JSON
- SyntaxError: Unexpected token in JSON — what it means and how to fix it
- SyntaxError: Unexpected end of JSON input — causes and fixes
- Unexpected token u in JSON at position 0: "undefined" is not valid JSON
- Unexpected token '<', "<!DOCTYPE "... is not valid JSON
- Trailing comma in JSON: "Expected double-quoted property name"
- SyntaxError: Expected property name or '}' in JSON
- Single quotes are not valid in JSON — use double quotes
- Bad control character in string literal in JSON
- Bad escaped character in JSON (Python: Invalid \escape)
- Duplicate keys in JSON: why they parse, and why they are a bug
- NaN and Infinity are not valid JSON
- Why big numbers in JSON change their last digits
- JSON fails at position 0 because of a byte-order mark (BOM)
- Comments are not allowed in JSON
- True, False and None are not JSON: Unexpected token 'T' or 'N'
- Unexpected non-whitespace character after JSON at position N
- json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
- JSONDecodeError: Expecting property name enclosed in double quotes
- Missing comma in JSON: Expected ',' or '}' after property value
JavaScript / JSX
YAML
- YAML error: tabs are not allowed for indentation
- YAML error: mapping values are not allowed here (in this context)
- YAML error: did not find expected key (or could not find expected ':')
- YAML error: duplicated mapping key
- The Norway problem: why YAML turns NO, yes and off into booleans
- YAML error: did not find expected '-' indicator
- YAML error: found character that cannot start any token
- YAML alias bombs: "excessive aliasing" and the billion laughs attack
XML
- XML mismatched tag: opening and ending tag mismatch
- ParseError: not well-formed (invalid token)
- XML error: Entity 'nbsp' not defined (undefined entity)
- XML error: junk after document element (extra content at the end)
- Unescaped & in XML: xmlParseEntityRef: no name
- SAXParseException: Content is not allowed in prolog