# Vellum Terminal Sessions

> Manage persistent tmux terminal sessions: create, read, write to, list, and close named shell sessions. For Claude Code or Codex, use the ACP skill instead.

- Skill: `vellum-ai/vellum-terminal-sessions` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds@latest add vellum-ai/vellum-terminal-sessions`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vellum-ai/vellum-terminal-sessions/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: vellum-ai (https://skillmd.com/u/vellum-ai)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/vellum-ai/vellum-terminal-sessions

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## Overview

This skill manages **persistent terminal sessions** via tmux. Two modes:

|                       | Sandbox Mode                                  | Host Mode                                                           |
| --------------------- | --------------------------------------------- | ------------------------------------------------------------------- |
| **Where tmux runs**   | In the assistant's sandbox                    | On the user's host machine                                          |
| **How user connects** | `vellum terminal attach <session-name>`       | User opens their own terminal                                       |
| **Assistant access**  | Direct (`bash` tool)                          | Via `host_bash`                                                     |
| **Best for**          | Long-running builds, servers, always-on tasks | Work needing host access (e.g. SwiftUI builds, host-local services) |

**Default:** Use **Sandbox Mode** unless the task specifically requires host access. Details: [sandbox-sessions.md](references/sandbox-sessions.md) · [host-sessions.md](references/host-sessions.md) · [tmux-best-practices.md](references/tmux-best-practices.md)

## Prerequisites

**Sandbox Mode:** No setup needed — tmux is available in the sandbox.

**Host Mode:** Requires tmux on the host — see [host-sessions.md](references/host-sessions.md).

## Workflow: Orchestrating Multiple Sessions

- **List** all sessions: `tmux list-sessions` to get names and current commands
- **Read** each: `tmux capture-pane -t NAME -p -S -50` (30-50 lines is usually enough)
- **Summarize** before acting: "Build done, tests at 73%, deploy waiting for confirmation"
- **Act** on the user's instructions