Phonebook, a new tool showcased on Hacker News, enables direct communication between separate running Claude Code sessions. By allowing one session to query another, it addresses the persistent challenge of maintaining context across different projects or teammates' workspaces. The tool facilitates this via a shared channel where an 'asking' session can request information from an 'answering' session, which then queries its own local repository and returns the result.

How It Works

The mechanism relies on explicit registration and approval. Users must run npx agent-phonebook@0.4.1 setup in their project directories and start Claude with npx agent-phonebook@0.4.1 claude. To enable cross-session queries, the answering session must be registered with a specific topic (e.g., job-retries) and explicitly approve the sender's email address. The asking session then directs a query to that topic, and the response is delivered as an event within the active Claude session.

Security and Privacy Constraints

Phonebook imposes strict boundaries to prevent data leakage. While email sign-in is required, it does not connect to GitHub. Questions and replies are not end-to-end encrypted and are retained for up to 7 days. Crucially, registration details such as name, description, and topics are public, though emails remain hidden. The tool warns that topics do not sandbox the answering session's context; therefore, users are advised to use only trusted people and non-sensitive projects.

Technical Requirements

The tool currently requires Node.js 24 and is tested on macOS, with Linux support via automated tests. Windows is explicitly unsupported. The workflow involves a two-pane terminal interaction where tool calls in the answering session require manual approval, ensuring that the AI does not execute commands without human oversight. This design choice highlights the tension between autonomous agent utility and security in shared environments.

Key Takeaways

  • Phonebook enables cross-project context sharing for Claude Code by routing queries between active sessions.
  • Security relies on manual approval for tool calls and explicit sender registration, with no end-to-end encryption.
  • The tool is currently limited to macOS and Linux, requiring Node.js 24.
  • Data retention for questions and replies is up to 7 days, with public visibility of registration topics.

The Bottom Line

Phonebook is a necessary bridge for the fragmented reality of modern AI-assisted development, but its manual approval overhead and lack of E2E encryption mean it is best suited for trusted, non-sensitive workflows rather than open-team collaboration.