What to do if you get an error when uploading a feed?

RSS feed errors are their own category because a feed is machine-read: a single stray character invalidates the whole file. Yandex’s reference explains why and gives a fixing procedure per error.

Why feeds break

A feed must satisfy strict requirements — data format, mandatory fields, limits on string and URL length, XML encoding and syntax. Yandex names the small things that kill a file: an extra quotation mark, a wrong date format, an over-long URL.

The parsing errors

• Malformed attributes — values must be quoted, quotes must match, attributes must not overlap or nest wrongly, special characters must be escaped (& rather than a bare ampersand), and no element may repeat an attribute name.
• Missing quotation mark — every opening quote needs its closing one. Yandex’s practical hint: if the file was hand-edited, look at what changed last.
• Incorrectly redefined HTTP header — duplicated or wrongly set headers in the feed.
• Improperly closed CDATA — each section runs from <![CDATA[ to ]]>, and a stray ] inside can close it early. That is the subtle one, because the file looks correct and the parser disagrees.
• Invalid character — a character outside the range the format permits.

The working method Yandex prescribes

1. Find the error code.
2. Read what it means.
3. Follow the steps.
4. Fix all reported errors the same way.
5. Submit for re-check.
6. Apply the prevention advice so it does not recur.

The recurring instruction worth generalising

Nearly every entry ends with the same two suggestions: run the file through an XML or YML validator, and if the feed is generated programmatically, check the code that generates it. That is the real fix. A feed corrected by hand breaks again on the next publish; a generator corrected once stops producing the fault.