---
title: Introduction
description: The two hosts, what an Application is, and the first call every integration makes.
---

The Hydda One API is plain HTTPS with JSON bodies. Every request carries an access token.

## Two hosts

| Host | What it serves |
| --- | --- |
| `https://idp.hydda.one` | The token endpoint, OpenID discovery, the signing keys and the operational contexts list. |
| `https://api.hydda.one` | Every other route, under `/v1/booking`, `/v1/billing`, `/v1/crm` and `/v1/integrations`. |

The development environment uses `idp.dev.hydda.one` and `api.dev.hydda.one`. Credentials from one environment do not work in the other.

## Who calls the API

Two kinds of client call the API.

- **An Application** belongs to one organization. An administrator of that organization creates it and gives you its `client_id` and a client secret. It gets a token with the `client_credentials` grant.
- **An installed connector** is an app an organization installs, such as an ERP or e-signing connector. It signs in with its own private key and gets a token for one installation.

Both get a short-lived access token from the token endpoint. See [Authentication](/guides/authentication).

## What a token can reach

A token belongs to one organization. An administrator grants it roles, and each role holds in part of the organization. Hydda One calls those parts **operational contexts**: the organization itself, a property or a co-working business, for example.

Start every integration by listing the operational contexts the token can act in, with `GET /v1/operational-contexts` on the identity host. Most other routes take an `operationalContextId` from that list. [Roles](/guides/roles) lists which role opens which routes.

## Conventions

- Bodies are JSON, sent with `Content-Type: application/json`.
- Ids are UUIDs.
- Times are ISO 8601 in UTC. Dates without a time are `YYYY-MM-DD`.
- Money is an integer amount in minor units, with an ISO 4217 currency. `12500` in `SEK` is 125.00 kronor.
- A list that can grow returns a `nextCursor`. Pass it as `cursor` to read the next page.
- Every failure returns a problem details body with a machine-readable `code`. See [Errors](/guides/errors).