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

• The input starts with a backslash (often a Windows path) and is not JSON.
• You have invalid escape sequences inside a JSON string.
• A string is double-escaped (you copied a JSON string literal instead of JSON).

Fast debugging steps

• If this is a path/raw text, do not parse it as JSON.
• If this is JSON, validate escapes (\\, \n, \t, \uXXXX).
• If the payload is double-escaped, unescape once before parsing.

Code example (node)

// Example: invalid escapes\nconst bad = '{\"path\": \"C:\\Users\\name\\\"}';\n\n// To embed backslashes, escape them properly\nconst ok = '{\"path\": \"C:\\\\Users\\\\name\\\\\"}';\nJSON.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.