# Environment variables
Source: https://www.inngest.com/docs/reference/python/overview/env-vars

You can use environment variables to control some configuration.

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## `INNGEST_API_BASE_URL`

Origin for the Inngest API. Your app registers itself with this API.

- Defaults to `https://api.inngest.com/`.
- Can be overwritten by specifying `api_base_url` when calling a `serve` function.

You likely won't need to set this.

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## `INNGEST_DEV`

- Set to `1` to disable [production mode](/docs/reference/python/overview/prod-mode).
- Set to a URL if the Dev Server is not hosted at `http://localhost:8288`. For example, you may need to set it to `http://host.docker.internal:8288` when running the Dev Server within a Docker container (learn more in our [Docker guide](/docs/guides/development-with-docker)). Please note that URLs are not supported below version `0.4.6`.

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## `INNGEST_ENV`

Use this to tell Inngest which [branch environment](/docs/platform/environments#branch-environments) you want to send and receive events from.

Can be overwritten by manually specifying `env` on the Inngest client.

This is detected and set automatically for some platforms, but others will need manual action. See our [configuring branch environments](/docs/platform/environments#configuring-branch-environments) guide to check if you need this.

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## `INNGEST_EVENT_API_BASE_URL`

Origin for the Inngest Event API. The Inngest client sends events to this API.

- Defaults to `https://inn.gs/`.
- If set, it should be an origin (protocol, host, and optional port). For example, `http://localhost:8288` or `https://my.tunnel.com` are both valid.
- Can be overwritten by specifying `base_url` when creating the Inngest client.

You likely won't need to set this. But some use cases include:
- Forcing a production build of your app to use the Inngest Dev Server instead of Inngest Cloud for local integration testing. You might want `http://localhost:8288` for that.
- Using the Dev Server within a Docker container. You might want `http://host.docker.internal:8288` for that. Learn more in our [Docker guide](/docs/guides/development-with-docker).

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## `INNGEST_EVENT_KEY`

The secret key used to send events to Inngest.

- Can be overwritten by specifying `event_key` when creating the Inngest client.
- Not needed when using the Dev Server.

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## `INNGEST_SIGNING_KEY`

The secret key used to sign requests to and from Inngest, mitigating the risk of man-in-the-middle attacks.

- Can be overwritten by specifying `signing_key` when calling a `serve` function.
- Not needed when using the Dev Server.

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## `INNGEST_SIGNING_KEY_FALLBACK`

Only used during signing key rotation. When it's specified, the SDK will automatically retry signing key auth failures with the fallback key.

Available in version `0.3.9` and above.