flask flask.cli.NoAppException raised when .env/.flaskenv

The Fix

Upgrade to version 2.0.0 or later.

Based on closed pallets/flask issue #3561 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -27,6 +27,9 @@ Unreleased
 -   When specifying a factory function with ``FLASK_APP``, keyword
     argument can be passed. :issue:`3553`
+-   When loading a ``.env`` or ``.flaskenv`` file on top level directory,
+    Flask will not change current work directory to the location of dotenv
+    files, in order to prevent potential confusion. :pr:`3560`

repro.py

# app.py
from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, Flask!'

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 2.0.0 or later.\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n

Why This Fix Works in Production

Trigger: Error: Could not locate a Flask application. You did not provide the "FLASK_APP" environment variable, and a "wsgi.py" or "app.py" module was not found in the…
Mechanism: Prevent Flask from changing the current working directory when loading .env or .flaskenv files from the top-level directory, which caused NoAppException errors.
Why the fix works: Prevent Flask from changing the current working directory when loading .env or .flaskenv files from the top-level directory, which caused NoAppException errors. (first fixed release: 2.0.0).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Surfaces as: Error: Could not locate a Flask application. You did not provide the "FLASK_APP" environment variable, and a "wsgi.py" or "app.py" module was not found in the current directory.

Proof / Evidence

GitHub issue: #3561
Fix PR: https://github.com/pallets/flask/pull/3560
First fixed release: 2.0.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.63

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Also reported in #3535, which I closed for a larger discussion in https://github.com/pallets/flask/issues/3108#issuecomment-608550814. I'm not opposed to it, would be good to hear from @jab.”

@davidism · 2020-04-07 · source

“Sorry for the delay and thank you for the ping, @davidism. Responded in https://github.com/pallets/flask/pull/3560#issuecomment-612948226.”

@jab · 2020-04-13 · source

Failure Signature (Search String)

Error: Could not locate a Flask application. You did not provide the "FLASK_APP" environment variable, and a "wsgi.py" or "app.py" module was not found in the current directory.

Error Message

Stack trace

error.txt

Error Message
-------------
Error: Could not locate a Flask application. You did not provide the "FLASK_APP" environment variable, and a "wsgi.py" or "app.py" module was not found in the current directory.

Minimal Reproduction

repro.py

# app.py
from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, Flask!'

What Broke

Executing 'flask run' results in NoAppException due to incorrect working directory.

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 2.0.0 or later.

When NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pallets/flask/pull/3560

First fixed release: 2.0.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use if it changes public behavior or if the failure cannot be reproduced.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
2.0.0	Fixed

Related Issues

No related fixes found.

Cluster: flask:configuration-error All hubs All clusters

Related clusters: Data consistency Other Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

flask flask.cli.NoAppException raised when .env/.flaskenv exists in parent directory and (Fix)