OpenAPI to Fetch Client

What this tool does

Paste an OpenAPI 3.x or Swagger 2.0 document and this tool generates a single TypeScript file: a dependency-free client that calls your API with fetch. It focuses on the operations layer (paths): function names, path parameters, query parameters, header parameters, request bodies, response types, and the small runtime helpers needed to call fetch safely.

Use it when you already have, or plan to generate, schema types from components.schemas separately. Local $ref schema names become imported TypeScript types from your types_module; blank types_module emits placeholder aliases so the output still compiles while you wire real types in later.

It can generate:

• exported async functions or one client class;
• operation names from operationId or method + path;
• single request-object calls or positional path/body arguments;
• ApiError throwing or { data, error, response } result unions;
• base URLs from the spec or from an override;
• typed path, query, header, body, and response references;
• JSDoc from summaries/descriptions and @deprecated markers.

Worked example

Use a spec like this:

{"openapi":"3.1.0","servers":[{"url":"https://api.example.com"}],"paths":{"/pets/{petId}":{"get":{"operationId":"getPet","parameters":[{"name":"petId","in":"path","required":true,"schema":{"type":"string"}},{"name":"include","in":"query","schema":{"type":"string"}}],"responses":{"200":{"description":"OK","content":{"application/json":{"schema":{"$ref":"#/components/schemas/Pet"}}}}}}}}}

With the default functions, request object, and throw ApiError settings, the output contains a call shaped like:

export interface GetPetRequest {
  petId: string;
  include?: string;
}

export async function getPet(params: GetPetRequest, options: RequestOptions = {}): Promise<Pet> {
  return apiFetch("GET", `/pets/${encodeURIComponent(String(params.petId))}`, { include: params.include }, {}, undefined, options);
}

Point types_module at your generated schema declarations (for example ./types) so local refs such as #/components/schemas/Pet are imported as Pet. Use base_url when you want the generated file to call staging, production, or a test server regardless of the spec's servers section.

Limits and edge cases

• This generates one text file, not a multi-file SDK package. It does not create models/, apis/, npm metadata, or a runtime library folder.
• It reads paths operations only. It does not generate schema model declarations from components.schemas; use a schema-types generator for that and import those types with types_module.
• Only local refs such as #/components/schemas/Pet or #/definitions/Pet become named TypeScript types. External or remote refs fall back to unknown because this tool does not fetch the network.
• application/json request/response bodies are preferred; otherwise the first declared content type is used. Form-data and cookie parameters are noted in comments but are not automatically assembled.
• The success type comes from the lowest 2xx response (then default). Other response shapes are runtime unknown in the thrown ApiError or result union.
• Auth helpers, retries, middleware, interceptors, and date revivers are intentionally left to RequestOptions.headers, RequestOptions.fetch, or your surrounding app code.

FAQ