Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/understudy-ai/understudy/tmuxnpx skills add understudy-ai/understudy --skill tmuxgit clone --depth 1 https://github.com/understudy-ai/understudyWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00022 | $0.00963 |
| Opus 5 | $0.00011 | $0.00481 |
| Sonnet 5 | $0.00004 | $0.00193 |
| Haiku 4.5 | $0.00002 | $0.00096 |
Grade A, and why
tmux scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
86% identical to tmux — 19 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.
tmux Session Control
Control tmux sessions by sending keystrokes and reading output. Essential for managing Claude Code sessions.
When to Use
✅ USE this skill when:
- Monitoring Claude/Codex sessions in tmux
- Sending input to interactive terminal applications
- Scraping output from long-running processes in tmux
- Navigating tmux panes/windows programmatically
- Checking on background work in existing sessions
When NOT to Use
❌ DON'T use this skill when:
- Running one-off shell commands → use
exectool directly - Starting new background processes → use
execwithbackground:true - Non-interactive scripts → use
exectool - The process isn't in tmux
- You need to create a new tmux session → use
execwithtmux new-session
Example Sessions
| Session | Purpose |
|---|---|
shared |
Primary interactive session |
worker-2 - worker-8 |
Parallel worker sessions |
Common Commands
List Sessions
tmux list-sessions
tmux ls
Capture Output
# Last 20 lines of pane
tmux capture-pane -t shared -p | tail -20
# Entire scrollback
tmux capture-pane -t shared -p -S -
# Specific pane in window
tmux capture-pane -t shared:0.0 -p
Send Keys
# Send text (doesn't press Enter)
tmux send-keys -t shared "hello"
# Send text + Enter
tmux send-keys -t shared "y" Enter
# Send special keys
tmux send-keys -t shared Enter
tmux send-keys -t shared Escape
tmux send-keys -t shared C-c # Ctrl+C
tmux send-keys -t shared C-d # Ctrl+D (EOF)
tmux send-keys -t shared C-z # Ctrl+Z (suspend)
Window/Pane Navigation
# Select window
tmux select-window -t shared:0
# Select pane
tmux select-pane -t shared:0.1
# List windows
tmux list-windows -t shared
Session Management
# Create new session
tmux new-session -d -s newsession
# Kill session
tmux kill-session -t sessionname
# Rename session
tmux rename-session -t old new
What ships with it
2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 154 lines · 22 tokens per session scan A d1d87b8897d7
tmux is a skill published in the GitHub repository understudy-ai/understudy (456 stars, last pushed 2mo ago), licensed MIT. It adds 22 tokens to every session and 963 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 86% identical to tmux, differing in 19 lines, and is treated as a copy.
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