LSP Server

The bifrost command no longer serves the Language Server Protocol (LSP). The language server is a separate program named bifrost-lsp. It comes from the BrokkAi/bifrost-lsp repository.

Which Bifrost Versions Serve LSP

Bifrost build	`bifrost --lsp`
Released 0.12.0 and earlier	Serves LSP over stdio.
Built from later source, including development builds that still report version 0.12.0	Prints `the LSP server has moved out of this repository` and exits with status 1.

bifrost --server lsp behaves the same way as bifrost --lsp. Until a bifrost-lsp release exists, you have two working options:

In VS Code or Cursor, install the published extension. It downloads its own Bifrost 0.11.5 binary. See VS Code LSP.
In another editor, start a released Bifrost 0.12.0 or earlier binary with bifrost --root <workspace-root> --lsp.

The Claude Code agent plugin registers an LSP server that runs bifrost --lsp. It works only with the plugin’s pinned release, Bifrost 0.12.0. See Claude Code.

Launch Command

Editors start the server as a child process and talk to it over stdin and stdout:

bifrost-lsp --root <workspace-root>

--root names the fallback workspace root. The VS Code extension passes the first workspace folder. It also appends the strings from its bifrost.extraArgs setting after --root. The extension runs bifrost-lsp --version to check a downloaded binary before it starts the server.

These are the only command-line arguments that the published sources show. The server’s full option list is not published yet.

Environment Variables

The VS Code extension sets these variables when it starts bifrost-lsp. The bifrost CLI does not read them.

Variable	Value the extension sets	Meaning
`BIFROST_LSP_DEBUG`	`1` when `bifrost.debug` is on; otherwise the inherited value, or `0`	Log the start and end of every LSP request and notification.
`BIFROST_LSP_SLOW_MS`	The `bifrost.slowRequestMs` setting; default `2000`	Log requests and notifications that take at least this many milliseconds.
`RUST_BACKTRACE`	The inherited value, or `1`	Print a backtrace if the server panics.

The VS Code extension copies the server’s stderr to Output > Bifrost. In other editors, look for stderr in the editor’s language-server log.

Initialization Options

The VS Code extension sends this object as the LSP initializationOptions. It sends the same object when the server requests the bifrost section through workspace/configuration.

Field	Type	Meaning
`roots`	array of absolute paths	Directories to index instead of the whole workspace. An empty array means the whole workspace.
`exclude`	array of absolute paths	Files or directories to leave out of indexing and lookups.
`formatterCommands`	array of formatter rules	External formatters to run for document formatting. See VS Code LSP for the rule fields.
`unrecognizedSymbolDiagnostics`	boolean	Report symbols and members that Bifrost cannot resolve. Experimental. Default `false`.

The extension turns relative paths in its settings into absolute paths before it sends them. When you configure another editor, send absolute paths too.

Versions and the Compatibility Check

Three version numbers are independent of each other:

Version	Where it comes from	Current value in the bifrost-lsp source
Extension version	The VS Code extension’s `version`	`0.12.0` (not published)
Server version	The `bifrost-lsp` release tag, `v<server>`	Preferred `0.1.0`, minimum `0.1.0`
Engine version	The Bifrost analysis engine built into `bifrost-lsp`	The extension accepts `>=0.11.0 <1.0.0`

When the server starts, it must identify itself in its initialize result:

{
  "capabilities": {
    "experimental": {
      "bifrost": {
        "protocolVersion": 1,
        "engineVersion": "0.12.0"
      }
    }
  }
}

protocolVersion must be 1. engineVersion must be a three-part version inside the extension’s engine range. If either value is missing, malformed, or out of range, the extension stops the server and shows the error in its status bar item and output channel. Other editors do not run this check.

Release Files

Each bifrost-lsp release on GitHub will contain one archive and one SHA-256 file for each platform:

Platform	Archive
macOS (Intel and Apple silicon)	`bifrost-lsp-v<server>-universal-apple-darwin.tar.gz`
Linux x64	`bifrost-lsp-v<server>-x86_64-unknown-linux-gnu.tar.gz`
Linux arm64	`bifrost-lsp-v<server>-aarch64-unknown-linux-gnu.tar.gz`
Windows x64	`bifrost-lsp-v<server>-x86_64-pc-windows-msvc.zip`
Windows arm64	`bifrost-lsp-v<server>-aarch64-pc-windows-msvc.zip`

The checksum file has the archive name plus .sha256. The archive contains a top-level directory with the archive’s base name and the bifrost-lsp executable (bifrost-lsp.exe on Windows) inside it.

Editor Setup

Use MCP for Agents

Agents do not need the language server. Bifrost’s code intelligence for agents runs over the Model Context Protocol (MCP) from the bifrost command:

bifrost --root /path/to/project --mcp searchtools

See Claude Code and OpenCode for host setup, and Capabilities for what the tools answer. For terminal checks and scripts, use one-shot CLI tool mode.