Postman2CSharp

Writing C# API clients by hand from a Postman collection is tedious in a specific, grinding way. You look at an endpoint, manually create the request type, figure out the response shape, deal with the auth header, handle the case where the API returns different shapes for 200 vs 400, repeat for every endpoint. It is not hard, just relentless. I could not find a free tool that did it well, so I built one.

What actually runs in your browser

The tool takes a Postman collection JSON and generates a complete, organized C# project: interfaces, concrete client implementations, all request and response types, zero external dependencies. The whole thing runs in the browser via Blazor WebAssembly. No data leaves the user's machine, which matters when the Postman collection contains internal API credentials or proprietary endpoint shapes.

Configuration is deep: JSON serializer (STJ or Newtonsoft), nullability handling, how to handle multiple response types (OneOf or object), error handling strategy, retry logic, cancellation token support. You download a zip you can drop straight into your project.

The hard parts

API requests have enormous variation. Path params, query params, JSON bodies, XML bodies, form data, multiple response status codes, different auth types, inline schemas vs. referenced schemas. Getting the generator to handle every combination correctly required extensive edge case testing. The trickiest part was class deduplication: two different endpoints that send structurally identical payloads should share one C# class. Figuring out when two JSON schemas are "the same" across different endpoints is not trivial, especially when the schemas are inferred from example request bodies rather than defined formally.

WASM bundle size was also a real constraint. All .NET DLLs ship to the client by default, and a Blazor WASM app can balloon to 20-30MB fast. I implemented page-level lazy loading so only the DLLs needed for the current page get downloaded on navigation. Initial load went from painful to reasonable.

Still running without me

Over 8,000 total users, more than 2,000 API clients generated, 3,000+ downloads. 70 users per week with no active marketing. The tool does what it says and developers find it. I consider that the cleanest success metric.