Why JSON.parse Fails on Valid JSON (Hidden Unicode Characters)

Sometimes JSON.parse throws an “Unexpected token” error even when the JSON looks completely valid. This confused me for a long time. Example: const json = '{ "name": "John" }'; JSON.parse(json); Looks correct, right? But sometimes when copying JSON from Slack, Word, Notion, or ChatGPT, hidden Unicode characters are inserted into the string. Common culprits include: • Zero Width Space (U+200B) • Byte Order Mark / BOM (U+FEFF) • Non-breaking space (U+00A0) These characters are invisible, but they break parsers. Example with hidden character: {​ "name": "John" } That tiny invisible character before the quote can cause: Unexpected token in JSON at position X Debugging this is frustrating because the character cannot be seen in most editors. Quick Fix in JavaScript You can remove common hidden characters with: str.replace(/[\u200B-\u200D\uFEFF]/g, "") But first you need to detect them . Tool to Detect Hidden Unicode Characters While debugging this issue I built a small browser tool that hel