Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires builtnorth/coding-standards * -> satisfiable by builtnorth/coding-standards[1.0.0]. - Root composer.json requires wp-cli/wp-cli-tests ^3.0 -> satisfiable by wp-cli/wp-cli-tests[v3.0.0, ..., v3.2.7]. - wp-cli/wp-cli-tests[v3.0.0, ..., v3.0.19] require wp-coding-standards/wpcs ^2.3 -> satisfiable by wp-coding-standards/wpcs[2.3.0]. - wp-cli/wp-cli-tests[v3.1.0, ..., v3.1.3] require wp-cli/wp-cli dev-master as 2.5.1 -> found wp-cli/wp-cli[dev-fix/wp-cli-tests-dep, dev-fix/gracefully-handle-missing-extension, dev-remove/old-global-terms-test, dev-main, dev-add/url-validation, dev-5007-refactor-path-helpers, v0.8.0, ..., v0.25.0, v1.0.0, ..., v1.5.1, v2.0.0, ..., 2.13.x-dev (alias of dev-main)] but it does not match the constraint. Perhaps dev-master was renamed to dev-main? - wp-cli/wp-cli-tests[v3.1.4, ..., v3.2.7] require wp-coding-standards/wpcs ^2.3.0 -> satisfiable by wp-coding-standards/wpcs[2.3.0]. - Conclusion: don't install wp-coding-standards/wpcs 2.3.0 (conflict analysis result)