JSONDecodeError: Extra data and multiple JSON values

What the error means

The parser completed one JSON value and then found another non-whitespace character. A single JSON document contains one top-level value. Two adjacent objects, an NDJSON stream or a log suffix cannot be loaded as one document with json.loads or JSON.parse. First identify the format; wrapping unrelated text in an array is not a general fix.

Exact messages by runtime

Messages depend on the input and runtime version. Node and Python rows were reproduced locally. Other rows cite official documentation or source. Rows marked as fragments or templates preserve the source wording and are not complete exception transcripts. Browsers and libraries may append location details.

Causes you can reproduce

import json
json.loads('{} {}')

const text = '{"id":1}\n{"id":2}';
JSON.parse(text);

import json
json.loads('{"ok":true}\nrequest finished')

How to fix it

1. Inspect the first unexpected character after the completed value. Determine whether it begins another JSON value or is an unrelated suffix.
2. For one-document APIs and files, fix the producer to return one value, often an array of records.
3. For documented NDJSON, parse each record line separately. Do not split pretty-printed multiline JSON into lines.
4. For other streams of JSON values, use a streaming decoder and consume every value. Do not discard the suffix after the first successful parse.

const text = '{"id":1}\n{"id":2}\n';
const records = text.split(/\r?\n/)
  .filter(line => line.trim() !== '')
  .map(line => JSON.parse(line));
// One ordinary document instead:
const document = JSON.stringify(records);

import json
with open('records.ndjson', encoding='utf-8') as stream:
    for number, line in enumerate(stream, 1):
        if not line.strip():
            continue
        try:
            record = json.loads(line)
        except json.JSONDecodeError as error:
            raise ValueError(f'Invalid record on line {number}') from error
        print(record)

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "strings"
)

func main() {
    dec := json.NewDecoder(strings.NewReader("{} {}"))
    for {
        var value any
        err := dec.Decode(&value)
        if err == io.EOF { break }
        if err != nil { panic(err) }
        fmt.Println(value)
    }
}

Find the exact position with Tool Kumar

1. Copy the exact input text, including its original whitespace. For HTTP failures, copy the raw response body.
2. Open the Tool Kumar JSON validator and paste the text. The document stays in your browser.
3. Read the line and column in the error or fixable-issue banner. For an invalid document, select Go to error to move the caret to that location.
4. Inspect the preceding token as well as the marked character. A parser marks where it discovered the problem; the missing quote, separator or value can start earlier.

Python character offsets are zero-based, while its displayed lines and columns are one-based. V8 string positions count UTF-16 code units; Go offsets count bytes read. Unicode text can make these offsets differ. Use the original text and its line/column context rather than copying an offset between runtimes.

Tool Kumar can classify some input as fixable loose JSON. Review a proposed change before using the repair action, then validate the result against your API contract. For empty input, inspect the producer or response because there is no character to select.

Frequently asked questions

Related errors and tools

• JSON trailing comma errors in objects and arrays
• Unexpected end of JSON input: empty or truncated data
• Bad control character in string literal in JSON
• All JSON error guides
• JSON syntax reference
• Convert an array of JSON records to CSV

Standards and diagnostic sources

RFC 8259 and ECMA-404 define JSON syntax. Diagnostic wording belongs to the parser. The table links each cited message to its source.

• MDN JSON.parse error reference
• Python json documentation and JSONDecodeError attributes
• Go encoding/json documentation
• WebKit source for the JSON Parse error prefix