A screenshot contains sharp transitions between text, icons, and flat background colours. Those edges make compression faults more noticeable than they are in many photographs. Use the original screen capture if you have it. A screenshot downloaded from a chat or copied from another post may already have lost the fine strokes you want to preserve.
This page keeps the source dimensions and starts with PNG so you can assess the image without a forced crop. If the capture contains browser chrome, an empty sidebar, or a large irrelevant area, trim it in your editor before processing. A focused capture makes the meaningful text larger when the post is displayed without needing to enlarge the entire file.
Check for account names, email addresses, browser tabs, notifications, and other information you did not intend to publish. This tool does not redact text or blur regions. Make those changes in an editor and inspect the saved image carefully before you select it for a public post.