# Gatsby quickstart

## 1. Install `hypertune`

Once you have a Gatsby application ready, install Hypertune's JavaScript SDK:

{% tabs %}
{% tab title="npm" %}

```bash
npm install hypertune
```

{% endtab %}

{% tab title="yarn" %}

```bash
yarn add hypertune
```

{% endtab %}

{% tab title="pnpm" %}

```bash
pnpm add hypertune
```

{% endtab %}
{% endtabs %}

## 2. Set environment variables

Define the following environment variables in your `.env.development` and `.env.production` files:

{% code title=".env.production" %}

```bash
GATSBY_HYPERTUNE_TOKEN=token
HYPERTUNE_FRAMEWORK=gatsby
HYPERTUNE_OUTPUT_DIRECTORY_PATH=src/generated
```

{% endcode %}

Replace `token` with your main project token which you can find in the Settings tab of your project.

## 3. Update `gatsby-config.ts`

Update your `gatsby-config.ts` to load the environment variables with `dotenv`:

{% code title="gatsby-config.ts" %}

```tsx
import type { GatsbyConfig } from 'gatsby'

// Load environment variables
require('dotenv').config({
  path: `.env.${process.env.NODE_ENV}`,
})

const config: GatsbyConfig = {
  siteMetadata: {
    title: `Hypertune Gatsby Demo`,
    siteUrl: `https://www.yourdomain.tld`,
  },
  graphqlTypegen: true,
  plugins: [],
}

export default config
```

{% endcode %}

## 4. Update `.babelrc`

First install the `babel-preset-gatsby` package as a devDependency:

{% tabs %}
{% tab title="npm" %}

```bash
npm install -D babel-preset-gatsby
```

{% endtab %}

{% tab title="yarn" %}

```bash
yarn add -D babel-preset-gatsby
```

{% endtab %}

{% tab title="pnpm" %}

```bash
pnpm add -D babel-preset-gatsby
```

{% endtab %}
{% endtabs %}

Then create a `.babelrc` at the root of your project:

{% code title=".babelrc" %}

```json
{
  "presets": [
    [
      "babel-preset-gatsby",
      {
        "targets": {
          "browsers": [">0.25%", "not dead"]
        },
        "exclude": ["@babel/plugin-transform-classes"]
      }
    ]
  ]
}
```

{% endcode %}

## 5. Generate the client

Generate a type-safe client to access your flags by running:

{% tabs %}
{% tab title="npm" %}

```bash
npx hypertune
```

{% endtab %}

{% tab title="yarn" %}

```bash
yarn hypertune
```

{% endtab %}

{% tab title="pnpm" %}

```bash
pnpm hypertune
```

{% endtab %}
{% endtabs %}

## 6. Use the client

Add a new file called `getHypertune.ts` that creates and exports a `getHypertune` function:

{% code title="lib/getHypertune.ts" %}

```typescript
import { createSourceForServerOnly } from '../generated/hypertune'

const hypertuneSource = createSourceForServerOnly({
  token: process.env.GATSBY_HYPERTUNE_TOKEN!,
})

export default async function getHypertune() {
  await hypertuneSource.initIfNeeded() // Check for flag updates

  return hypertuneSource.root({
    args: {
      context: {
        environment:
          process.env.NODE_ENV === 'development'
            ? 'development'
            : 'production',
        user: {
          id: 'e23cc9a8-0287-40aa-8500-6802df91e56a',
          name: 'Example User',
          email: 'user@example.com',
        },
      },
    },
  })
}
```

{% endcode %}

{% tabs %}
{% tab title="Server-side Rendering" %}
To access flags in `getServerData` during Server-side Rendering (SSR), use the `getHypertune` function:

{% code title="src/pages/ssr.tsx" %}

```tsx
import { GetServerData } from 'gatsby'
import * as React from 'react'
import getHypertune from '../lib/getHypertune'

type ServerData = { exampleFlag: boolean }

export const getServerData: GetServerData<
  ServerData
> = async () => {
  const hypertune = await getHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  return { props: { exampleFlag } }
}

export default function Page({
  serverData,
}: {
  serverData: ServerData
}) {
  return <div>Example Flag: {serverData.exampleFlag}</div>
}
```

{% endcode %}
{% endtab %}

{% tab title="Client-side Rendering" %}
To access flags in the browser during Client-side Rendering (CSR), first create a new `<AppHypertuneProvider>` component that wraps the generated `<HypertuneProvider>` component:

{% code title="components/AppHypertuneProvider.tsx" %}

```tsx
import * as React from 'react'
import { HypertuneProvider } from '../generated/hypertune.react'

export default function AppHypertuneProvider({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <HypertuneProvider
      createSourceOptions={{
        token: process.env.GATSBY_HYPERTUNE_TOKEN!,
      }}
      rootArgs={{
        context: {
          environment:
            process.env.NODE_ENV === 'development'
              ? 'development'
              : 'production',
          user: {
            id: 'e23cc9a8-0287-40aa-8500-6802df91e56a',
            name: 'Example User',
            email: 'user@example.com',
          },
        },
      }}
    >
      {children}
    </HypertuneProvider>
  )
}
```

