Capture cmux windows as screenshots or video clips from the CLI. Create visual evidence for pull requests and bug reports, with region selection and captions to explain drags, animations, or layout changes.
Screenshot or record a cmux window from the CLI, for a pull request, a bug report, or to see what the app actually looks like right now. Use when a change is visual, when a drag or an animation cannot be described in text, or when a reviewer needs evidence rather than a claim.
Review the instructions the agent will receive before you install.
cmux shot writes a png or a jpeg of a cmux window. cmux record writes an mp4
or a gif of one. Both capture only cmux's own windows, both go through the
same permission-free path, and both work in a release build and inside CI. No
Screen Recording permission is involved and none is ever requested.
cmux shot --label settings-sheet # png of the frontmost window
cmux shot --jpg --max-width 1200 --out ~/before.jpg
cmux record start --gif --max-seconds 8 --label sidebar-drag
cmux record note "dragging the workspace" # caption, drawn into the clip
cmux record stop
shot prints <width>x<height> <bytes> <path>. record prints
<id> <state> <frames> <path>. Both take --json for the whole response.
Take a screenshot when the thing is still: a sheet, a menu, a layout, a label, a color. Record when the thing is a change over time: a drag, an animation, a reorder, two views settling in an order, a spinner that should stop. A screenshot of a drag shows nothing, and a clip of a static sheet is a large file a reviewer has to click to play.
--region x,y,w,h is the same rectangle in both commands, in window points from
the window's top left. So a detail noticed in a clip can be shot with the same
four numbers:
cmux record start --region 0,0,420,900 --max-seconds 6 # watch the sidebar
cmux shot --region 0,0,420,900 --label sidebar-final # keep the end state
--max-seconds (default 15, maximum 120), so
a clip is never left running by an agent that stops paying attention. Set it
above the time the actions take or the clip ends early.record start is refused with conflict while
one is running. cmux record list says whether anything is going, and
cmux record status reports the frame count, with the effective frame rate
in --json.cmux record note "<text>" draws text into the clip
from that moment on. A clip has no step list beside it, so one note before
each thing a reviewer should notice is worth more than a longer clip.
--no-captions turns them off.fps_effective in --json if a clip looks slower than expected.gif is the shape to paste into a pull request, and --gif already picks
the 8 fps and half scale that keep one small; an mp4 is sharper and needs a
click to play. scripts/pr-media.py uploads either and converts an mp4 to a
gif on the way.--out on a path that is not a file is refused, and so is
one whose extension does not match the format: --out clip.gif needs --gif.A dogfood scenario records with a record step wrapping the steps that matter,
and captions with note, rather than by calling the CLI. The step table and the
options are in
cmux-testing/references/dogfood-scenarios.md.
| Reference | When to use |
|---|---|
| references/commands.md | Every flag, the response shape, the error codes, window selection, limits |
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