Since version 1.1 of Composer there is the composer outdated command. With composer outdated --direct only your direct dependencies are taken into account.
The outdated command shows a list of installed packages that have
updates available, including their current and latest versions. This
is basically an alias for composer show -lo.
The color coding is as such:
green (=): Dependency is in the latest version and is up to date.
yellow (~): Dependency has a new version available that includes backwards compatibility breaks according to semver, so upgrade when you can but it may involve work.
red (!): Dependency has a new version that is semver-compatible and you should upgrade it.
Options
--all (-a): Show all packages, not just outdated (alias for composer show -l).
--direct (-D): Restricts the list of packages to your direct dependencies.
--strict: Returns non-zero exit code if any package is outdated.
--minor-only (-m): Only shows packages that have minor SemVer-compatible updates.
--format (-f): Lets you pick between text (default) or json output format.