{% endcode %}

Then wrap your app with the `<AppHypertuneProvider>` component in both `gatsby-browser.tsx` and `gatsby-ssr.tsx`:

{% code title="gatsby-ssr.tsx" %}

```tsx
import * as React from 'react'
import AppHypertuneProvider from './src/components/AppHypertuneProvider'
import type { GatsbyBrowser } from 'gatsby'

export const wrapRootElement: GatsbyBrowser['wrapRootElement'] =
  ({ element }) => {
    return <AppHypertuneProvider>{element}</AppHypertuneProvider>
  }
```

{% endcode %}

Then use the generated `useHypertune` hook:

{% code title="src/components/ClientComponent.tsx" %}

```tsx
import * as React from 'react'
import { useHypertune } from '../generated/hypertune.react'

export default function ClientComponent() {
  const hypertune = useHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  return <div>Example Flag: {String(exampleFlag)}</div>
}
```

{% endcode %}

If you access a flag immediately after your app loads, you'll get your hardcoded fallback value if the SDK hasn't initialized from [Hypertune Edge](/concepts/hypertune-edge.md) yet. This can result in layout shift or a flicker if the flag value changes when the SDK initializes.

To avoid this, wrap your page with the generated `<HypertuneHydrator>` and `<HypertuneRootProvider>` components, passing them `dehydratedState` and `rootArgs` from the server:

{% code title="src/pages/csr.tsx" %}

```tsx
import { GetServerData } from 'gatsby'
import * as React from 'react'
import ClientComponent from '../components/ClientComponent'
import {
  DehydratedState,
  RootArgs,
} from '../generated/hypertune'
import {
  HypertuneHydrator,
  HypertuneRootProvider,
} from '../generated/hypertune.react'
import getHypertune from '../lib/getHypertune'

type ServerData = {
  dehydratedState: DehydratedState | null
  rootArgs: RootArgs
}

export const getServerData: GetServerData<
  ServerData
> = async () => {
  const hypertune = await getHypertune()

  const dehydratedState = hypertune.dehydrate()
  const rootArgs = hypertune.getRootArgs()

  return {
    props: { dehydratedState, rootArgs },
  }
}

export default function Page({
  serverData,
}: {
  serverData: ServerData
}) {
  const { dehydratedState, rootArgs } = serverData

  return (
    <HypertuneHydrator dehydratedState={dehydratedState}>
      <HypertuneRootProvider rootArgs={rootArgs}>
        <ClientComponent />
      </HypertuneRootProvider>
    </HypertuneHydrator>
  )
}
```

{% endcode %}

If you have a Content Security Policy, add the following to your `connect-src` directive: `https://edge.hypertune.com https://gcp.fasthorse.workers.dev`. This enables reporting of flag evaluations, experiment exposures, and analytics events.
{% endtab %}

{% tab title="Functions" %}
To access flags in Gatsby Functions, use the `getHypertune` function:

{% code title="src/api/hello.ts" %}

```typescript
import {
  GatsbyFunctionRequest,
  GatsbyFunctionResponse,
} from 'gatsby'
import getHypertune from '../lib/getHypertune'

export default async function handler(
  req: GatsbyFunctionRequest,
  res: GatsbyFunctionResponse
) {
  const hypertune = await getHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  res.send({ exampleFlag })
}
```

{% endcode %}
{% endtab %}
{% endtabs %}

## 7. (Optional) Add the Hypertune Toolbar

The Hypertune Toolbar lets you view and override feature flags directly in your frontend. [Follow the guide](/sdk-reference/hypertune-toolbar.md) to add it to your app.

## 8. (Optional) Include a build-time snapshot

To improve reliability, you can include a snapshot of your flag logic in the generated client at build time. The SDK will instantly initialize from the snapshot first before fetching the latest flag logic from [Hypertune Edge](/concepts/hypertune-edge.md).

Add the following environment variable to your `.env` file:

```bash
HYPERTUNE_INCLUDE_INIT_DATA=true
```

Then regenerate the client.

You can keep the snapshot fresh by setting up a [webhook](/integrations/webhooks.md) to regenerate the client on every Hypertune commit. In this case, you don't need to initialize from Hypertune Edge at all, eliminating network latency and bandwidth, improving both performance and efficiency.

## Next steps

Now you can update the logic for `exampleFlag` from the Hypertune UI without updating your code or waiting for a new build, deployment, or app release.

To add a new flag, create it in the Hypertune UI then regenerate the client.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.hypertune.com/getting-started/gatsby-quickstart.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.