terminal-screenshot

Terminal Screenshot

Render the colored output of a terminal command into a PNG image, then read that

image to judge the result visually.

Why this exists

When a command's output arrives as a tool result, Claude sees plain text plus raw

escape codes like \x1b[48;2;92;30;34m — not the rendered colors. That makes it

impossible to honestly answer "is the diff's add/remove contrast strong enough?"

or "did this theme come out too dark?". Reading hex values is guessing. This skill

turns the output into an image so the judgement is based on what a human would

actually see on screen.

The method: capture, then render

Two separate steps. Keep them separate — that separation is the whole trick.

Step 1 — Capture full-fidelity ANSI to a file

Most CLIs **drop or downgrade colors when they detect they're not writing to a

real terminal** (a pipe or a child process). Force full coloring and save to a

.ansi file. The exact flag depends on the tool — recipes below.

The single most important rule: never let the renderer run the command for you.

freeze --execute "git diff | delta" looks convenient but produces a degraded

result — delta (and lazygit, and anything that probes terminal capabilities) runs

inside freeze's child pty, detects a reduced environment, and silently drops its

background blocks, line-number column, and header box. Capture in a normal shell

first, render second.

Step 2 — Render the ANSI file to PNG, then read it

Use the bundled wrapper, which prefers freeze and falls back to a stdlib

renderer + headless Chrome:

scripts/render_ansi.sh <input.ansi> <output.png> [background_hex]

Then read the PNG with the Read tool and judge the colors.

Background color must match the real terminal, or a dark theme verified on a

white page looks wrong. On macOS with Ghostty:

ghostty +show-config --default | grep '^background'   # e.g. 282c34 (the default)

Pass it as #282c34. If unknown, a dark terminal is usually near #1d1f21–#282c34.

Capture recipes per tool

Pick a --width close to the real terminal (≈100–120) so wrapping matches.

| Tool | Capture command (writes full-color ANSI) |

|------|------------------------------------------|

| delta (git diff) | git --no-pager diff \| delta --dark --line-numbers --width=110 > /tmp/x.ansi |

| git diff (native) | git -c color.ui=always --no-pager diff > /tmp/x.ansi |

| bat | bat --color=always --style=numbers <file> > /tmp/x.ansi |

| eza | eza -la --color=always --icons > /tmp/x.ansi |

| ls (GNU) | ls -la --color=always > /tmp/x.ansi |

| ls (macOS/BSD) | CLICOLOR_FORCE=1 ls -laG > /tmp/x.ansi |

| ripgrep | rg --color=always 'pattern' <path> > /tmp/x.ansi |

| anything else | CLICOLOR_FORCE=1 <cmd> > /tmp/x.ansi or <cmd> --color=always, or wrap in a real pty: script -q /dev/null <cmd> |

Note delta always emits its configured colors even to a file, so the only trap

for delta is Step 1's rule (don't render it via freeze --execute).

Full example: verify a delta color change

# after editing [delta] colors in gitconfig, in any repo with a diff:
git --no-pager diff | delta --dark --line-numbers --width=110 > /tmp/diff.ansi
scripts/render_ansi.sh /tmp/diff.ansi /tmp/diff.png "#282c34"
# then: Read /tmp/diff.png and judge whether add/remove contrast is clear

TUI programs (lazygit, htop, top) — out of scope

Full-screen TUIs paint with cursor positioning, not a linear ANSI stream, so they

can't be captured this way. To check a TUI's colors, verify the underlying piece

in isolation — e.g. for lazygit's diff, render git diff | delta as above (lazygit

calls the same delta config). For a true TUI screenshot, run it in a real terminal

and capture the screen (a screencapture/computer-use task), not this skill.

Installing freeze (the preferred renderer)

freeze is charmbracelet/freeze — it

renders ANSI to PNG/SVG/WebP with faithful background blocks and nice chrome.

Do not run brew install freeze — that installs an unrelated GUI app of the

same name (a cask). The CLI lives in charmbracelet's tap or via go install:

# Option A — Homebrew tap (needs GitHub reachable)
brew install charmbracelet/tap/freeze

# Option B — go install (works behind a firewall via a Go module mirror)
GOPROXY=https://goproxy.cn,direct GOSUMDB=off \
  go install github.com/charmbracelet/freeze@latest
# binary lands in "$(go env GOPATH)/bin/freeze"

GOSUMDB=off is needed when the checksum database (sum.golang.org) is

unreachable and go install hangs on "verifying module ... 504".

If freeze can't be installed, the wrapper automatically falls back to the bundled

scripts/ansi2html.py (stdlib only) + headless Chrome — no extra dependency

beyond a Chrome install. The fallback uses a fixed window size; widen

--window-size in render_ansi.sh if output is clipped.

Bundled scripts

• scripts/render_ansi.sh — render a captured .ansi file to PNG (freeze, else

Chrome fallback). This is the entry point; call it after Step 1.

• scripts/ansi2html.py — stdlib ANSI→HTML converter used by the fallback path.

Handles 24-bit truecolor, 256-color, bold, and resets, preserving background

color blocks (the part naive renderers drop).

Common pitfalls

• Letting the renderer run the command (freeze --execute "delta …") →

degraded output. Capture in a normal shell first, render the file second.

• Non-TTY strips color → force it (--color=always / CLICOLOR_FORCE=1 /

script -q /dev/null).

• Wrong background color → a dark CLI theme rendered on a white page misjudges

contrast. Use the real terminal background.

• Light/dark mismatch → if the terminal is dark, the CLI's colors must be its

dark variant. Verifying a light=true config against a dark terminal shows

inverted, hard-to-read colors (and is itself the bug, not the renderer's fault).

• brew install freeze installs the wrong (GUI cask) tool — use the tap or

go install.