Tandem

Tandem lets you annotate code in VS Code and follow walks through it written by a coding agent. Collect questions as you read, review proposed changes beside the code, and copy your annotations and review back to the agent.

Installation

Install Tandem from the Visual Studio Marketplace, or run:

code --install-extension saiashirwad.tandem

Requires VS Code 1.138 or later and a trusted workspace folder on disk. In a multi-root workspace, Tandem uses the first folder. Virtual workspaces and vscode.dev are not supported.

Annotations

Select some code and press Alt+A. Type your annotation and press Enter to save it. Annotations appear as native comment threads beside the code and in VS Code's Comments panel.

• To add to an existing thread, place the cursor inside its range with nothing selected and press Alt+A.
• To annotate a whole file, use Annotate File in the editor title bar or the explorer context menu.
• To edit or delete an annotation, use the buttons on the annotation.

Run Copy Tandem Session to copy all your annotations, with file paths and code snippets, ready to paste into an agent. Snippets keep the code as it was when you annotated it, even if the file changes later.

Clear Tandem Session deletes all annotations. Both commands are available in the Comments panel title bar and the command palette.

Walks

A walk is a sequence of steps an agent writes to explain code, propose changes, or both. Each step can point to code in your project, include a diagram, and link to other files.

To try one, give your agent this prompt:

Write a Tandem walk explaining this project's main execution path. Follow https://github.com/saiashirwad/tandem/blob/main/WALKS.md and save it to .tandem/walk.json. Use a few focused steps with real file paths and unique, exact code quotes.

Open Walk in the activity bar. Click a step to open its file and highlight the relevant code, or use Alt+] and Alt+[ to move between steps. Tandem remembers your place when you leave and come back. Saving a new version of the walk updates the view.

The example walks follow Tandem's own source code.

Reviewing proposals

A proposal describes a change the agent intends to make. If it includes a diff, Open diff opens it in VS Code's diff editor. Viewing or approving a proposal does not change your files.

Use Approve this change to approve a proposal, or press Alt+Enter on the focused step. You can write a response below any step, whether it proposes a change or explains existing code.

When you're done, Submit Review copies your approvals, responses, and annotations to the clipboard. Paste them back into the agent. The review is also saved to .tandem/review.json for the agent to read.

Your review survives reloads. When the agent revises a walk, responses follow their steps and changed proposals lose their approvals. Submitting a review clears nothing.

Tandem works through workspace files and copied text. The extension needs no agent account or API key. See Writing walks for the format and instructions for agents.

Commands

Commands are available in the command palette under Tandem.

Workspace data

Tandem stores its files in .tandem/ at the workspace root:

• session.json — your annotations.
• walk.json — the agent's walk.
• review.json — your approvals and responses.

Tandem adds this folder to .git/info/exclude, leaving your project's .gitignore unchanged. Clearing annotations leaves the walk alone; clearing the walk leaves annotations alone.

Development

Install Node.js 24 or later and Bun 1.4.0, then run:

bun install --frozen-lockfile
bun run build

Press F5 to open an Extension Development Host. To use the extension in your regular window, run Developer: Install Extension from Location… and select this folder. Run bun run watch while editing, then Developer: Reload Window after rebuilding.

bun run package runs type, lint, and formatting checks and builds a self-contained VSIX in dist/. Install it with Extensions: Install from VSIX…. Users do not need Bun or a separate Node.js installation. CI also produces a downloadable VSIX on pushes to main and pull requests.

Before releasing, try annotations, walks, diagrams, diffs, review submission, and persistence after reload in a fresh VS Code profile, including on the minimum supported version. Upload updates through the Marketplace publisher page.

Feedback

Report a bug or request a feature.

License

MIT