How can I see which spaces, tabs and hidden characters are in my text before I clean it?

What each mark means

• · a middle dot: an ordinary space.
• → an arrow: a tab, with the tab itself kept after it so its width still shows.
• ⍽: a non-breaking space (NBSP).
• ␣: another special Unicode space, such as a thin space.
• ¶: the end of a line.
• [ZWSP], [WJ], [BOM], [ZWNJ] and [ZWJ]: zero-width characters, each by name.

Example: a line that looks normal

That tells you which rules you need: the non-breaking space is handled by the special-spaces rule, on by default; the tab needs tab conversion turned on; and the zero-width space needs the zero-width rule turned on.

Steps

1. Open the Whitespace cleaner and paste your text.
2. To see the original exactly as it is, untick every rule for now and set blank lines to 'Keep them as they are', so the preview shows the text with no cleaning.
3. Turn on 'Show invisible characters in the preview' and read the marks.
4. Turn the rules you need back on; the preview shows the result with the same marks, so you can confirm what you wanted gone is gone.

Do the marks end up in the copied text?

No. The marks are drawn in the preview box only. 'Copy result', the download button and 'Apply to input' all use the real cleaned text without marks. So you can leave the option on the whole time without worrying.

Where the diagnosis helps

• A trailing space shows as a dot just before ¶, a common reason two lines that look identical are not.
• A line that looks empty but holds dots, meaning it contains only spaces.
• If you see ␍ before ¶, the text arrived with Windows line breaks the browser did not convert, and the line-ending rule deals with them.

What the marks do not show: direction marks such as RLM get no mark, and the tool does not remove them anyway. Arabic diacritics and the tatweel are not this tool's business either.