Why Your JSON Looked Fine But Failed to Parse
JSON that looks visually correct but fails to parse is often caused by "smart quotes" (curly quotation marks introduced by a word processor, which aren't valid JSON quote characters), invisible characters copied in from another source, or a subtle trailing comma — none of which are easy to spot by eye but are immediately flagged by a strict parser.
These specific issues are frustrating precisely because they're genuinely difficult to catch by visual inspection alone.
Smart quotes from a word processor
Text copied from a word processor or certain note-taking apps often has "smart quotes" — curly opening and closing quotation marks — automatically substituted for straight quotes. These look nearly identical to standard quotes at a glance but aren't valid JSON syntax, which strictly requires straight double quotes.
Invisible or non-standard characters
Text copied from certain sources can carry invisible characters (like a non-breaking space or a byte-order-mark) that aren't visible in most text editors but are treated as unexpected characters by a strict JSON parser, causing a failure at a position that looks, visually, like nothing is wrong.
How to catch these specific issues
Pasting the JSON into a validator that reports an exact error position (rather than just "invalid JSON") and checking that exact character is the most reliable way to catch these subtle issues — for smart quotes specifically, retyping the quotes directly rather than pasting from a word processor avoids the problem at the source.