Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires shish/phpstan-strict-rules, it could not be found in any version, there may be a typo in the package name. Potential causes: - A typo in the package name - The package is not available in a stable-enough version according to your minimum-stability setting see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details. - It's a private package and you forgot to add a custom repository to find it Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.