Where curly quotes are the right choice
Any text a human reads as prose — articles, books, marketing copy, documentation — should use curly quotes. Typographers distinguish opening marks from closing marks, and this distinction is part of what makes typeset text look considered rather than typed. If you're writing in Word or Google Docs with default settings, you're already getting this automatically.
Where straight quotes are required, not optional
Code of any kind. A programming language's string literal syntax specifically requires the straight " or ' character — a curly quote pasted into code is a syntax error, not a style choice. This is the single most common way curly quotes cause real damage: copying a snippet from a blog post or Word document that auto-curled the quotes, pasting it into an editor, and getting an error that doesn't obviously point to your quotes as the culprit.
URLs and file paths. Some systems tolerate a curly quote inside a URL by encoding it; many silently break instead — assume URLs need straight characters throughout.
CSV and structured data files. If a field is quoted using " as the CSV escape character, a curly quote inside the data is just content, while an unescaped straight quote can break parsing.
Search queries. Typing a curly quote into a search box when the indexed content uses straight quotes (or vice versa) can silently return fewer or zero results, because many search implementations treat them as different characters during literal matching.
How to tell which one you're looking at
At most font sizes the visual difference is subtle. If you suspect a mismatch, paste the character into our Unicode inspector: a straight double quote is U+0022, a curly opening double quote is U+201C, a curly closing double quote is U+201D. Same logic for single quotes/apostrophes at U+0027 versus U+2018/U+2019. If your keyboard is typing the wrong quotes entirely, see our quotation marks wrong troubleshooting guide.
The practical rule
Write prose with smart quotes on — no one should turn it off for general writing. But before pasting anything into code, a URL, a CSV, or a search box, either retype the quotes manually or run the text through a plain-text paste — see our Word-to-website encoding guide for the same Ctrl+Shift+V technique, or convert quotes in bulk using our Text Cleaner.