# Identifiers and URLs

All objects in the API have an `id` field indicating their logical identifier.

| Parameter | Type | Description |
|  --- | --- | --- |
| id | `string` | Identifies the object within the API. The `id` field will not be larger than 128 characters (in SQL it corresponds to a `varchar(128)`). |


> ❗️ IDs are not globally unique
With the exception of `workspace_id`, all `id` fields are only unique within a given workspace. In your datastore, you should always store the `workspace_id` along with an `id` field to ensure uniqueness.


These fields must always be treated as opaque strings - no guarantees are made about the internal structure of the `id` fields for an object.

The `id` field is always defined by the API server and is guaranteed to be unique relative to the `type` field within a given workspace - this means no two user objects will have the same `id` field, but a user and a company may have the same value for their `id` fields. Some object types (such as Contact), also support client defined identifiers.

The company and user objects deserve special mention when it comes to identity for two reasons -

* They allow you send your own *external identifiers*
* The contact `id` field is in some cases, aliased to `intercom_user_id`. This is done to distinguish it from other identifiers in the API and to avoid confusion as to which object type an `id` denotes.