screenshot.notes - kubed-io/selenium-flow GitHub Wiki

Reach for extract first. An image of text costs orders of magnitude more than the text, cannot be quoted, and may be a picture of a half-rendered page. Screenshot when the appearance is the answer — layout, styling, a chart that only exists once rendered.

bytes is the blank-capture check. A capture of a page that never painted still returns a valid PNG; it is just small. Comparing bytes against a floor of a couple of thousand catches that, and is far more reliable than checking a particular expected size — a full-page capture of a mostly-white page is only about 10KB, so a tight threshold goes flaky on a rendering difference.

width/height leave the window resized. They are a resize, not a capture option, and everything afterwards sees the new size. full_page is different: it grows the window to the document height for the capture and puts it back.

Whether the caller can see it depends on the client. MCP returns a real image content block, and Claude Code and Claude Desktop render it. Several clients do not, and n8n's agent cannot see one at all — the base64 rides along in the tool message costing ~18k tokens for nothing. When a person will look at the result, give them the saved file's url — it opens in any browser and needs no bearer token, and it is signed and time-limited when the server has a token to sign with. Screenshots are kept by default, on any page, so the link is normally there; save=false opts out, and a server with no DATA_DIR returns file_error and the image instead.