headless terminal

Examples · Install · Agent Skill · Commands · Architecture

Puppeteer for terminal UIs. Drive vim, emacs, htop, nethack, or any other interactive TUI from a CLI (or an AI agent) — spawn the program in a background session, send keystrokes, snapshot the screen, and watch the whole thing live from another shell.

Under the hood: a Unix-socket daemon owns a pseudo-terminal per session and pipes its output through libghostty-vt for VT parsing. You get the terminal emulation used by the Ghostty app, in a detached, scriptable, snapshot-able form.

Why

Interactive TUIs assume a human at a keyboard. If you want an agent — or a test, or a debugger, or a recorder — to drive one, you need three things the shell doesn't give you:

• A pseudo-terminal so the TUI thinks it's attached to a real tty.
• A VT parser that tracks cursor position, scrollback, styles, etc. from the TUI's output stream.
• Synchronization primitives so the driver knows when the TUI has finished redrawing.

ht is those three things, wrapped in a simple CLI with a daemon.

Examples

Agentic coding. Let an agent drive interactive CLIs it otherwise can't — git add -p, gh auth login, create-next-app, REPLs, debuggers, even vim for surgical edits.

# Start a headless vim session, returns a short session ID.
ht run --name notes vim /tmp/notes.md

# Drive it. Keys use vim-style notation (<CR>, <Esc>, <C-c>, <F1>, …).
ht send notes "ihello from an agent<Esc>:wq<CR>" --view # return view

# Session exited and the file is saved:
cat /tmp/notes.md
# → hello from an agent

# Remove the session completely
ht remove notes

CI tests for TUIs. Script an interactive program in GitHub Actions: run it, send keys, assert against the rendered screen (as text or a PNG snapshot). Covers paths expect/pexpect can't — alternate screen, colors, cursor position.

# Boot a TUI, send keys, fail the build if the screen doesn't match.
ht run --name smoke vim /tmp/demo.md
ht send smoke "ihello from CI<Esc>" --wait-idle 200ms
ht view smoke | grep -q "hello from CI" || { echo "render failed"; exit 1; }
ht send smoke ":q!<CR>"

Demo and doc generation. Record keystroke-perfect asciicasts with ht record, render to GIF via agg, or grab a one-shot PNG of the current frame for a README or bug report.

# Drive a session, then grab a PNG of the current frame for a README or bug report.
ht run --name demo bash
ht send demo "echo 'headless terminal'<CR>" --wait-idle 200ms
ht view demo --format png > screenshot.png
ht stop demo

Follow-along debugging. ht watch streams a session live to another pane, so a human can shoulder-surf whatever an agent (or a detached process) is driving — handy during skill development or pair debugging.

# Pane A: the watcher blocks until a matching session is created.
ht watch nethack-demo

# Pane B (or an agent): create the session the watcher is waiting for.
ht run --size 78x46 --name nethack-demo nethack -u Claude
ht send nethack-demo "y" --wait-duration 150ms --view
# (pane A now shows nethack, live)

Install

brew install montanaflynn/tap/ht

curl -L https://github.com/montanaflynn/headless-terminal/releases/latest/download/ht-v0.1.0-darwin-arm64.tar.gz | tar xz
sudo mv ht /usr/local/bin/

curl -L https://github.com/montanaflynn/headless-terminal/releases/latest/download/ht-v0.1.0-linux-amd64.tar.gz | tar xz
sudo mv ht /usr/local/bin/

curl -L https://github.com/montanaflynn/headless-terminal/releases/latest/download/ht-v0.1.0-linux-arm64.tar.gz | tar xz
sudo mv ht /usr/local/bin/

git clone https://github.com/montanaflynn/headless-terminal
cd headless-terminal
make build

Agent Skill

An ht-aware skill lives in skills/headless-terminal/. It teaches an agent when to reach for ht, the vim-style key notation, the wait-strategy decision tree (the part agents get wrong), and common recipes.

