python 43 lines · 5 steps

Centralized JSON error handling in Flask

A Flask blueprint that turns exceptions and 404s into consistent JSON error responses.

Explained by highlit

Flask Intermediate error-handling blueprints json-api http-exceptions logging

1import logging
2import traceback
3 
4from flask import Blueprint, jsonify, request
5from werkzeug.exceptions import HTTPException
6 
7log = logging.getLogger(__name__)
8errors = Blueprint("errors", __name__)
9 
10 
11@errors.app_errorhandler(404)
12def handle_not_found(error):
13    response = jsonify(
14        {
15            "error": "not_found",
16            "message": error.description or "The requested resource was not found.",
17            "path": request.path,
18        }
19    )
20    return response, 404
21 
22 
23@errors.app_errorhandler(HTTPException)
24def handle_http_exception(error):
25    return (
26        jsonify({"error": error.name.lower().replace(" ", "_"), "message": error.description}),
27        error.code,
28    )
29 
30 
31@errors.app_errorhandler(500)
32@errors.app_errorhandler(Exception)
33def handle_internal_error(error):
34    log.error("Unhandled exception on %s %s\n%s", request.method, request.path, traceback.format_exc())
35    return (
36        jsonify(
37            {
38                "error": "internal_server_error",
39                "message": "An unexpected error occurred. Please try again later.",
40            }
41        ),
42        500,
43    )

01 / 01

STEP 01

Walkthrough

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Three takeaways

1App-wide error handlers keep every failure response in one predictable JSON shape.
2Handler specificity matters: Flask picks the most specific matching handler, so order broad catch-alls last.
3Log the traceback server-side but return a generic message to clients to avoid leaking internals.

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