Picking the right HTTP client library is one of those decisions that looks trivial during a sprint planning session and comes back to haunt teams months later - when you're scaling to hundreds of microservices, onboarding junior developers, or debugging a production outage at 2 AM. In ASP.NET Core, developers typically face three serious contenders: the built-in HttpClient with IHttpClientFactory, RestSharp, and Refit. Each has a distinct philosophy, trade-off profile, and sweet spot. This guide gives your team the full picture - so you can make a decision that holds up in production, not just in a prototype.
HTTP client choice quietly shapes your resilience and testability. The full comparison setup is on Patreon, ready to run.
The Three Contenders: What They Are and Why They Exist
Before diving into trade-offs, it helps to understand why each option exists and what problem it was originally solving.
HttpClient / IHttpClientFactory is the built-in .NET mechanism for making HTTP requests. HttpClient itself has existed since .NET 4.5, but for years it was famously misused - teams instantiated it per-request, exhausting socket connections. IHttpClientFactory, introduced in ASP.NET Core 2.1, solved the socket exhaustion problem by managing the lifetime of HttpMessageHandler instances through a pool. Today, IHttpClientFactory with typed clients is Microsoft's recommended baseline for HTTP communication in .NET applications. It ships with the framework, requires no additional packages, and integrates natively with dependency injection, resilience policies (Polly / Microsoft.Extensions.Http.Resilience), and distributed tracing.
RestSharp is the oldest of the three, predating .NET Core itself. It emerged when HttpClient was still clunky and underpowered, offering a cleaner, object-oriented API for building requests, serializing bodies, and handling responses without a lot of boilerplate. RestSharp 110+ (the current active branch) has been modernized for .NET 6 and later - it supports System.Text.Json natively and has shed much of its legacy weight. But it remains a third-party dependency, and some teams now question whether it earns its place when the built-in stack has caught up substantially.
Refit takes a fundamentally different approach: it lets you define your HTTP API as a C# interface with attributes, and at runtime (or via compile-time source generation in Refit 7+) it generates a concrete implementation for you. If you have ever used Retrofit for Android or Feign for Java, Refit follows the same mental model. You describe the contract; Refit handles the mechanics. This is particularly powerful in microservices architectures where you maintain typed clients for each downstream service.
Side-By-Side Comparison
The following table covers the dimensions that matter most to enterprise teams:
| Dimension |
HttpClient + IHttpClientFactory |
RestSharp |
Refit |
| Dependency |
Built-in (.NET) |
NuGet package |
NuGet package |
| Setup verbosity |
Medium (typed client class + registration) |
Low-medium (fluent builder) |
Low (interface + attribute) |
| Type safety |
Manual (you write the typed client) |
Manual |
Enforced by interface contract |
| Source generation (AOT) |
Native |
Limited |
Full via Refit.SourceGenerator (v7+) |
| DI integration |
Native via AddHttpClient<T>() |
Manual or via extension |
Native via services.AddRefitClient<T>() |
| Resilience (Polly) |
Built-in via AddStandardResilienceHandler() |
Manual via DelegatingHandler |
Via DelegatingHandler or wrapper |
| Serialization |
System.Text.Json (default), pluggable |
System.Text.Json / Newtonsoft, pluggable |
System.Text.Json (default), Newtonsoft via setting |
| Auth header injection |
Via DelegatingHandler |
Built-in Authenticator abstraction |
Via DelegatingHandler or AuthorizationMessageHandler |
| Testing / mocking |
Mock HttpMessageHandler |
Mock HttpMessageHandler or wrap IRestClient |
Mock the interface directly |
| Performance |
Highest (no abstraction layer) |
Good |
Good (source-gen removes reflection cost) |
| Maintenance risk |
Zero (owned by Microsoft) |
Community-maintained (active) |
Community-maintained (active) |
| Learning curve |
Moderate (understand handler pipeline) |
Low |
Very low for consumers, low for maintainers |
When Should You Use HttpClient with IHttpClientFactory?
IHttpClientFactory with typed clients is the right answer when you value zero additional dependencies, maximum control over the HTTP pipeline, and direct integration with Microsoft's resilience primitives. It shines in these scenarios:
- SDK or library development - when you are building a NuGet package or shared library that other teams will consume, shipping with a zero-dependency typed client avoids transitive dependency conflicts.
- Performance-critical paths - no abstraction overhead, full control over connection pooling and message handler ordering.