Preferred — skills CLI (handles per-agent paths for Claude Code, Codex, Cursor, Gemini, etc.):

npx skills add montanaflynn/headless-terminal --skill headless-terminal

Fallback — drop it into Claude Code directly:

cp -r skills/headless-terminal ~/.claude/skills/headless-terminal

The skill uses Anthropic's standard skills format — other agent frameworks that consume the same layout can point their loader at skills/headless-terminal/ or copy it into their equivalent directory. Progressive disclosure: only the short SKILL.md is always in context; reference docs load on demand.

Commands

ht run <cmd...>       start a session (returns a session ID)
ht list               list sessions (table in a tty, JSON when piped)
ht view <sid>         snapshot current screen (plain | ansi | html | png | json)
ht send <sid> <keys>  send keystrokes; optional --view / --wait-* / --rate
ht wait <sid> ...     block until a condition is met
ht watch <sid>        live-stream a session; blocks until it exists
ht record <sid>       record session as asciicast (pipe to agg for GIFs)
ht stop <sid>         graceful shutdown (SIGTERM, escalates)
ht kill <sid>         immediate SIGKILL
ht remove <sid>       delete an exited session's record
ht daemon [stop]      manual daemon control (normally auto-started)

Session IDs can be the short 8-hex ID, an unambiguous prefix, or --name.

Key notation

Vim-style. Literals pass through; angle-bracket specials are recognized:

<CR> <Enter> <Esc> <Tab> <BS> <Space> <Del> <Ins>
<Up> <Down> <Left> <Right> <Home> <End> <PageUp> <PageDown>
<F1>…<F12>
<C-x>          ctrl+x (letters a–z only)
<M-x>          meta/alt+x  (alias <A-x>)
<S-Tab>        shift+Tab
<C-M-x>        combine modifiers in any order
<lt>           literal '<'

Send synchronization

The keystroke-to-snapshot problem in a nutshell: the child process hasn't necessarily processed your keys by the time the daemon returns. ht send gives you three ways to deal with this:

• Pacing (default: 20ms/keystroke). The daemon writes one keystroke at a time with a 20ms gap and a trailing gap. Fast TUIs reliably echo their reaction in that window. Override with --rate 10ms or --rate 0.
• --wait-duration DUR: a plain post-send sleep. Use when a single key triggers slow work (character creation in nethack, emacs startup).
• --wait-text/--wait-cursor/--wait-idle/--wait-change/--wait-exit: block on a deterministic condition. Compose with AND — e.g. --wait-text READY --wait-idle 200ms waits for READY to appear AND output to be quiet for 200ms.

All of these are also available as standalone ht wait subcommand flags.

Exit codes

Architecture

┌──────────────────────────────────────────────────────────────┐
│                         ht CLI                               │
│  (run / send / view / watch / wait / list / stop / …)        │
└──────────────────────────────┬───────────────────────────────┘
                               │  Unix socket, JSON lines
┌──────────────────────────────┴───────────────────────────────┐
│                        ht daemon                             │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐        │
│  │ Session      │  │ Session      │  │ Session      │   …    │
│  │ ┌──────────┐ │  │ ┌──────────┐ │  │ ┌──────────┐ │        │
│  │ │ PTY      │ │  │ │ PTY      │ │  │ │ PTY      │ │        │
│  │ │ ↓        │ │  │ │ ↓        │ │  │ │ ↓        │ │        │
│  │ │ vim/etc  │ │  │ │ nethack  │ │  │ │ emacs    │ │        │
│  │ └──────────┘ │  │ └──────────┘ │  │ └──────────┘ │        │
│  │ libghostty-vt│  │ libghostty-vt│  │ libghostty-vt│        │
│  │ (grid)       │  │ (grid)       │  │ (grid)       │        │
│  └──────────────┘  └──────────────┘  └──────────────┘        │
└──────────────────────────────────────────────────────────────┘

Each session owns a PTY master, a libghostty terminal (the authoritative screen model), and a set of subscriber channels for ht watch. All three are serialized behind a single mutex.