---
title: "[Set Up Your Project] - Restricted Keywords for UIDs"
description: Restricted keywords to avoid when providing user-defined unique IDs (UIDs) for content types, fields, and taxonomies.
url: https://www.contentstack.com/docs/developers/create-content-types/restricted-keywords-for-uids
product: Contentstack
doc_type: reference
audience:
  - developers
version: unknown
last_updated: 2026-03-25
---

# [Set Up Your Project] - Restricted Keywords for UIDs

This page lists reserved/restricted keywords you must avoid when defining user-defined unique IDs (UIDs) for content types, fields, and taxonomies. It is intended for developers and content modelers setting up or updating a project’s schema, and should be used when naming UIDs to prevent code failures.

## Restricted Keywords for UIDs

When providing user-defined unique IDs (UIDs) for [content type](/docs/developers/create-content-types/about-content-types), [fields](/docs/developers/create-content-types/about-fields/), and [taxonomies](/docs/developers/taxonomy/about-taxonomy), avoid using certain reserved keywords.

**Warning**: Avoid using these keywords as their usage may lead to code failure.

## Restricted keywords for UIDs for Content Type

The following set of keywords cannot be used as the UID of a content type:

- api_key
- built_io_application_user
- built_io_application_user_role
- built_io_audit_log
- built_io_environment
- built_io_extensions
- built_io_installation_data
- built_io_label
- built_io_language
- built_io_publish_queue
- built_io_release
- built_io_upload
- cs_branches
- org_uid
- sys_asset
- sys_metadata

**Note**: Avoid using hyphens (-) in UIDs for content types.

## Restricted keywords for UIDs for Fields

The following set of keywords cannot be used as the UID of a field:

- _exists
- _regex
- *_ids - Fields cannot have UID ending with “_ids.”
- __indexes
- __loc
- __meta
- __v
- _id
- _owner
- _publish_locales
- _shouldFilter
- _shouldLean
- _version
- ACL
- api_key
- app_user_object_uid
- applikation_id
- built_io_upload
- contentstackFilters
- created_at
- created_by
- DEFAULT_ACL
- deleted_at
- dimension
- domain
- embedded_items
- hook
- id
- inbuilt_class
- isApplicationUser
- isNew
- isSystemUser
- klass_id
- locale
- options
- org_uid
- publish_details
- save
- shard_account
- shard_app
- shard_random
- SYS_ACL
- sys_assets
- sys_metadata
- tags
- tags_array
- taxonomies
- tenant_id
- toJSON
- uid
- update
- updated_at
- updated_by

## Restricted Keywords for UIDs for Taxonomies

When creating taxonomies, the following restrictions apply:

- Do **not** use `entries` as the UID for a taxonomy.
- Do **not** use a UID that starts with an underscore (`_`).

## Common questions

### What happens if I use a restricted keyword as a UID?
Using these keywords may lead to code failure.

### Are hyphens allowed in content type UIDs?
**Note**: Avoid using hyphens (-) in UIDs for content types.

### Can a field UID end with `_ids`?
No. `*_ids - Fields cannot have UID ending with “_ids.”`

### Are there special UID rules for taxonomies?
Yes: Do **not** use `entries` as the UID for a taxonomy, and do **not** use a UID that starts with an underscore (`_`).