- Teams already using
Microsoft.Extensions.Http.Resilience - the built-in resilience pipeline (AddStandardResilienceHandler) integrates cleanly with typed clients, covering retry, circuit breaking, hedging, and timeout in a single call.
- Native AOT deployment - IHttpClientFactory is fully AOT-safe; source-generated Refit is too, but vanilla RestSharp has limitations.
- Standardization under a single vendor - if your organization's policy is to minimize third-party dependencies for security or audit reasons, staying on the built-in stack simplifies governance.
The main downside is verbosity. Every typed client requires a dedicated class with constructor injection, method wrappers, serialization logic, and URL building. For teams managing dozens of downstream service clients, this becomes significant boilerplate.
When Should You Use RestSharp?
RestSharp earns its place on teams that need expressive, readable HTTP code without the ceremony of writing typed client classes from scratch. Its fluent request builder is genuinely ergonomic, and its Authenticator abstraction handles OAuth token refresh, API key injection, and custom header schemes without hand-rolling DelegatingHandler pipelines.
RestSharp is a strong fit when:
- You are migrating legacy .NET Framework code - RestSharp has a long history, and many enterprise codebases already use it. Upgrading to RestSharp 110+ is typically far less disruptive than rewriting to typed clients or Refit.
- Your HTTP usage is script-like or one-off - integration tests, admin utilities, CLI tools, or data migration scripts where you want to fire a request without DI wiring.
- Team prefers an imperative, builder-style API - developers who think in terms of "build a request, execute it, handle the response" find RestSharp's model natural.
- You need flexible auth without writing handlers - RestSharp's
IAuthenticator interface is clean and well-documented.
Where RestSharp loses ground: it adds a third-party dependency that must be updated, reviewed, and tracked in your software bill of materials (SBOM). Teams that have standardized on source generation for AOT workloads will also find RestSharp requires additional effort to make it compatible.
When Should You Use Refit?
Refit delivers the highest developer productivity for teams that are consuming well-defined external or internal REST APIs. Defining an interface, decorating it with [Get], [Post], [Headers], and [Authorize] attributes, and letting Refit wire up the implementation eliminates an entire category of boilerplate. On large microservices platforms, this compounds: if you have 15 service-to-service clients, writing them in Refit versus typed HttpClient classes saves hundreds of lines of production code.
Use Refit when:
- You have many typed service clients - the interface-first model scales across a large number of downstream APIs without repetition.
- You want mock-friendly HTTP clients by default - because Refit clients are interfaces, mocking them in unit tests is trivial with any mocking framework. No need to inject mock
HttpMessageHandler chains.
- Your API is OpenAPI-described - code generators (NSwag, Kiota) can produce Refit interfaces directly from OpenAPI specs, making Refit a natural fit for contract-first teams.
- You are targeting Native AOT - Refit 7's source generator produces fully AOT-safe client implementations with no reflection at runtime.
- Productivity and onboarding speed matter - junior developers can add a new endpoint to a Refit interface in minutes, with compile-time validation of parameter matching and return type consistency.
Refit's limitations are worth naming: it is less flexible for non-standard request shapes (file uploads, multipart forms, streaming) compared to writing a typed client by hand, and the attribute-driven approach can feel constraining if you need dynamic request construction.
Real-World Trade-Offs: What SERP Results Don't Tell You
Most comparison articles cover feature tables. Here are the trade-offs that actually surface in enterprise code reviews:
Error handling discipline. All three options require you to define and enforce your own error-handling contract. Refit throws ApiException by default; you can configure ExceptionFactory or return IApiResponse<T> for explicit result handling. HttpClient typed clients force you to write the mapping yourself. RestSharp provides RestResponse.IsSuccessful and RestResponse.ErrorException but doesn't enforce a convention. Teams that invest in a consistent result pattern (e.g., ErrorOr<T>, FluentResults) across their service clients tend to end up with more maintainable code regardless of which HTTP client they choose.
Resilience and retry. Microsoft's AddStandardResilienceHandler() hooks into the IHttpClientFactory pipeline natively and is the most opinionated (and well-tested) option. With Refit and RestSharp, you attach a DelegatingHandler for Polly. This is not difficult, but it is less discoverable for teams new to the pattern.
Connection lifecycle in long-running services. Regardless of which library you use, the underlying socket lifecycle management is provided by HttpMessageHandler pooling in IHttpClientFactory. Both Refit and RestSharp (modern versions) support being registered via IHttpClientFactory, which means they all benefit from the same connection hygiene - as long as your team registers them correctly.
