JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Check what the API sent back

Most of the time, this error comes from an API call. Print the status code and the start of the body before you parse it:

response = requests.get(url, timeout=10)
print(response.status_code, response.headers.get("Content-Type"))
print(repr(response.text[:200]))

What you see usually points straight at the cause:

• '', an empty body. The server answered without any content, as with a 204 No Content response, or with an error it didn’t bother to describe.
• '<!DOCTYPE html>…', a web page. You got a 404 from a wrong URL, a login page because your token is missing or expired, a 403 from a firewall, or a 502 from a proxy. More on why servers send HTML.
• Plain text, such as Internal Server Error. The server crashed and sent its error message as text.

In every one of these cases, the fix is in the request, not the JSON. Once you’ve sorted it, it’s worth making your code fail with a clearer message next time:

response = requests.get(url, timeout=10)
response.raise_for_status()

if "application/json" not in response.headers.get("Content-Type", ""):
    raise ValueError(f"Expected JSON, got: {response.text[:200]!r}")

data = response.json()

Reading a JSON file

When the JSON comes from a file, the usual reason is that Python is reading nothing. If you’ve already called f.read(), the file is at its end, so a second json.load(f) gets an empty string. Parse the text you already read, or call f.seek(0) first. Also check how you opened the file: open(path, "w") empties it straight away, so open it with "r" to read it.

Another common slip is passing the file name to json.loads(). It parses the string you give it, so json.loads("settings.json") tries to read the letters settings.json as JSON and fails at char 0. Open the file and use json.load(f), without the s, which reads the file for you.

Files that start with a byte order mark

Some Windows programs save UTF-8 files with an invisible byte order mark at the start. Python then fails at char 0 with a slightly different message, Unexpected UTF-8 BOM (decode using utf-8-sig). The message already tells you the fix: open the file with the utf-8-sig encoding, which works whether or not the mark is there.

with open("settings.json", encoding="utf-8-sig") as f:
    settings = json.load(f)

When the error is further into the text

If the line or column isn’t 1, you do have JSON, but one value in it is broken. Python expected a value at that spot, and found something else. For example, {"a": ,} fails at column 7, where the value is missing. The usual suspects:

• A missing value, as in "owner": ,
• A string in single quotes, such as 'active'
• A trailing comma in an array, such as [1, 2,]
• True, False, or None. These mean the data was written with str() or print() instead of json.dumps().

The fixer above repairs all of these. In a large file, you can also print the text around error.pos to see exactly what Python tripped over:

try:
    data = json.loads(text)
except json.JSONDecodeError as error:
    print(f"line {error.lineno}, column {error.colno}")
    print(text[max(0, error.pos - 40):error.pos + 40])

The same error elsewhere