SWR OpenAPI

Comprehensive guide for using swr-openapi — type-safe SWR bindings for OpenAPI schemas via openapi-fetch and openapi-typescript.

When to Apply

Reference these guidelines when:

• Writing React components that fetch data from an OpenAPI-defined API
• Setting up type-safe data fetching with SWR and OpenAPI schemas
• Implementing pagination with useInfinite
• Managing cache revalidation and mutation with useMutate
• Refactoring existing SWR or fetch code to use swr-openapi

Installation

npm i swr-openapi openapi-fetch
npm i -D openapi-typescript typescript

Enable noUncheckedIndexedAccess in tsconfig.json for enhanced type safety.

Schema Generation

Generate TypeScript types from your OpenAPI schema:

npx openapi-typescript ./path/to/api/v1.yaml -o ./src/lib/api/v1.d.ts

This produces a paths type export used to type the client and all hooks.

Setup — Creating Hooks

Create a client with openapi-fetch, then use hook builders to export typed hooks. Each builder takes a client and a prefix string. The prefix ensures SWR avoids cache collisions between different APIs.

import createClient from "openapi-fetch";
import {
  createQueryHook,
  createImmutableHook,
  createInfiniteHook,
  createMutateHook,
} from "swr-openapi";
import { isMatch } from "lodash-es"; // recommended compare function
import type { paths } from "./my-openapi-3-schema"; // generated types

const client = createClient<paths>({
  baseUrl: "https://myapi.dev/v1/",
});

const prefix = "my-api";

export const useQuery = createQueryHook(client, prefix);
export const useImmutable = createImmutableHook(client, prefix);
export const useInfinite = createInfiniteHook(client, prefix);
export const useMutate = createMutateHook(client, prefix, isMatch);

Hook Builder Signatures

createQueryHook(client, prefix)       // → useQuery
createImmutableHook(client, prefix)   // → useImmutable
createInfiniteHook(client, prefix)    // → useInfinite
createMutateHook(client, prefix, compare) // → useMutate

• client — An openapi-fetch client instance.
• prefix — A unique string per client. Used only for SWR cache key uniqueness, not included in actual requests.
• compare — (createMutateHook only) A CompareFn (init: any, partialInit: any) => boolean for matching cache keys during mutation. Lodash isMatch is recommended.

Hook API Reference

useQuery

Type-safe wrapper over useSWR. Fetches data via client.GET().

const { data, error, isLoading, isValidating, mutate } = useQuery(
  path,
  init,
  config,
);

Parameters:

• path — Any endpoint that supports GET requests (type-checked against schema).
• init — Fetch options for the endpoint (params, headers, etc.), or null to skip the request (conditional fetching).
• config — (optional) SWR configuration options.

Returns: An SWR response (data, error, isLoading, isValidating, mutate).

How it works internally:

function useQuery(path, ...[init, config]) {
  return useSWR(
    init !== null ? [prefix, path, init] : null,
    async ([_prefix, path, init]) => {
      const res = await client.GET(path, init);
      if (res.error) {
        throw res.error;
      }
      return res.data;
    },
    config,
  );
}

Example:

import { useQuery } from "./my-api";

function BlogPost({ postId }: { postId: string }) {
  const { data, error, isLoading } = useQuery("/blogposts/{post_id}", {
    params: {
      path: { post_id: postId },
    },
  });

  if (isLoading || !data) return "Loading...";
  if (error) return `An error occurred: ${error.message}`;
  return <div>{data.title}</div>;
}

Conditional fetching (pass null as init to skip):

const { data } = useQuery(
  "/blogposts/{post_id}",
  postId ? { params: { path: { post_id: postId } } } : null,
);

useImmutable

Identical API to useQuery, but wraps useSWRImmutable — disables automatic revalidations. Use for data that doesn't change.

const { data, error, isLoading, isValidating, mutate } = useImmutable(
  path,
  init,
  config,
);

Parameters and return values are the same as useQuery.

useInfinite

Type-safe wrapper over useSWRInfinite for paginated data.

const { data, error, isLoading, isValidating, mutate, size, setSize } =
  useInfinite(path, getInit, config);

Parameters:

• path — Any endpoint supporting GET requests.
• getInit — (pageIndex: number, previousPageData?: ResponseData) => FetchOptions | null — Returns fetch options for each page, or null to stop loading.
• config — (optional) SWR infinite options.

Returns: An SWR infinite response (data, error, isLoading, isValidating, mutate, size, setSize).

