Unexpected end of JSON input — causes and fixes

"Unexpected end of JSON input" (or "Unexpected end of data") means the JSON parser hit end-of-file before all open brackets, braces, or quotes were closed. The document is incomplete — truncated somewhere.

The four most common causes

1. Truncated HTTP response

If a streaming connection drops, a read is cancelled early, or the server crashes mid-response, you receive a partial JSON body. The parser reads up to the last byte and then hits EOF with structure still open.

// Axios / fetch may silently give you a partial body
// Always check Content-Length vs actual body length
const res = await fetch(url);
const text = await res.text();
console.log('body length:', text.length);
console.log('last chars:', JSON.stringify(text.slice(-20)));

2. Missing closing bracket or brace

The most common hand-editing mistake — you add a new nested object or array and forget the matching } or ] at the end.

{
  "users": [
    { "id": 1, "name": "Ada" }
  ]
  // ✗ missing closing } for the root object

3. Empty or nearly-empty string

JSON.parse(""), " and ", JSON.parse(" "), " both throw 'Unexpected end of JSON input' because there is no value to parse. Guard before calling parse:

const data = text?.trim() ? JSON.parse(text) : null;

4. Unterminated string

A string that starts with a quote but never closes also produces this error because the parser keeps reading until EOF waiting for the closing quote.

{ "message": "Hello, world   // ✗ no closing quote

How to find the truncation point

• Paste the JSON into the validator — it reports the byte offset of the last valid character before EOF.
• Check text.length against the response's Content-Length header.
• Look at the last ~20 characters: text.slice(-20). If they're mid-value, mid-string, or there are no closing brackets, truncation happened.