> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests.md).
# Constraints on Concept Requests
The SNOMED CT International Edition contains some concept hierarchies that have fundamental roles in supporting the design of SNOMED CT. Additions of concepts to these hierarchies may impact the consistency and integrity of SNOMED CT. The following pages set out guidance on the addition of extension concepts within specific hierarchies. In some cases, this guidance may prohibit extensions from adding concepts in a specific hierarchy or at a particular level of a hierarchy. In other cases, the advice is provided on the use case for making particular additions and notes are included on the implications and potential risks arising from such additions.
These constraints are expressed in tables in the following pages, which are arranged to follow the overall hierarchical structure of SNOMED CT.
* [Top Level Concepts and Clinical Concepts](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.1-top-level-concepts-and-clinical-concepts.md)
* [Model Metadata Concept Hierarchies](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.1-core-metadata-hierarchy.md)
* [Core Metadata Hierarchy](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.1-core-metadata-hierarchy.md)
* [Foundation Metadata Concept Hierarchy](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.2-foundation-metadata-concept-hierarchy.md)
* [Linkage Concept Hierarchy](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.3-linkage-concept-hierarchy.md)
* [Namespaces](/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.4-namespaces.md)
Provide Feedback
---
# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.
## 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, and the optional `goal` query parameter:
```
GET https://docs.snomed.org/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests.md?ask=&goal=
```
`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.
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.