Quick answer
# starts a comment.
robots.txt Comments
# starts a comment. Comment only from # to end of line.
Common causes
- # in wrong place.
- Comment breaking directive.
How to fix
- Use # for full-line comment.
- No inline comment in spec.
FAQ
- Comment in robots?
- # to EOL.
- Inline?
- Not standard.
Fix it now
Try in validator (prefill this example)