Observability. ASP.NET Core's built-in OpenTelemetry instrumentation (Microsoft.Extensions.Http) captures HTTP client spans for typed clients with no additional setup. Refit clients registered via IHttpClientFactory inherit this automatically. RestSharp does not emit OpenTelemetry spans out of the box and requires custom handler instrumentation.
Is RestSharp Obsolete in 2026?
This question surfaces in the .NET community regularly. The short answer: not quite, but its value proposition has narrowed. For greenfield services, the built-in stack or Refit covers the vast majority of use cases better. RestSharp's primary remaining advantages are familiarity and ease of use in non-DI contexts. Teams maintaining existing RestSharp code should upgrade to v110+ (which supports modern .NET properly) rather than rewriting for rewriting's sake, but new services should default to either typed HttpClient or Refit.
The Recommendation: Which One Should Your Team Use?
There is no universal winner - but there are clear guidelines:
| Your situation |
Recommended option |
| Greenfield microservices with many service clients |
Refit |
| SDK / shared library development |
HttpClient + IHttpClientFactory |
| Native AOT workloads |
HttpClient + IHttpClientFactory or Refit 7+ |
| Migrating existing legacy code |
Keep or upgrade RestSharp |
| Teams that prize zero third-party dependencies |
HttpClient + IHttpClientFactory |
| Maximum testability with minimal ceremony |
Refit |
| Scripts, admin tools, integration test utilities |
RestSharp or HttpClient directly |
For most enterprise API platforms in 2026, the pragmatic default is: use Refit for service-to-service typed clients and keep IHttpClientFactory as the foundation underneath. Refit 7 source-generates its clients via IHttpClientFactory, giving you the best of both worlds - Refit's ergonomics layered on top of Microsoft's production-hardened HTTP infrastructure.
Frequently Asked Questions
Does Refit work with IHttpClientFactory?
Yes. Refit's AddRefitClient<T>() extension method registers the client via IHttpClientFactory under the hood. You get Refit's interface-driven ergonomics and IHttpClientFactory's connection pooling, lifecycle management, and resilience handler integration simultaneously.
Is RestSharp thread-safe?
RestSharp's RestClient is designed to be used as a singleton or per-named-client instance. It is thread-safe for concurrent requests, but you should not share a single RestClient instance across requests that require different base URLs or authentication configurations without creating separate instances.
When should I use raw HttpClient instead of Refit or RestSharp?
Use raw HttpClient (via a typed client class) when you need maximum control over request construction - streaming responses, multipart uploads, non-standard serialization, or when you are building a library that must not bring in third-party NuGet dependencies.
Can Refit handle multipart file uploads?
Refit supports multipart form data via [Multipart] and StreamPart / ByteArrayPart parameter types. It covers common upload scenarios, but for complex streaming or chunked upload workflows, a hand-written typed client gives you more granular control over the request body.
How do I add retry logic to a Refit client in ASP.NET Core?
Register your Refit client via AddRefitClient<T>(), then chain .AddStandardResilienceHandler() (from Microsoft.Extensions.Http.Resilience) or .AddPolicyHandler() (from Polly) on the resulting IHttpClientBuilder. The resilience pipeline attaches to the underlying HttpMessageHandler and applies to all requests made through that client.
Does RestSharp support .NET 8 and .NET 10?
RestSharp 110+ targets .NET 6+ and is actively maintained for current LTS and STS releases. There are no known blockers for .NET 8 or .NET 10 compatibility, but teams should track the project's GitHub for updates as new .NET versions ship.
What is the performance difference between Refit and HttpClient?
With Refit 7's source generator enabled, the performance overhead versus a hand-written typed client is negligible - source generation eliminates the runtime reflection that earlier Refit versions used. In practical benchmarks on enterprise-scale services, the difference is not a differentiating factor in real workloads; network latency and serialization dominate by orders of magnitude.
Should I use Refit for external third-party API clients?
Yes, Refit is well-suited for external API clients - particularly when the provider publishes an OpenAPI spec, allowing you to generate the Refit interface automatically with a tool like NSwag or Kiota. You get a typed, mock-friendly client that tracks the API contract and can be regenerated as the spec evolves.
About the Author
Celin Daniel is Co-founder of Coding Droplets with 13+ years of hands-on experience building, shipping, and operating .NET and ASP.NET Core systems in production. The guidance here comes from real projects and production incidents, not theory.
