---
title: Customize reference generation | Stainless
description: Generate API reference content without using the Stainless API.
---

To describe interfaces across each SDK language and raw HTTP, Stainless uses a custom file format called SDKJSON. The SDKJSON file contains method signatures, types, request/response examples, and more for your API and each of your SDKs.

An SDKJSON is generated from your OpenAPI spec and your Stainless config.

Stainless Docs allows you to define a custom SDKJSON loader function in your Astro config file. This function overrides the framework’s default behavior of fetching your OpenAPI + Stainless config from the Stainless API and generating SDKJSONs behind the scenes.

The simplest way to take advantage of this API is to use `fileSystemSDKJSONLoader` which reads an OpenAPI spec and Stainless config from the file system and generates SDKJSON files.

## Using local OpenAPI and Stainless config files

Using `fileSystemSDKJSONLoader` completely sidesteps the Stainless API, meaning you do not need an internet connection or Stainless API key to generate API reference documentation.

astro.config.ts

```
import { defineConfig } from 'astro/config';
import { stainlessDocs } from '@stainless-api/docs';
import { fileSystemSDKJSONLoader } from '@stainless-api/docs';


export default defineConfig({
  integrations: [
    stainlessDocs({
      title: 'My Docs',
      apiReference: {
        stainlessProject: 'my-docs',
        loadSDKJSONFiles: fileSystemSDKJSONLoader({
          specPath: '<path_to_openapi.json>',
          configFilePath: '<path_to_stainless.yml>',
          languages: ['http', 'typescript', 'python'],
        }),
      },
    }),
  ],
});
```

## Advanced usage

### Overriding the SDKJSON generation process

You can also optionally override the `generateSDKJSON` function to further customize the SDKJSON generation process.

astro.config.ts

```
import { defineConfig } from 'astro/config';
import { stainlessDocs } from '@stainless-api/docs';
import { fileSystemSDKJSONLoader } from '@stainless-api/docs';


export default defineConfig({
  integrations: [
    stainlessDocs({
      title: 'My Docs',
      apiReference: {
        stainlessProject: 'my-docs',
        loadSDKJSONFiles: fileSystemSDKJSONLoader({
          specPath: '<path_to_openapi.json>',
          configFilePath: '<path_to_stainless.yml>',
          languages: ['http', 'typescript', 'python'],
          generateSDKJSON: async ({ spec, config, stainlessProject, language }) => {
            const result = await myCustomSDKJSONGenerationFunction({
              spec,
              config,
              stainlessProject,
              language,
            });
            return result;
          },
        }),
      },
    }),
  ],
});
```

### Writing you own loader function

You can also write your own loader function to completely control the SDKJSON generation process. This is more involved than using the `fileSystemSDKJSONLoader`, but gives you ultimate control over from where you load your OpenAPI spec and Stainless config, and how you generate the SDKJSONs for each language.

astro.config.ts

```
import { defineConfig } from 'astro/config';
import { stainlessDocs } from '@stainless-api/docs';
import { writeFile } from 'node:fs/promises';
import path from 'node:path';


export default defineConfig({
  integrations: [
    stainlessDocs({
      title: 'My Docs',
      apiReference: {
        stainlessProject: 'my-docs',
        loadSDKJSONFiles: async ({ createCodegenDir }) => {
          const spec = await fetch('https://example.com/openapi.json').then((r) => r.text());
          const config = await fetch('https://example.com/stainless.yml').then((r) => r.text());
          const result = await myCustomSDKJSONGenerationFunction({
            spec,
            config,
            language: 'typescript',
          });
          const codegenDir = createCodegenDir();
          const sdkJsonFilePath = path.join(codegenDir.pathname, 'sdk.json');
          await writeFile(sdkJsonFilePath, result);
          return [
            {
              path: sdkJsonFilePath,
              languages: ['typescript'],
            },
          ];
        },
      },
    }),
  ],
});
```