Run in MCP mode

BSL Language Server can act as a Model Context Protocol (MCP) server — exposing 1C (BSL) and OneScript code analysis to AI agents and tools that support MCP.

MCP tools run on top of the same engine as the LSP mode: the same parsing, the same providers. Workspaces are provided through MCP roots — the direct analog of LSP workspace folders.

Experimental feature

The MCP mode is built on Spring AI 2.0 (a milestone version at the time of writing). The API and behavior may change.

Run modes

MCP can be exposed in several ways.

Standalone MCP server (the mcp command)

The transport is selected with --protocol: stdio (default), sse or streamable. LSP is not started.

stdio — the standard way to connect local tools:

java -jar bsl-language-server.jar mcp
# same as: java -jar bsl-language-server.jar mcp --protocol stdio

sse — Server-Sent Events over HTTP on a built-in web server (endpoint /sse, messages at /mcp/message):

java -jar bsl-language-server.jar mcp --protocol sse --server.port=8080

streamable — Streamable HTTP over HTTP on a built-in web server (endpoint /mcp):

java -jar bsl-language-server.jar mcp --protocol streamable --server.port=8080

Next to LSP over stdio

LSP stays on stdio, while MCP is additionally exposed over Streamable HTTP on a built-in web server. Enabled with the --mcp flag. The lsp command is the default mode, so it can be omitted:

java -jar bsl-language-server.jar --mcp --server.port=8080
# same as: java -jar bsl-language-server.jar lsp --mcp --server.port=8080

Next to LSP over websocket

LSP over websocket and MCP over Streamable HTTP on the same web server:

java -jar bsl-language-server.jar websocket --mcp --server.port=8080

Workspaces (MCP roots)

Source directories are provided by the client through MCP roots — just like an LSP client sends workspace folders. The server indexes the declared roots into the shared context and re-syncs them on change (roots/list_changed). In the combined modes (lsp --mcp, websocket --mcp) workspaces come from both the LSP client (workspace folders) and the MCP client (roots) into one shared context.

Available tools

Tool	Purpose
analyze_file	Diagnostics for a file
document_symbols	Symbol tree of a file (methods, regions, variables)
find_references	All references to the symbol at a position
call_hierarchy	Incoming and outgoing calls of the method/procedure at a position
hover	Hover info for a symbol (signature, type, documentation)
definition	Go to the symbol declaration
type_info	Properties and methods of a type looked up by name (e.g. Массив/Array)
type_at_position	Inferred type of the expression under the cursor and its available methods and properties

Positions (line, character) are zero-based, as in LSP.

Launch options

Option	Mode	Purpose
-c, --configuration <path>	all	Path to the global configuration file (see Configuration file)
--protocol <stdio\|sse\|streamable>	mcp	Transport of the standalone MCP server: stdio (default), sse or streamable
--mcp	lsp (default), websocket	Also expose MCP over Streamable HTTP
--mcp-path <path>	lsp --mcp, websocket --mcp	MCP endpoint path (default /mcp)
--server.port=<port>	mcp --protocol sse\|streamable, lsp --mcp, websocket --mcp	Port of the built-in web server

Client configuration examples

stdio

The client launches the server itself and talks to it over stdio (mcpServers format):

{
  "mcpServers": {
    "bsl-language-server": {
      "command": "java",
      "args": ["-jar", "/path/to/bsl-language-server.jar", "mcp"]
    }
  }
}

Streamable HTTP

The server is started separately (--mcp or websocket --mcp), and the client connects to the endpoint by URL:

{
  "mcpServers": {
    "bsl-language-server": {
      "type": "streamable-http",
      "url": "http://localhost:8080/mcp"
    }
  }
}

The default address is http://<host>:<port>/mcp; the path is changed with --mcp-path, the port with --server.port.