What counts as a "line"?
A line is any run of text between two line breaks, including blank ones - pasting a paragraph with gaps between sentences will count those gaps as empty lines too. The separate "non-empty lines" figure ignores lines that are blank or contain only whitespace, which is usually the more genuinely useful number when you're checking something like a list of keywords, URLs, or rows pasted straight from a spreadsheet or CSV file.
Why both counts are shown side by side
Total line count tells you exactly how many line breaks exist in the text block as-is, which matters if you're trying to match a specific line-based format or limit. Non-empty line count strips out the noise of accidental blank lines, giving a cleaner read on how many actual list items, records, or content rows are really there - the two numbers can differ substantially on text pasted from sources that insert extra blank lines between entries.
The word count alongside the line counts
A simple running word count is shown at the same time, calculated by splitting the text on whitespace - useful context when you're checking both the structure (how many lines/items) and the overall length (how many words) of the same pasted text at once, without needing to switch to a separate word-counting tool.
Common uses
Checking how many keywords are in a bulk list before pasting them into another tool with a line limit, verifying a CSV or data export has the expected number of rows, or confirming a list of URLs or email addresses matches an expected count before processing it further.