> ## Documentation Index
> Fetch the complete documentation index at: https://docs.permutive.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Requests & Responses

> Sending & receiving calls from the API

The Permutive API follows [REST](https://en.wikipedia.org/wiki/REST)ful principles. It is designed to have predictable, resource-oriented URLs and make use of built-in HTTP features such as HTTP response codes and HTTP authentication.

## Base URL

The base URL for the Permutive API is

```
https://api.permutive.app/
```

<Note>Customers who have been with Permutive longer may have deployments with a base URL of `https://api.permutive.com`. Permutive continues to support this address but we recommend and ask that new deployments use the `.app` base URL.</Note>

## Content types

All data exchanged between clients and the API is **JSON**, including errors, so all API requests should set the `Content-Type` header to `application/json`.

## Field types

Unless otherwise stated, these are the default data types for common categories of fields:

| Field type         | Format                                                                                |
| ------------------ | ------------------------------------------------------------------------------------- |
| Resource IDs       | Version 4 [UUID](https://en.wikipedia.org/wiki/Universally_unique_identifier) format. |
| Permutive User IDs | Version 4 [UUID](https://en.wikipedia.org/wiki/Universally_unique_identifier) format. |
| Session & view IDs | Version 4 [UUID](https://en.wikipedia.org/wiki/Universally_unique_identifier) format. |
| Timestamps         | Requested & returned in [ISO8601](https://en.wikipedia.org/wiki/ISO_8601) format.     |

## Error responses

Please see [Errors](./errors) to understand what error types may be included in responses.