VS Code LSP

The language server moved to bifrost-lsp

Bifrost built after release 0.12.0 does not serve LSP: bifrost --lsp exits with an error. The language server is now the separate bifrost-lsp program, and bifrost-lsp has no release yet. The extension version on the marketplaces still works because it downloads its own Bifrost 0.11.5 binary. See LSP Server for the full status.

Install

Install Bifrost: Multi-Language LSP & MCP Server (brokk.bifrost-vscode) from the Visual Studio Marketplace or Open VSX. The extension needs VS Code 1.90 or newer.

Two extension versions matter:

Extension version	Status	Server it starts
0.11.5	Published on both marketplaces on 2026-09-19.	Downloads Bifrost 0.11.5 from the BrokkAi/bifrost GitHub releases and runs bifrost --root <workspace-root> --lsp.
0.12.0	Source in BrokkAi/bifrost-lsp. Not published.	Downloads bifrost-lsp from the BrokkAi/bifrost-lsp GitHub releases and runs bifrost-lsp --root <workspace-root>, followed by any bifrost.extraArgs.

Both versions have the same settings, commands, and views. The rest of this page describes version 0.12.0. Where version 0.11.5 differs, the page says so.

Version 0.12.0 also checks the server’s identity after it starts. The server must report LSP protocol 1 and a Bifrost engine version from 0.11.0 up to, but not including, 1.0.0. Otherwise the extension stops the server. See LSP Server for the check and the release files.

The extension describes its editor features as definitions, references, symbols, hierarchy, rename, diagnostics, completion, and hover. It starts the server for files in these VS Code languages: c, cpp, csharp, go, java, javascript, javascriptreact, kotlin, php, python, rust, scala, typescript, and typescriptreact. It also activates for the three Bifrost languages below.

Launch Modes

bifrost.launchMode chooses the server binary.

Mode	Binary the extension starts
auto (default)	bifrost.serverPath, if you set it to a value other than bifrost. Otherwise the managed binary, if a compatible one is installed or you accept the install prompt. Otherwise a local development build. Otherwise bifrost on PATH.
bundled	The managed binary only. If no compatible managed binary is installed, the extension asks to install it and fails if you decline.
path	bifrost.serverPath, if you set it to a value other than bifrost. Otherwise a local development build. Otherwise bifrost on PATH.

A local development build is target/debug/bifrost or target/release/bifrost two directories above the extension’s own folder. The extension uses the newer of the two. This applies only when you run the extension from a source checkout.

In version 0.12.0, the default bifrost.serverPath value bifrost names the Bifrost CLI, which no longer serves LSP. In path mode, set bifrost.serverPath to the absolute path of a bifrost-lsp binary.

Managed Binary

In auto and bundled mode, the extension manages its own server binary:

• It supports macOS (x64 and arm64), Linux (x64 and arm64), and Windows (x64 and arm64).
• It asks before it downloads. You can choose Update, Not Now (skip this version), or Don’t Ask Again.
• It downloads the archive and its .sha256 file from the GitHub release. It checks that both match the SHA-256 value built into the extension package.
• It stores the binary in VS Code’s global storage for the extension, under binaries/<version>/<platform>-<arch>/.
• It runs the binary with --version before it uses it.
• It reuses a cached binary from the extension’s compatible version range without asking. After a new install, it deletes cached versions outside that range.

Settings

Setting	Type	Default	Meaning
bifrost.launchMode	auto, bundled, or path	auto	How to choose the server binary. See Launch Modes.
bifrost.serverPath	string	bifrost	Path to the server binary, or a command name to find on PATH.
bifrost.debug	boolean	false	Log every LSP request and notification. The extension passes this to the server as BIFROST_LSP_DEBUG.
bifrost.slowRequestMs	number, minimum 0	2000	Log LSP requests and notifications that take at least this many milliseconds. The extension passes this to the server as BIFROST_LSP_SLOW_MS.
bifrost.extraArgs	array of strings	[]	Extra command-line arguments, added after --root <workspace-root>. Blank entries are dropped.
bifrost.roots	array of strings	[]	Directories to index instead of the whole workspace. Relative paths are resolved against the workspace root. Empty means all workspace folders.
bifrost.exclude	array of strings	[]	Files or directories to leave out of indexing and LSP lookups. Relative paths are resolved against the workspace root.
bifrost.formatterCommands	array of formatter rules	[]	External formatter rules, in order. The extension reads this setting from user settings only. See Formatter Rules.
bifrost.unrecognizedSymbolDiagnostics	boolean	false	Report symbols and members that Bifrost cannot resolve. Experimental; it can report false positives.
bifrost.requireSuppressionReason	boolean	false	Require a reason when you suppress a policy finding. Set it in workspace settings to make it a project rule.

Changes to bifrost.launchMode, bifrost.serverPath, bifrost.debug, bifrost.slowRequestMs, and bifrost.extraArgs need a server restart. The extension asks whether to restart now.

Changes to bifrost.roots, bifrost.exclude, bifrost.formatterCommands, and bifrost.unrecognizedSymbolDiagnostics do not cause a restart prompt. The extension gives the current values to the server whenever the server asks for the bifrost configuration section. If a change does not take effect, run Bifrost: Restart Language Server.

