In JIRA 6.x, 7.x, or 8.x,9.x it is possible to rename a project key. However, it is not possible to reuse a project key that was previously used in Jira.

Even archiving a Project, Jira will still keep the history of already used keys.

Current Behavior:

• Let's say the user has renamed a project key from "ABC" to "KLM"
• Although there is no project that uses the project key ABC, the user is not allowed to re-use "ABC" for the new project key.

Suggested behavior:

• Ideally, user should be able to re-use the project key "ABC" for other/new project

Workaround

• Currently, there is no workaround to re-use a project key.

Additional note: If business allow, you can delete the project holding the old-key, it will allow to reuse any key that is in use.

DO NOT use SQL queries to change DB tables to try to re-use keys.

This will lead to database inconsistencies as projects are connected to issues, attachments, permissions, workflows, plugins, custom scripts, and etc..