Plain-English answers to the deployment errors developers hit most often — written so you can fix the problem in your own project, with or without DeployDoc.
Why your app works locally but crashes after deploy — and how to find every missing key.
Decode “Environment Variable not found”, missing NEXT_PUBLIC_ prefixes, and per-environment scoping.
Diagnose Netlify build failures caused by env scope, branch deploys, and contexts.
Why Railway marks your app unhealthy and how to bind to process.env.PORT correctly.
Service env vs environment groups, service URL drift, and runtime mismatches on Render.
nodejs_compat flag, Buffer / fs limits, and why certain npm packages crash on Workers.
Fix the site URL, redirect allow-list, and preview-domain wildcards in Supabase Auth.
Permission errors after enabling RLS, missing GRANTs, and the policy patterns that actually work.
Raw-body parsing, per-environment webhook secrets, and the three common signature pitfalls.
Allow-list preview and production callbacks without breaking local development.
Scan compiled JS for secret prefixes and stop NEXT_PUBLIC_ / VITE_ leaks before they ship.
Diff two diagnosis reports to confirm what's fixed, what regressed, and what's still failing.