OpenApiGen

OpenApiGen is a .NET tool that generates simple, type-safe TypeScript clients from OpenAPI definitions. The generated clients are designed for easy integration with Axios and React Query.

Usage

Run the tool with:

openapigen <configuration-file> <openapi-file> <output-dir>

• <configuration-file>: Path to the configuration JSON file
• <openapi-file>: Path to the OpenAPI definition JSON file
• <output-dir>: Output directory for the generated TypeScript client (will be purged)

For help:

openapigen --help

Note on Any Types

This tool implements a workaround for a bug in Microsoft.Extensions.ApiDescription.Server 9.0.8, where nullable types are incorrectly emitted as type "any" in the OpenAPI definition. The generator heuristically locates an equivalent non-nullable schema and applies the intended nullability. This assumes the base, non-nullable schema is emitted correctly.

Example Output

Sample TypeScript code generated for a PATCH operation on /User/{id}:

// === patch /User/{id} === export type UserIdPatchRequest = { firstName: null | string lastName: null | string } export type UserIdPatch200Response = { firstName: string lastName: string } export type UserIdPatch400Response = ProblemDetails export type UserIdPatch404Response = ProblemDetails export async function patchUserIdAsync(axios: AxiosInstance, bearer: string, id: string, request: UserIdPatchRequest): Promise<[200, UserIdPatch200Response] | [400, UserIdPatch400Response] | [404, UserIdPatch404Response]> { const resp = await axios.patch(`/User/${id}`, request, { validateStatus: () => true, headers: { Authorization: `Bearer ${bearer}` } }) switch (resp.status) { case 200: return [200, resp.data as UserIdPatch200Response] case 400: return [400, resp.data as UserIdPatch400Response] case 404: return [404, resp.data as UserIdPatch404Response] default: throw `Unexpected status ${resp.status}` } }

Features

• Generates TypeScript clients from OpenAPI definitions
• Designed for easy integration with Axios and React Query
• Inlines types for clarity and simplicity
• Support for Bearer token (authorization header) and ApiKey (cookie)
• Minimal dependencies, no runtime bloat

Note on Nullable Types

This tool implements a workaround for a bug in Microsoft.Extensions.ApiDescription.Server 9.0.8, where nullable types are incorrectly emitted as type "any" in the OpenAPI definition. The generator heuristically locates an equivalent non-nullable schema (with the same required members) and applies the intended nullability. This assumes the base, non-nullable schema is emitted correctly.