Checklists for software errors, setup, and tool workflows.

1. Reproduce

2. Isolate

3. Apply

4. Verify

Latest checklists

If you see an error like fatal: Unable to create 'path/to/repo/.git/index.lock': Fi...

Fix Cloudflare Error 521 After a Server Update
If you see Cloudflare error 521 after updating your server, the origin web server is refusing the...

Python Virtual Environment Not Activating on Mac: Fixes
You open Terminal, run source venv/bin/activate, and nothing happens—or you get an e...

Fixing NGINX Upstream Connection Refused SSL Errors
When NGINX logs upstream connection refused for an SSL backend, it usually means the...

Docker Compose ENV Not Passed to Entrypoint: Fix
You define an environment variable in your docker-compose.yml, but when the containe...

Fix Firefox Secure Connection Failed After Update
After a Firefox update, you might see a "Secure Connection Failed" error when visiting we...