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updatedAt: 2026-07-23T08:09:54.000Z
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Fetch the complete documentation index at: https://docs.apollo.io/llms.txt. Use this file to discover all available pages before exploring further.

# Authentication

How you authenticate to the Apollo API depends on who is making the request. Apollo users use an API key, and partners building on behalf of mutual users use OAuth 2.0. To see how the API, MCP, and CLI compare, check [Build with Apollo](https://docs.apollo.io/docs/build-with-apollo).

## Apollo API (Apollo users)

**For Apollo users**: You need to create an API key to access the Apollo API. Pass the key in the `x-api-key` header of every request.

The [Create API Keys](https://docs.apollo.io/docs/create-api-key) article details how to create a new key and ensure that it is ready to use. Some endpoints, such as [Get a List of Users](https://docs.apollo.io/docs/get-a-list-of-users), are only accessible with a [master key](https://docs.apollo.io/docs/create-api-key), which grants access to all endpoints.

The following example passes an API key in the `x-api-key` header to call the `auth/health` endpoint:

```bash
curl --request GET \
  --url 'https://api.apollo.io/api/v1/auth/health' \
  --header 'Content-Type: application/json' \
  --header 'Cache-Control: no-cache' \
  --header 'x-api-key: YOUR_API_KEY'
```

## OAuth 2.0 (Partners)

**For Apollo partners**: To make API requests on behalf of an Apollo user, you need to implement the [OAuth 2.0 authorization flow](https://docs.apollo.io/docs/use-oauth-20-authorization-flow-to-access-apollo-user-information-partners).

If you'd like to promote an integration you've built to Apollo's APIs, you may [submit an application](https://docs.apollo.io/docs/add-your-integration-to-apollos-marketplace) to have the integration feature on Apollo’s Marketplace.