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WordPress does not have a built-in setting that limits each post to exactly one category. The Block Editor presents category checkboxes, allowing multiple selections, so you need a plugin, custom server-side enforcement, or an editorial review rule to impose a one-category policy. Choose an approach based on whether it must cover only editor actions or every way a post can be updated.
What “one category” means in WordPress
WordPress permits posts to have one or more categories. In the Block Editor, you assign them from the Categories section of the post settings sidebar, where categories appear as checkboxes. The standard interface therefore does not enforce a one-category limit. See the WordPress post settings sidebar documentation.
Decide whether your rule means exactly one assigned category or no more than one. A site may allow uncategorized drafts, for example, while requiring one category before publication. Those are different policies: a control that limits the selection count may not also require a selection.
Choose an enforcement method
| Approach | What it controls | Best fit | What to verify |
|---|---|---|---|
| Editorial checklist | Reviewers check the saved post; it does not technically restrict other update methods. | Small teams that can reliably check posts before publication. | Who checks drafts and updates, and whether imports or API-written posts are in scope. |
| Plugin | Depends on the plugin. Categories Metabox Enhanced says it adds radio buttons or a dropdown and server-side enforcement. | Sites seeking a no-code option, subject to testing in their own setup. | Current release, compatibility, support activity, required-versus-optional selection, and coverage of every workflow you use. |
| Custom code | Can enforce the rule when terms are saved, if implemented to cover the site’s write paths. | Sites with a development workflow or requirements that a plugin does not meet. | Coverage, testing, maintenance, hierarchy policy, and behavior when categories are deleted. |
Use a plugin for no-code enforcement
The Categories Metabox Enhanced listing says the plugin can replace category controls with radio buttons or a dropdown, configure hierarchical taxonomies independently, and optionally require a selection. It also claims its server-side handler enforces one selected term for Quick Edit, bulk editing, the REST API, WP-CLI, and calls to wp_set_object_terms().
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Those are capabilities stated by the plugin listing, not independently verified compatibility or test results. Before relying on it in production, check its current release and compatibility information on the listing, then test the exact workflows your site uses. Confirm whether it enforces exactly one category or merely prevents multiple selections, and whether it behaves as expected in the Block Editor, any Classic Editor screens, Quick Edit, bulk editing, REST/API updates, WP-CLI, and custom code.
Use custom code only when you can enforce saved terms
Changing checkboxes into radio buttons alters the editing interface, but a user-interface change alone does not guarantee that other routes cannot assign multiple terms. Custom enforcement should apply when category terms are saved and should be tested against the ways content reaches your site, including editor actions, bulk tools, API clients, command-line operations, and programmatic updates.
Plan maintenance alongside implementation: WordPress and plugins change, and code that depends on a particular save path may not cover every workflow. If you cannot maintain and test that coverage, a maintained plugin or a human review process may be more appropriate.
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Use an editorial rule if a technical restriction is unnecessary
A checklist can require the editor or reviewer to inspect the saved post and confirm the intended category before publication. This is a workflow choice, not a built-in WordPress setting; it relies on people following the process and does not constrain imports, API clients, or code-driven updates.
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Categories can be hierarchical
Categories may have parent and child relationships. WordPress says assigning a post to a child category does not require assigning its parent as well. Decide whether “one category” means one assigned term, or whether your editorial policy expects parent terms to be assigned too. These are separate rules. See the WordPress categories screen documentation.
Set a default category deliberately
WordPress has a configurable default category. If a category is deleted, posts assigned to it are reassigned to that default. Choose a sensible default and account for that behavior in your taxonomy maintenance. The categories screen documentation explains category management and defaults.
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Use tags only if they fit your taxonomy
Tags are optional and non-hierarchical, while categories can be hierarchical. A site may use tags for secondary, cross-cutting labels while keeping a single primary category, but that distinction should be clear to editors. See WordPress documentation on categories and tags.
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Do not treat the permalink as proof
A URL containing one category does not show that the post has only one category assigned. WordPress documents that when a post has multiple categories and its permalink uses %category%, one category is selected alphabetically for the URL. Inspect the post’s assigned terms or enforce the rule at save time instead. See the WordPress permalink documentation.
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