What it does
Paste the exact message Android showed — such as “App not installed as package conflicts with an existing package” or an INSTALL_FAILED_… code from adb — and the decoder returns the most likely cause and the fix. It covers signature conflicts, downgrades, corrupt files, incompatible Android versions, storage, Play Protect and unknown-sources prompts.
The four causes behind most failures
- Signature conflict — a version signed with another key is installed. Uninstall it.
- Downgrade — the version code is not higher than the installed one.
- Damaged file — re-download from the original link.
- Storage — free some space.
All messages, with explanations: APK install errors reference.
Preventing them as a developer
- Sign every version with the same key; back the key up.
- Raise the version code on every build you share.
- Share a direct https link rather than forwarding the file through chat apps.
- Tell testers to uninstall builds from other tools before installing yours.
Frequently asked questions
Why does Android just say 'App not installed'?
It is a generic message. Most often an existing app with the same package name was signed with a different key.
Can I install an older version over a newer one?
Not directly. Uninstall the newer version first, which deletes the app's local data.