Use Holaryn in Visual Studio Code

Use Holaryn in Visual Studio Code

The Holaryn reference extension runs coding sessions inside Visual Studio Code over stable ACP v1.
It does not need the Holaryn Web UI, and it never stores model-provider credentials.

Install the reference extension

First install Holaryn and configure at least one chat model:

uv sync
uv run holaryn --version
holaryn onboard start
holaryn --version

Download the holaryn-agent-vscode.vsix asset from the same Nightly, Beta, or Stable GitHub release
as your Holaryn CLI. In Visual Studio Code:

1. Open Extensions.
2. Open the … menu at the top of the Extensions view.
3. Choose Install from VSIX….
4. Select holaryn-agent-vscode.vsix.
5. Reload Visual Studio Code when prompted.

For a checkout build, run npm ci and npm run package in editors/vscode.

Configure and start

Open a folder or multi-root workspace, then select the Holaryn icon in the Activity Bar. Run
Holaryn: New Coding Session. The extension starts holaryn acp serve --stdio locally and creates a
fresh process-only authentication token.

If holaryn is not on Visual Studio Code's PATH, open Settings, search for Holaryn ACP Executable,
and enter the full executable path. Optionally set Holaryn ACP State Directory to use a specific
Holaryn state directory.

Available commands include:

• Holaryn: New Coding Session and Holaryn: Attach to Session;
• Holaryn: Send Prompt, Holaryn: Steer Active Run, and Holaryn: Cancel Active Run;
• Holaryn: Select Mode, Holaryn: Select Model, and Holaryn: Select Profile;
• Holaryn: Show Session Output.

The extension remembers the workspace's last session and durable event cursor. Reopening the
workspace reattaches without requiring the old Web UI process.

Context, edits, and permissions

Each prompt can include a bounded snapshot of the active selection, open files, diagnostics,
symbols, Git state, and repository instruction files. Likely credentials are redacted before the
snapshot leaves Visual Studio Code. The snapshot is always marked untrusted.

Holaryn checks a file's base SHA-256 immediately before committing an edit. If you changed the editor
buffer after the prompt began, Holaryn refuses the stale overwrite and reports a conflict. Save or
refresh the file, inspect the desired change, and retry.

Tools, files, and terminal actions still use the ordinary Holaryn policy. When approval is required,
Visual Studio Code shows a modal with the exact action and server-computed consequence. Choose the
one-shot allow or reject option with the keyboard; closing the modal rejects the request.

Troubleshooting

• Executable not found: set Holaryn ACP Executable to an absolute path and run
  holaryn --version in Visual Studio Code's integrated terminal.
• Authentication failed: stop the session and reconnect. Tokens are intentionally short-lived
  and cannot be reused from another process.
• Protocol version mismatch: install the VSIX and Holaryn CLI from the same release. Holaryn
  supports stable ACP v1 and reports the requested/supported versions.
• No model is configured: run holaryn onboard start, then attach to the existing session again.
• A file was omitted: large files and total editor context are bounded. Holaryn can request an
  in-workspace file lazily when needed.
• Need protocol logs: run Holaryn: Show Session Output. Standard ACP messages never share the
  log stream.

Remote ACP is intentionally not exposed by this extension. Advanced operators can use Holaryn's
documented TLS 1.3 and mutual-TLS transport; see
the protocol guide.