Limit/Offset pagination:

useInfinite("/something", (pageIndex, previousPageData) => {
  // Stop if no more data
  if (previousPageData && !previousPageData.hasMore) return null;
  // First page
  if (!previousPageData) return { params: { query: { limit: 10 } } };
  // Subsequent pages
  return { params: { query: { limit: 10, offset: 10 * pageIndex } } };
});

Cursor-based pagination:

useInfinite("/something", (pageIndex, previousPageData) => {
  if (previousPageData && !previousPageData.nextCursor) return null;
  if (!previousPageData) return { params: { query: { limit: 10 } } };
  return {
    params: { query: { limit: 10, cursor: previousPageData.nextCursor } },
  };
});

useMutate

Type-safe wrapper around SWR's global mutate. Updates and revalidates the client-side cache for specific endpoints.

const mutate = useMutate();

await mutate([path, init], data, options);

Parameters:

• path — Any endpoint supporting GET requests.
• init — (optional) Partial fetch options to narrow which cache entries to match.
• data — (optional) Data to update the cache, or an async function for remote mutation.
• options — (optional) SWR mutate options.

Returns: A promise containing an array where each item is updated data for a matched key or undefined.

Example — revalidate all entries for a path:

const mutate = useMutate();

// Revalidate all /blogposts cache entries
await mutate(["/blogposts"]);

Example — revalidate a specific entry:

// Revalidate a specific blog post
await mutate(["/blogposts/{post_id}", { params: { path: { post_id: "123" } } }]);

Example — optimistic update:

await mutate(
  ["/blogposts/{post_id}", { params: { path: { post_id: "123" } } }],
  { ...currentData, title: "Updated Title" },
  { revalidate: false },
);

Key Patterns

File Organization

src/
  lib/
    api/
      v1.d.ts          # Generated types (do not edit)
      client.ts         # Client + hook exports
  components/
    MyComponent.tsx     # Uses hooks from client.ts

Multiple API Clients

Use distinct prefixes for each API to avoid cache collisions:

const clientA = createClient<pathsA>({ baseUrl: "https://api-a.dev/v1/" });
const clientB = createClient<pathsB>({ baseUrl: "https://api-b.dev/v1/" });

export const useQueryA = createQueryHook(clientA, "api-a");
export const useQueryB = createQueryHook(clientB, "api-b");

Error Handling

Errors thrown by swr-openapi are the error property from the openapi-fetch response. The shape matches the error schemas defined in your OpenAPI spec:

const { data, error } = useQuery("/endpoint", { /* ... */ });

if (error) {
  // error is typed according to the endpoint's error response schema
  console.error(error);
}

Conditional Fetching

Pass null as init to prevent the request from firing:

const { data } = useQuery(
  "/users/{id}",
  userId ? { params: { path: { id: userId } } } : null,
);

SWR Cache Key Structure

swr-openapi uses a tuple [prefix, path, init] as the SWR cache key. Understanding this is important for debugging and for useMutate:

• prefix — The unique string passed to the hook builder
• path — The OpenAPI path string (e.g., "/blogposts/{post_id}")
• init — The fetch options object (params, headers, etc.)

When init is null, the key becomes null and SWR skips the request.

Init Parameter Structure

The init object mirrors openapi-fetch's request options:

{
  params: {
    path: { post_id: "123" },      // URL path parameters
    query: { limit: 10, offset: 0 }, // Query string parameters
    header: { "X-Custom": "value" }, // Request headers
    cookie: { session: "abc" },      // Cookies
  },
  body: { title: "New Post" },       // Request body (for non-GET)
}

For GET endpoints, only params is typically used since GET requests don't have a body.

Optional Init

If an endpoint has no required parameters, init can be omitted entirely:

// Endpoint with no required params — init is optional
const { data } = useQuery("/blogposts");

// Equivalent to:
const { data } = useQuery("/blogposts", {});

// With SWR config but no params:
const { data } = useQuery("/blogposts", {}, { refreshInterval: 5000 });

Exported Types

The library exports utility types for extracting request/response types from your schema:

import type { TypesForGetRequest, TypesForRequest, CompareFn } from "swr-openapi";
import type { paths } from "./my-schema";

// Extract types for a specific GET endpoint
type BlogPostTypes = TypesForGetRequest<paths, "/blogposts/{post_id}">;

type Data = BlogPostTypes["Data"];       // Response data type
type Error = BlogPostTypes["Error"];     // Error response type
type Init = BlogPostTypes["Init"];       // Full init/options type
type Path = BlogPostTypes["Path"];       // Path parameters type
type Query = BlogPostTypes["Query"];     // Query parameters type
type Headers = BlogPostTypes["Headers"]; // Header parameters type

TypesForRequest is the generic version that accepts any HTTP method:

import type { TypesForRequest } from "swr-openapi";

type PostTypes = TypesForRequest<paths, "post", "/blogposts">;