For a large repository, limit indexing before you start the server:

{
  "bifrost.roots": ["src", "tests"],
  "bifrost.exclude": ["target", "vendor/generated"]
}

Formatter Rules

Each entry in bifrost.formatterCommands is an object with these fields. Only command is required. Rules run without a shell. The formatter receives the document text on stdin and must write the formatted document to stdout.

Field	Type	Meaning
include	array of strings	Workspace-relative glob patterns that this rule applies to.
exclude	array of strings	Workspace-relative glob patterns that this rule must not apply to.
language	string	Optional Bifrost language filter, such as rust, go, typescript, java, csharp, php, or ruby.
command	string	Executable name or path. It runs directly and is not parsed by a shell.
args	array of strings	Command arguments. Supports the placeholders {file}, {relativeFile}, {workspaceRoot}, and {language}.
cwd	string	Working directory for the formatter. A relative path is resolved against the workspace root. Supports the same placeholders.

The extension ignores formatter rules in workspace or folder settings, because a workspace could otherwise run any program. It writes a message to Output > Bifrost when it ignores them.

Commands

Command	Command ID	What it does
Bifrost: Start Language Server	bifrost.startServer	Start the server.
Bifrost: Stop Language Server	bifrost.stopServer	Stop the server.
Bifrost: Restart Language Server	bifrost.restartServer	Stop and start the server.
Bifrost: Show Output	bifrost.showOutput	Open Output > Bifrost, which shows the launch command, downloads, and server stderr.
Bifrost: Open MCP Setup	bifrost.openMcpSetup	Choose an MCP setup action. See MCP Setup.
Bifrost: Copy MCP Config	bifrost.copyMcpConfig	Copy a generic mcp.json entry to the clipboard.
Bifrost: Run RQL Query	bifrost.runRqlQuery	Run the current .rql editor text. Available from the Play button in the editor title.
Bifrost: Run RQL Policy	bifrost.runRqlPolicy	Run the current .rqlp editor text. Available from the Play button and from the Command Palette in a .rqlp editor.
Bifrost: Clear Policy Results	bifrost.clearRqlPolicyResults	Clear Bifrost Policy Results. Available from that view’s title bar.
Bifrost: Suppress finding…	bifrost.suppressRqlPolicyFinding	Write a suppression for a policy finding. Available from the context menu of a finding in Bifrost Policy Results.
Bifrost: Show Rune IR	bifrost.showRuneIr	Open the Rune IR of the current source file, or of the selection, in a new untitled editor in Bifrost Rune IR mode. Available from the editor context menu and Command Palette.
Bifrost: Open RQL Query Result	bifrost.openRqlQueryResult	Open the source of a query result. Used by the results view.
Bifrost: Open RQL Policy Finding	bifrost.openRqlPolicyFinding	Open the source of a policy finding. Used by the results view.
Bifrost: Open RQL Policy Display Step	bifrost.openRqlPolicyDisplayStep	Open the source of one step of a finding’s display path. Used by the results view.

The last three commands are hidden from the Command Palette. The status bar item shows the server state. Click it to start or restart the server.

Views and Languages

The extension adds two views to the Explorer:

View	Contents
Bifrost Query Results	Results of the last RQL query run, grouped by file.
Bifrost Policy Results	Completion state, findings, and suppression audit of RQL policy runs.

It also adds three languages:

Language	File extension	Purpose
Bifrost RQL	.rql	Rune Query Language queries.
Bifrost RQL Policy	.rqlp	Static-analysis policies and policy endpoints.
Bifrost Rune IR	.rune	Rune IR previews.

Each language has syntax highlighting and its own file icon. The icon shows when your icon theme has no more specific icon. If another extension claims .rql, choose Bifrost RQL with VS Code’s language-mode picker.

See RQL in VS Code for running queries and policies, and for the features that need a running server.

Workspace .gitignore

In version 0.12.0, the extension checks the workspace .gitignore for a line that ignores all of .bifrost. If it finds one, it offers to replace that line with .bifrost/cache/, so that project files under .bifrost/ can be committed. You can choose Replace, Ask Again Later, or Don’t Ask Again.

MCP Setup

Bifrost: Open MCP Setup offers four actions:

• Copy a generic mcp.json entry.
• Copy a Codex CLI command: codex mcp add bifrost -- <command>.
• Copy a Claude Code command: claude mcp add --scope user bifrost -- <command>.
• Open the Bifrost MCP documentation.

The copied entry starts a separate MCP process for the current workspace:

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

The commands run only when you choose them. The extension does not change other programs’ configuration files.

The extension fills in command with the same binary it would start as the language server. In version 0.11.5 that is a Bifrost CLI binary, which serves MCP. In version 0.12.0 it can be the managed bifrost-lsp binary. Whether bifrost-lsp accepts --mcp is not documented. Before you use the copied entry, check that command names a bifrost CLI binary. See Install for ways to install the CLI, and MCP for the toolsets.

The editor’s language server and an agent’s MCP server are separate processes. Do not point an MCP host at the extension’s language server. Installing the extension does not give an agent the query_code tool. See MCP query and RQL availability.