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utoipa - Auto-generated OpenAPI documentation

Utoipa build crates.io docs.rs MSRV

Pronounced /ju:ˈtoʊ:i.pɑ/ or /ju:ˈtoʊˌaɪ.piˈeɪ/ whatever works better for you.

Want to have your API documented with OpenAPI? But don't want to be bothered with manual YAML or JSON tweaking? Would like it to be so easy that it would almost be utopic? Don't worry: utoipa is here to fill this gap. It aims to do, if not all, then most of the heavy lifting for you, enabling you to focus on writing the actual API logic instead of documentation. It aims to be minimal, simple and fast. It uses simple proc macros which you can use to annotate your code to have items documented.

The utoipa crate provides auto-generated OpenAPI documentation for Rust REST APIs. It treats code-first approach as a first class citizen and simplifies API documentation by providing simple macros for generating the documentation from your code.

It also contains Rust types of the OpenAPI spec, allowing you to write the OpenAPI spec only using Rust if auto generation is not your flavor or does not fit your purpose.

Long term goal of the library is to be the place to go when OpenAPI documentation is needed in any Rust codebase.

Utoipa is framework-agnostic, and could be used together with any web framework, or even without one. While being portable and standalone, one of its key aspects is simple integration with web frameworks.

Choose your flavor and document your API with ice-cold IPA

Refer to the existing examples for building the "todo" app in the following frameworks:

All examples include a Swagger-UI unless stated otherwise.

There are also examples of building multiple OpenAPI docs in one application, each separated in Swagger UI. These examples exist only for the actix and warp frameworks.

Even if there is no example for your favourite framework, utoipa can be used with any web framework which supports decorating functions with macros similarly to the warp and tide examples.

Community examples

What's up with the word play?

The name comes from the words utopic and api where uto are the first three letters of utopic and the ipa is api reversed. Aaand... ipa is also an awesome type of beer 🍺.

Crate Features

  • yaml Enables serde_yaml serialization of OpenAPI objects.
  • actix_extras Enhances actix-web integration with being able to parse path, path and query parameters from actix web path attribute macros. See docs or examples for more details.
  • rocket_extras Enhances rocket framework integration with being able to parse path, path and query parameters from rocket path attribute macros. See docs or examples for more details.
  • axum_extras Enhances axum framework integration allowing users to use IntoParams without defining the parameter_in attribute. See docs or examples for more details.
  • debug Add extra traits such as debug traits to openapi definitions and elsewhere.
  • chrono Add support for chrono DateTime, Date, NaiveDate, NaiveDateTime, NaiveTime and Duration types. By default these types are parsed to string types with additional format information. format: date-time for DateTime and NaiveDateTime and format: date for Date and NaiveDate according RFC3339 as ISO-8601. To override default string representation users have to use value_type attribute to override the type. See docs for more details.
  • time Add support for time OffsetDateTime, PrimitiveDateTime, Date, and Duration types. By default these types are parsed as string. OffsetDateTime and PrimitiveDateTime will use date-time format. Date will use date format and Duration will not have any format. To override default string representation users have to use value_type attribute to override the type. See docs for more details.
  • decimal Add support for rust_decimal Decimal type. By default it is interpreted as String. If you wish to change the format you need to override the type. See the value_type in component derive docs.
  • decimal_float Add support for rust_decimal Decimal type. By default it is interpreted as Number. This feature is mutually exclusive with decimal and allow to change the default type used in your documentation for Decimal much like serde_with_float feature exposed by rust_decimal.
  • uuid Add support for uuid. Uuid type will be presented as String with format uuid in OpenAPI spec.
  • ulid Add support for ulid. Ulid type will be presented as String with format ulid in OpenAPI spec.
  • url Add support for url. Url type will be presented as String with format uri in OpenAPI spec.
  • smallvec Add support for smallvec. SmallVec will be treated as Vec.
  • openapi_extensions Adds traits and functions that provide extra convenience functions. See the request_body docs for an example.
  • repr Add support for repr_serde's repr(u*) and repr(i*) attributes to unit type enums for C-like enum representation. See docs for more details.
  • preserve_order Preserve order of properties when serializing the schema for a component. When enabled, the properties are listed in order of fields in the corresponding struct definition. When disabled, the properties are listed in alphabetical order.
  • preserve_path_order Preserve order of OpenAPI Paths according to order they have been introduced to the #[openapi(paths(...))] macro attribute. If disabled the paths will be ordered in alphabetical order.
  • indexmap Add support for indexmap. When enabled IndexMap will be rendered as a map similar to BTreeMap and HashMap.
  • non_strict_integers Add support for non-standard integer formats int8, int16, uint8, uint16, uint32, and uint64.
  • rc_schema Add ToSchema support for Arc<T> and Rc<T> types. Note! serde rc feature flag must be enabled separately to allow serialization and deserialization of Arc<T> and Rc<T> types. See more about serde feature flags.

