Python JSON Logger

4.0.0 verified Tue May 12 auth: no python install: verified quickstart: verified

A JSON log formatter for the Python logging package that supports various JSON encoders. Current version is 4.0.0, with regular releases typically made every few months.

pip install python-json-logger

Common errors

error ModuleNotFoundError: No module named 'json_log_formatter' ↓

cause The `python-json-logger` package, which provides the `json_log_formatter` module, is not installed in the current Python environment.

fix

pip install python-json-logger

error ModuleNotFoundError: No module named 'python_json_logger' ↓

cause Although the package is named `python-json-logger`, the main module containing the `JsonFormatter` class is `json_log_formatter`.

fix

from json_log_formatter import JsonFormatter

error ImportError: cannot import name 'JsonLogger' from 'json_log_formatter' ↓

cause The class name `JsonLogger` is incorrect; the correct class for JSON formatting in this library is `JsonFormatter`.

fix

from json_log_formatter import JsonFormatter

error TypeError: Object of type <ClassName> is not JSON serializable ↓

cause A log record contains an object (e.g., datetime, custom class instance) that the default JSON encoder cannot serialize, and no custom `json_default` function or `json_encoder` class was provided to `JsonFormatter`.

fix

Configure JsonFormatter with a json_default function to convert non-serializable objects into a serializable format:

import datetime
from json_log_formatter import JsonFormatter

def custom_serializer(o):
    if isinstance(o, datetime.datetime):
        return o.isoformat()
    raise TypeError(f"Object of type {o.__class__.__name__} is not JSON serializable")

formatter = JsonFormatter(json_default=custom_serializer)

error TypeError: JsonFormatter.__init__() got an unexpected keyword argument 'some_arg' ↓

cause An unrecognized or misspelled keyword argument was passed to the `JsonFormatter` constructor.

fix

Refer to the library's documentation for the correct list of supported arguments for JsonFormatter, such as json_default, json_encoder, json_message_key, json_extra, etc.

Warnings

breaking The use of some older imports has changed, e.g., 'from pythonjsonlogger.jsonlogger import jsonlogger' is incorrect. ↓

fix Migrate to 'from pythonjsonlogger.jsonlogger import JsonFormatter'.

gotcha Ensure that required fields are correctly specified in comma-separated format to avoid formatting issues. ↓

fix Use the new formatter syntax that supports comma-separated lists.

Install compatibility verified last tested: 2026-05-12

python os / libc status wheel install import disk

3.10 alpine (musl) - - 0.07s 17.9M

3.10 slim (glibc) - - 0.04s 18M

3.11 alpine (musl) - - 0.11s 19.7M

3.11 slim (glibc) - - 0.10s 20M

3.12 alpine (musl) - - 0.09s 11.6M

3.12 slim (glibc) - - 0.09s 12M

3.13 alpine (musl) - - 0.08s 11.2M

3.13 slim (glibc) - - 0.11s 12M

3.9 alpine (musl) - - 0.07s 17.7M

3.9 slim (glibc) - - 0.06s 18M

Imports

JsonFormatter
```
from pythonjsonlogger.jsonlogger import JsonFormatter
```
Make sure to use the full path for compatibility.

Quickstart verified last tested: 2026-04-23

Basic usage of JsonFormatter to log messages in JSON format.

import logging
from pythonjsonlogger.jsonlogger import JsonFormatter

logger = logging.getLogger('my_logger')
handler = logging.StreamHandler()
formatter = JsonFormatter()
handler.setFormatter(formatter)
logger.addHandler(handler)
logger.setLevel(logging.INFO)
logger.info('This is a log message with JSON formatting')