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Python Verified by running the parser on CPython 3.14.3.

Extra data: line L column C (char N)

json.loads parsed a complete value and then found more content. Python calls that extra data. If the reported line is 2 or later and each line looks like a complete record, the file is JSON Lines and needs to be read one line at a time.

Paste your JSON and see exactly where it breaks

Input

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What actually causes it

Ranked by how often each one turns out to be the answer.

  1. 01 The file is JSON Lines

    One JSON object per line, no commas, no wrapping array. Standard output format for logs, BigQuery exports and streaming APIs.

    Breaks

    with open('events.jsonl') as f:
    data = json.load(f)   # Extra data: line 2 column 1

    Works

    with open('events.jsonl') as f:
    data = [json.loads(line) for line in f if line.strip()]

# or, with pandas
import pandas as pd
df = pd.read_json('events.jsonl', lines=True)

  2. 02 json.dumps was called in a loop, appending to one file

    Each call writes a complete document, so the file ends up holding several. Either write JSON Lines deliberately and read it as such, or collect the records into a list and dump once.

    Breaks

    for row in rows:
    f.write(json.dumps(row))

    Works

    for row in rows:
    f.write(json.dumps(row) + '\n')   # NDJSON, read line by line

# or
f.write(json.dumps(rows))              # one array

  3. 03 Two responses concatenated

    A retry appended to a buffer rather than replacing it.

The same mistake in other runtimes

The underlying problem is identical; only the wording differs. If a colleague reports one of these, they are looking at the same thing you are.

JavaScript (V8) Unexpected non-whitespace character after JSON at position 8 (line 2 column 1)

Questions

Is there a Python function that reads several documents from one string?
json.JSONDecoder().raw_decode(s, idx) parses one value and tells you where it stopped, so you can loop. For line-delimited files, splitting on newlines is simpler and much faster.
Why does the char offset not match my line and column?
char is the absolute index into the string, while line and column are the human-readable position. They describe the same point.

Fix it now

Paste the payload into the tool above, or go straight to the one built for this job.

Convert JSON Lines to an array