Calva Backseat Driver MCP
A VS Code extension that gives agents the Clojure REPL and structural form editing with built-in bracket balancing.
- 66 ★ on the repository
- Last commit
- MIT
Extended access
Why this level
- The agent runs code in the project REPL and edits files in the VS Code workspace.
Install
- Works in
Manual install
Install the Calva Backseat Driver extension from the VS Code marketplace, run the start MCP socket command and connect the client following `MCP-CONFIGURATION.md`. Copilot and Cursor need no setup.
Access and checks
How we reviewExtended accessThe tool runs code or makes network calls and only reads external data.
- The agent runs code in the project REPL and edits files in the VS Code workspace.
This is third-party code. Review the repository files before installing.
What it does
Calva Backseat Driver connects an AI agent to Calva tools inside VS Code. The agent evaluates code in the active REPL, loads files, and creates or edits Clojure files by top-level form, with Parinfer balancing brackets. ClojureDocs lookup and output log reading are included. GitHub Copilot and Cursor see the tools with no setup. Other agents connect through an MCP socket and a small Node wrapper. Two skills ship with it: REPL discipline and structural code editing.
Who it is for. Clojure and ClojureScript developers who work in VS Code with Calva and want the agent to use the REPL instead of guessing results.
Good fit when
- An agent edits a function in a `.clj` file and brackets must stay balanced.
- A hypothesis needs testing in the live project REPL rather than by reading code.
- A shadow-cljs project where the agent reaches builds and the runtime.
- A team attaches several agents to one VS Code window, such as Cursor and Claude Code.
Not a fit when
- The editor is not VS Code or a fork of it.
- The project has no Calva and no running REPL.
- The code is in another language and does not need structural form editing.
Example request
Evaluate the expression in the active REPL, then replace the top-level form `handle-request` and show that brackets are balanced.MCP
- Transport
- stdio
- Authentication
- not required
Limitations
It works only inside a VS Code window with Calva installed. Each window runs its own MCP server, and the port and port-file path change when the project is opened in another editor or workspace. The agent evaluates code in your REPL with the project process permissions, so watch which sessions are attached. Evaluation result size is capped by `maxLength` and `maxDepth`, and deep structures are truncated. Windsurf has no instructions in the documentation yet.
How to disable. Stop the MCP socket with the extension command, remove the server entry from the client config and disable the extension in VS Code. Automatic Cursor and ECA registration is switched off with `autoRegisterCursorMcp` and `autoRegisterEcaMcp`.
FAQ
Does Cursor need any setup?
No. The extension registers the server itself as `extension-backseat-driver`. Set `autoRegisterCursorMcp` to false to turn automatic registration off.
How do I connect Claude Desktop?
Start the MCP socket in VS Code, copy the command with the port file from the dialog and paste it into the global Claude Desktop config as a `node` server.
How do I limit REPL result size?
The `evaluation.maxLength` (default 25) and `evaluation.maxDepth` (default 7) settings truncate collections and nesting. A value of 0 turns the limit off.
What skills come with it?
The Backseat Driver skill teaches REPL work and the structural editing skill covers top-level form edits. Disable them with `provideBdSkill` and `provideEditSkill`.
Where do I get Clojure style rules for the agent?
The Awesome Backseat Driver repository has plugins and skills for Copilot and Cursor. For other agents they are copied by hand.
Discussion
No questions or reviews yet.
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README in short
The extension exposes Calva to agents: REPL, structural editing, bracket balancing and ClojureDocs lookup. Extra skills describe REPL discipline.