Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires infection/infection ^0.29.0 -> satisfiable by infection/infection[0.29.0, ..., 0.29.10]. - Root composer.json requires vimeo/psalm ^5.17.0 -> satisfiable by vimeo/psalm[5.17.0, ..., 5.26.1]. - infection/infection[0.29.0, ..., 0.29.8] require infection/mutator ^0.4 -> satisfiable by infection/mutator[0.4.0]. - infection/infection 0.29.10 requires php ^8.2 -> your php version (8.1.31) does not satisfy that requirement. - infection/infection 0.29.9 requires thecodingmachine/safe dev-master as 2.5.0 -> found thecodingmachine/safe[dev-master] but it does not match your minimum-stability. - Conclusion: don't install infection/mutator 0.4.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.