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AI Screenshots

Jotain can render the current frame to an image file so an AI assistant (or you) can see how Emacs looks. The capture uses the built-in x-export-frames, which draws the frame straight to PNG/SVG/PDF on cairo builds — no external screenshot tool, no window-manager wrangling. The technique follows Automating Emacs Screenshots (Emacs Redux). Two entry points share the same code path: an interactive command for live sessions, and a headless just recipe for terminal-only environments such as CI or a cloud agent container.

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M-x jotain-screenshot

Captures the selected frame and writes it to var/screenshots/<timestamp>.png (the path is echoed and pushed onto the kill ring). From Lisp, both the output file and the format are parameters:
The command needs a graphical frame on a cairo build (the default Linux X11 build; pgtk also carries cairo). It signals a user-error on tty frames and on builds without x-export-frames — noGui (nix-on-droid) and the macOS NS/macport ports.

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The emacs_screenshot MCP tool

init-ai.el registers the command as a custom MCP tool with claude-code-ide, so a Claude Code session attached to Emacs (C-c C-') can call emacs_screenshot, get back the image path, and read the file to see the frame. For the tool to be served, claude-code-ide-enable-mcp-server must be non-nil — Jotain now sets it in the claude-code-ide block. This starts a small local MCP server per Claude session (loopback only); it also enables claude-code-ide’s built-in Emacs tools for the session. A typical exchange: ask Claude “take a screenshot and check the mode line” — it calls emacs_screenshot, then views the returned PNG.

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Headless: just screenshot

For environments with no display at all — CI, a cloud agent container, an SSH box — the screenshot recipe builds Emacs via Nix, launches it with this repo’s config under a virtual X server (Xvfb, 1920×1080), captures the frame once startup settles, and exits:
xvfb-run comes from the devenv shell (Linux only — Xvfb is X11, and the macOS ports lack x-export-frames anyway). Exit status is 0 on success, 2 if init or the capture failed, non-zero from timeout if the run wedged. Caveats:
  • First run is slow. It pays a full nix-build (binary-cache pull of a multi-GB closure) plus the MELPA bootstrap of every package during init, and needs network for both. The recipe wraps the run in timeout 600; raise it if a cold cache needs more.
  • Fonts may differ. If fontconfig doesn’t see the devenv-shell fonts, Xvfb falls back to whatever is available — the capture still succeeds, just less faithful to your desktop.
  • var/screenshots/ lives under var/, so it is gitignored and wiped by just clean-all.
Last modified on July 16, 2026