Unexpected end of JSON input: an empty or cut-off body

The parser ran out of text before the JSON was complete. Either there was no text at all (an empty response body), or the text stops part-way through, like a download cut off in the middle.

What each runtime prints

We ran these inputs through JSON.parse in each browser and Node version, and through json.loads in Python. These are the messages exactly as printed.

(empty string)

{"items": [1, 2

• Only an empty body gives "Unexpected end of JSON input" in Chrome and Node 20+. Cut-off JSON gets a more specific message there, such as "Expected ',' or ']' after array element", which points at the column where the text stops.
• Node 18 says "Unexpected end of JSON input" for both, so on Node 18 you cannot tell an empty body from a cut-off one.
• Python reports an empty body as "Expecting value: line 1 column 1 (char 0)", the same message it gives for an HTML page.

Common causes

1. 1

   A 204 No Content or a HEAD request

   Many APIs answer DELETE and some PUT requests with 204 and no body. Calling res.json() on it throws.

2. 2

   An error with no body

   A 401, 403 or 500 from some servers and gateways has no body at all. The code calls res.json() before checking res.ok.

3. 3

   A response cut off by a timeout or a size limit

   A proxy timeout, a dropped connection, or a body size limit ends the response early. The JSON stops mid-value.

4. 4

   A stream read too early

   Parsing the first chunk of a streamed response, or a file that another process is still writing.

5. 5

   A database column or log line that was too short

   JSON saved into a VARCHAR(255) column, or a log system that cuts long lines, keeps only the start of the document.

How to fix it

Read the body as text first. An empty string is a normal answer for some requests; handle it before parsing.

JavaScript

const res = await fetch(url, { method: 'DELETE' });
if (!res.ok) throw new Error(`${res.status} from ${res.url}`);
const text = await res.text();
const data = text ? JSON.parse(text) : null; // 204 and empty bodies give null

Python

r = requests.delete(url, timeout=10)
r.raise_for_status()
data = r.json() if r.content else None  # 204 and empty bodies give None

• If the text is not empty but stops early, compare its length with the Content-Length header. A shorter body means the connection or a proxy cut it off.
• The JSON Repair tool can close cut-off JSON so you can read what arrived, but the last value may be incomplete. Fix the source rather than shipping repaired data.

Related

• Unexpected token '<': your code got an HTML page, not JSON
• Trailing comma in JSON: "Expected double-quoted property name"
• JSON Repair
• JSON Validator