SyntaxError: Unexpected token ' in JSON at position 0: what it means and how to fix it

What the error means

SyntaxError: Unexpected token ' in JSON at position 0 means the parser expected valid JSON but encountered a character/token that cannot appear there. In practice, it usually means the input is not JSON (or not strict JSON), or it is incomplete.

Most common real-world causes

• You used single quotes for strings or keys. JSON requires double quotes.
• You copied a JavaScript object literal, not strict JSON.
• A templating step produced JSON-like output with single quotes.

Fast debugging steps

• Replace single quotes with double quotes (careful with apostrophes inside text).
• Validate again to catch trailing commas and other non-JSON syntax.
• If the source is JS object literal, serialize with JSON.stringify instead.

Code example (node)

// Not JSON
const bad = "{'a': 1}";

// Strict JSON uses double quotes
const ok = '{"a": 1}';
JSON.parse(ok);

Fix without uploading data

If the JSON contains sensitive data, validate and fix it locally. No Upload Tools runs 100% in your browser.

• JSON Validator to pinpoint the exact syntax error.
• JSON Repair to remove comments/trailing commas when the source is not strict.
• JSON Formatter to pretty-print and inspect structure.
• JSON String Escape if the issue is inside a string (newlines/tabs/quotes).

Workflow: validate -> fix the first error -> validate again -> export/convert.

FAQ

Does the exact token matter? Yes. The token often hints at the root cause: < is usually HTML, u is often undefined, and / often points to comments.

Should I just regex-fix JSON? Avoid blind regex edits. Validate after each change so you know what you fixed and what broke.