Upgrade to PHP 8.5: a staging-first compatibility checklist

Treat an upgrade as a reproducible deployment with a known working runtime available for rollback. Compatibility depends on application code, Composer packages, extensions and encoded commercial software.

Prepare a staging copy

1. Back up files and database together and verify the recovery process.
2. Keep live payments and notifications disabled on staging. Do not expose customer records in a public test copy.
3. Check framework and plugin support for PHP 8.5. Confirm compatible loaders separately for licensed encoded software.
4. Ask the host for a currently patched build and the required modules. Version availability and patch status are different questions.
5. Install locked dependencies and run the application’s tests using the intended web and CLI runtimes.

Test more than the homepage

Check permissions, sessions, forms, uploads, image conversion, email preparation, database writes, APIs and scheduled commands. Review deprecations privately. PHP 8.5 deprecates several explicit resource-close calls; a normal-looking homepage does not prove code compatibility.

Release carefully

Use a quiet period, record both runtime selections and monitor business workflows. Restore the previous supported runtime if compatibility tests fail. Restore data only when the deployment changed it and the recovery plan requires that.

Do not switch every domain together. Marketing websites and billing applications can have different vendor requirements. Remove temporary diagnostics after testing and keep security patches current.