Logging configuration in FastAPI

Introduction

Logging helps you see what your FastAPI app is doing. It records messages about events, errors, and info so you can understand and fix problems.

You want to track errors in your FastAPI app to fix bugs.

You need to monitor app activity to understand user behavior.

You want to save important events for later review.

You want to debug your app during development.

You want to keep a record of requests and responses.

Syntax

FastAPI

import logging

logging.basicConfig(level=logging.LEVEL, format='FORMAT')

logger = logging.getLogger('your_logger_name')

logger.LEVEL('Your message')

Replace LEVEL with logging levels like DEBUG, INFO, WARNING, ERROR, or CRITICAL.

The format controls how the log message looks, including time, level, and message.

Examples

This sets the log level to INFO and prints messages like INFO:App started.

FastAPI

import logging

logging.basicConfig(level=logging.INFO, format='%(levelname)s:%(message)s')
logger = logging.getLogger('app')
logger.info('App started')

This shows detailed logs with time, level, and message, useful for debugging.

FastAPI

import logging

logging.basicConfig(level=logging.DEBUG, format='%(asctime)s - %(levelname)s - %(message)s')
logger = logging.getLogger('app')
logger.debug('Debugging info')

Sample Program

This FastAPI app logs an info message every time the root endpoint is called.

FastAPI

import logging
from fastapi import FastAPI

logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
logger = logging.getLogger('fastapi_app')

app = FastAPI()

@app.get('/')
async def root():
    logger.info('Root endpoint was called')
    return {'message': 'Hello World'}

Important Notes

Use different log levels to control what messages appear.

You can configure logging to write to files instead of the console.

Logging helps you find problems faster than print statements.

Summary

Logging records important events in your FastAPI app.

Use logging.basicConfig to set up logging format and level.

Call logger methods like info() or debug() to write messages.