To install the PHP_CodeSniffer Plugin follow these steps:
1. From the menu bar select Help -> Install New Software ...
2. Click the Add Site... button.
3. Enter a name like "PTI Update Site" into the Name field or leave it empty to retrieve it from the update site. Enter http://www.phpsrc.org/eclipse/pti/ into the Location field. Click OK.
4. Back in the Install Dialog, you should see the PHP Tool Integration category. Expand it and select your desired feature. Click Next >.
5. Review the features that you are about to install. Click Next.
6. Accept the terms of the agreement and click Finish.
7. If prompted, click to restart the Eclipse workbench.