IActionResult vs Typed Results in ASP.NET Core – Which One Should You Use?

In ASP.NET Core, building a clean and maintainable API is all about clarity, testability, and flexibility.

A major design decision you'll often face is:

Should I return IActionResult or a typed result like ActionResult<T> or just the model itself?

This blog post dives deep into:

• What each return type means

• Their usage and behavior

• Best practices with examples

• Which one is better for your use case

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What is IActionResult?

IActionResult is an interface that defines a contract for HTTP responses in ASP.NET Core. It's the most flexible way to return different response types (e.g., Ok(), NotFound(), BadRequest()).

🧑‍💻 Example:

[HttpGet("{id}")]
public IActionResult GetProduct(int id)
{
    var product = _repo.GetById(id);
    if (product == null)
        return NotFound();

    return Ok(product);
}

✅ Pros:

• Great for returning multiple status codes

• Explicit and clear control over responses

• Perfect for APIs with multiple possible outcomes

❌ Cons:

• Less clarity in return type (no compile-time enforcement of output type)

• Needs casting or assumptions in consumers (e.g., tests)

What is a Typed Result (ActionResult<T> or just T)?

ASP.NET Core 2.1+ introduced typed action results like ActionResult<T>, which combine the power of IActionResult with type inference for models.

You can return both the model (e.g., Product) and use return helpers (NotFound(), BadRequest()) in the same method.

🧑‍💻 Example:

[HttpGet("{id}")]
public ActionResult<Product> GetProduct(int id)
{
    var product = _repo.GetById(id);
    if (product == null)
        return NotFound();

    return product; // automatically wrapped as Ok(product)
}

✅ ASP.NET Core will:

• Wrap the Product into an OkObjectResult

• Allow you to still return NotFound() or BadRequest()

✅ Pros:

• Type-safe — helps Swagger/OpenAPI and client-side tools

• Cleaner and more concise code

• Works great with minimal APIs and newer patterns

❌ Cons:

• Slightly less control if advanced customization is needed

• Some developers find return product; ambiguous (though it's valid)

Example: Return Types in Real-World Controller

IActionResult Version:

[HttpPost]
public IActionResult CreateProduct(Product product)
{
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    var created = _repo.Add(product);
    return CreatedAtAction(nameof(GetProduct), new { id = created.Id }, created);
}

ActionResult<Product> Version:

[HttpPost]
public ActionResult<Product> CreateProduct(Product product)
{
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    var created = _repo.Add(product);
    return CreatedAtAction(nameof(GetProduct), new { id = created.Id }, created);
}

What About Minimal APIs?

In ASP.NET Core Minimal APIs:

app.MapGet("/products/{id}", (int id, IRepo repo) =>
{
    var product = repo.GetById(id);
    return product is not null ? Results.Ok(product) : Results.NotFound();
});

✅ This uses Results<T> which is similar in spirit to ActionResult<T> — combining strong typing with response semantics.

Best Practices

• Use ActionResult<T> when:

  • You're building REST APIs with Swagger/OpenAPI

  • You want both strong typing and status code control

  • You're working in Minimal API or modern ASP.NET Core

• Use IActionResult when:

  • You need very dynamic response logic

  • You want full control over return types without model constraints

  • You're building UI-heavy MVC apps with Views

Extra Tip: Return Type Matters for Client SDKs

Using ActionResult<T> improves API consumers like:

• Swagger UI

• NSwag / Swashbuckle

• AutoRest / OpenAPI code generators

This ensures clients know what to expect, not just a generic response blob.

Final Thoughts

Choosing the right return type is more than just syntax — it’s about:

• Clarity

• Client experience

• Maintainability

🔁 Need flexibility? → IActionResult
🧾 Need clarity and Swagger support? → ActionResult<T>

Mastering both gives you the flexibility and power to write APIs that are robust, discoverable, and cleanly structured.