bifrost on PATH.
bundled: require the extension-managed binary for this platform and prompt to install it when missing.
path: use bifrost.serverPath, falling back to bifrost on PATH.

bifrost.formatterCommands entries support:

Field	Description
`include`	Workspace-relative glob patterns this formatter rule applies to.
`exclude`	Workspace-relative glob patterns this formatter rule must not apply to.
`language`	Optional Bifrost language filter, such as `rust`, `go`, `typescript`, `java`, `csharp`, `php`, or `ruby`.
`command`	Executable name or path. This is executed directly and is not shell-parsed.
`args`	Command arguments. Supports `{file}`, `{relativeFile}`, `{workspaceRoot}`, and `{language}` placeholders.
`cwd`	Working directory for the formatter. Relative paths are resolved against the workspace root and support placeholders.

MCP Setup

Run Bifrost: Open MCP Setup from the Command Palette to choose a setup action: copy generic mcp.json, copy a Codex CLI command, copy a Claude Code command, or open the Bifrost MCP docs. Bifrost: Copy MCP Config remains available when you only want the generic JSON entry.

These commands are manual. The extension does not open MCP setup on activation, does not mutate external host configuration, and does not prompt again after dismissal.

The MCP setup commands use the same binary resolution settings as the language server where practical: a configured bifrost.serverPath, the extension-managed binary, a local development build, or bifrost on PATH.

The copied entry uses the current workspace root and starts a separate Bifrost MCP process:

{
  "mcpServers": {
    "bifrost": {
      "command": "/path/to/bifrost",
      "args": ["--root", "/path/to/workspace", "--mcp", "searchtools"]
    }
  }
}

Do not point MCP hosts at the VS Code LSP process. The extension and MCP hosts should launch separate stdio processes from the same Bifrost binary or release.