Utoipa implicitly has partial support for serde attributes. See docs for more details.


Add minimal dependency declaration to Cargo.toml.

utoipa = "4"

To enable more features such as use actix framework extras you could define the dependency as follows.

utoipa = { version = "4", features = ["actix_extras"] }

Note! To use utoipa together with Swagger UI you can use the utoipa-swagger-ui crate.


Create a struct, or it could also be an enum. Add ToSchema derive macro to it, so it can be registered as an OpenAPI schema.

use utoipa::ToSchema;

struct Pet {
   id: u64,
   name: String,
   age: Option<i32>,

Create a handler that would handle your business logic and add path proc attribute macro over it.

mod pet_api {
    /// Get pet by id
    /// Get pet from database by pet id
        path = "/pets/{id}",
            (status = 200, description = "Pet found succesfully", body = Pet),
            (status = NOT_FOUND, description = "Pet was not found")
            ("id" = u64, Path, description = "Pet database id to get Pet for"),
    async fn get_pet_by_id(pet_id: u64) -> Pet {
        Pet {
            id: pet_id,
            age: None,
            name: "lightning".to_string(),

Utoipa has support for http StatusCode in responses.

This attribute macro will create another struct named with __path_ prefix + handler function name. So when you implement some_handler function in different file and want to export this, make sure __path_some_handler in the module can also be accessible from the root.

Tie the Schema and the endpoint above to the OpenAPI schema with following OpenApi derive proc macro.

use utoipa::OpenApi;

#[openapi(paths(pet_api::get_pet_by_id), components(schemas(Pet)))]
struct ApiDoc;

println!("{}", ApiDoc::openapi().to_pretty_json().unwrap());

This would produce an API doc something similar to:

  "openapi": "3.0.3",
  "info": {
    "title": "application name from Cargo.toml",
    "description": "description from Cargo.toml",
    "contact": {
      "name": "author name from Cargo.toml",
      "email": "author email from Cargo.toml"
    "license": {
      "name": "license from Cargo.toml"
    "version": "version from Cargo.toml"
  "paths": {
    "/pets/{id}": {
      "get": {
        "tags": ["pet_api"],
        "summary": "Get pet by id",
        "description": "Get pet by id\n\nGet pet from database by pet id\n",
        "operationId": "get_pet_by_id",
        "parameters": [
            "name": "id",
            "in": "path",
            "description": "Pet database id to get Pet for",
            "required": true,
            "deprecated": false,
            "schema": {
              "type": "integer",
              "format": "int64",
              "minimum": 0.0,
        "responses": {
          "200": {
            "description": "Pet found succesfully",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Pet"
          "404": {
            "description": "Pet was not found"
        "deprecated": false
  "components": {
    "schemas": {
      "Pet": {
        "type": "object",
        "required": ["id", "name"],
        "properties": {
          "id": {
            "type": "integer",
            "format": "int64",
            "minimum": 0.0,
          "name": {
            "type": "string"
          "age": {
            "type": "integer",
            "format": "int32",
            "nullable": true,

Modify OpenAPI at runtime

You can modify generated OpenAPI at runtime either via generated types directly or using Modify trait.

Modify generated OpenAPI via types directly.

    info(description = "My Api description"),
struct ApiDoc;

let mut doc = ApiDoc::openapi();
doc.info.title = String::from("My Api");

You can even convert the generated OpenApi to OpenApiBuilder.

let builder: OpenApiBuilder = ApiDoc::openapi().into();

See Modify trait for examples on how to modify generated OpenAPI via it.

Go beyond the surface


Swagger UI returns 404 NotFound from built binary

This is highly probably due to RustEmbed not embedding the Swagger UI to the executable. This is natural since the RustEmbed library does not by default embed files on debug builds. To get around this you can do one of the following.

  1. Build your executable in --release mode
  2. or add debug-embed feature flag to your Cargo.toml for utoipa-swagger-ui. This will enable the debug-emebed feature flag for RustEmbed as well. Read more about this here and here.

Find utoipa-swagger-ui feature flags here.

How to implement ToSchema for external type?

There are few ways around this that are elaborated here in detail.

How to use Rust's type aliases?

At the moment that is not possible due to there is no way to evaluate the actual type behind the type token that is visible to the proc macro code generation. This might be possible in future if a global alias registry can be implemented. Here is an issue related to the topic #766.


Licensed under either of Apache 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, shall be dual licensed, without any additional terms or conditions.


~73K SLoC