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 skills add slicervm/agent-skills --skill use-xvfb-terminal-recordinggit clone --depth 1 https://github.com/slicervm/agent-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/slicervm/agent-skills/use-xvfb-terminal-recording)<a href="https://agentmods.dev/skills/slicervm/agent-skills/use-xvfb-terminal-recording"><img src="https://agentmods.dev/badge/skills/slicervm/agent-skills/use-xvfb-terminal-recording/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/slicervm/agent-skills/use-xvfb-terminal-recording"><img src="https://agentmods.dev/badge/skills/slicervm/agent-skills/use-xvfb-terminal-recording.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What 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 5.1 | $0.00079 | $0.03854 |
| Opus 5 | $0.00039 | $0.01927 |
| Sonnet 5 | $0.00016 | $0.00771 |
| Haiku 4.5 | $0.00008 | $0.00385 |
Grade B, and why
use-xvfb-terminal-recording scanned grade B with 2 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 5d 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.
Sends data to an external URLmediumData exfiltration
A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.
`send-keys` string like a `curl … -d '{"cmd":"…"}'` is re-quoted by your Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
`send-keys` string like a `curl … -d '{"cmd":"…"}'` is re-quoted by your How it starts
The opening of the file, as written. The whole thing — 283 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Use Xvfb Terminal Recording — real video of a real terminal
Render the terminal with a real terminal emulator (xterm) on a real X
server (Xvfb) and capture the screen with ffmpeg, exactly as a human would
see it. Do NOT hand-render frames from an asciinema cast or tmux capture-pane + Pillow: re-implementing a terminal emulator and font
rasteriser produces broken output (tofu holes, glyph shear, dropped
timing).
Verified on Slicer VMs (Ubuntu 22.04) 2026-08-14/15. Companion skill for the
two-VM side-by-side variant on a host display: use-dual-terminal-race.
Prerequisites (install once in the VM, as root)
DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
xvfb xterm fonts-dejavu-core ffmpeg x11-utils imagemagick
x11-utils gives xwininfo (window geometry), imagemagick gives import
(stills).
Step 1 — Start Xvfb
# as uid 1000; must persist across execs — bg exec or setsid
DISPLAY=:99 Xvfb :99 -screen 0 1920x1080x24 -ac +extension GLX +render -noreset &
Verify: pgrep -a Xvfb and ls /tmp/.X11-unix/ → X99.
Step 2 — Build the tmux layout
One tmux session per agent/pane (not two panes of one session) so tools that address agents by session work:
tmux new-session -d -s left -x 73 -y 41
tmux new-session -d -s right -x 72 -y 41
tmux send-keys -t left 'cd ~ && clear' Enter
tmux send-keys -t right 'cd ~ && clear' Enter
# launch the agent in each — WITH auto-approval:
tmux send-keys -t left 'opencode --auto -m provider/model' Enter
tmux send-keys -t right 'opencode --auto -m provider/model' Enter
Two shells side by side — prefer one split session
The per-session layout above is for agent demos, where tools address each agent by session name. For a plain two-shell split screen (a service on the left, a client driving it on the right) use ONE session with two panes instead, and one wide xterm:
tmux new-session -d -s demo -x 200 -y 50
tmux split-window -h -t demo
tmux setw -t demo synchronize-panes off # ensure keystrokes are NOT mirrored
# address panes by explicit session:window.pane, and verify they are
# independent BEFORE recording:
tmux send-keys -t demo:0.0 'AAA'; tmux send-keys -t demo:0.1 'BBB'
tmux capture-pane -t demo:0.0 -p | tail -1 # must show AAA only
tmux capture-pane -t demo:0.1 -p | tail -1 # must show BBB only
What ships with it
1 file 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.
- 5d ago Changed · +90 lines scan A → B 516c9006ce93
- 11d ago First seen · 193 lines · 79 tokens per session scan A 39155bfd4530
use-xvfb-terminal-recording is a skill published in the GitHub repository slicervm/agent-skills (5 stars, last pushed yesterday), licensed MIT. It adds 79 tokens to every session and 3,854 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it B with 2 findings (sends data to an external url, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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