# contains only ### Description With `contains only`, you check that the list on the left only contains values from the list, which could be a taxonomy, on the right. ### Example ``` p is Person p.selected_services contains only free_services ``` You have a [taxonomy](/guides/glossary/taxonomy.md) defined, which lists all the free services your organization offers to clients. When onboarding new clients, you want to check whether the clients have only selected the free services or if you need to charged them for additional paid services. The expression in the example will only evaluate to true if a client has only selected free services, and false if one or more paid services have been chosen. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.atfinity.io/rule-language/operators/list-operators/contains-only.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.