Rust OpenAPI 3.1 Type Generator

oas3-gen is a command-line interface (CLI) for generating idiomatic Rust type definitions from an OpenAPI v3.1.x specification. The tool produces clean, production-ready code designed for seamless integration into any Rust project. Its primary function is to provide a robust and reliable method for type generation, ensuring the resulting code is correct, efficient, and well-documented.

Quick Start

1. Installation

Install the tool directly from crates.io using cargo.

cargo install oas3-gen

2. Generation

Provide a path to an OpenAPI specification (JSON or YAML) and specify an output file for the generated Rust code. The format is auto-detected based on file extension.

# generate types (structs and enums)
oas3-gen generate -i path/to/openapi.json -o path/to/types.rs
oas3-gen generate -i path/to/openapi.yaml -o path/to/types.rs

# generate client operations
oas3-gen generate client -i path/to/openapi.json -o path/to/client.rs

Example

Consider the following Pet OpenAPI schema definition in fixtures/petstore.json:

{
  "Pet": {
    "type": "object",
    "required": ["id", "name"],
    "properties": {
     "id": {
      "type": "integer",
      "format": "int64"
     },
     "name": {
      "type": "string"
     },
     "tag": {
      "type": "string"
     }
    }
  }
}

Executing oas3-gen produces the corresponding Rust types.

// src/types.rs

use serde::Deserialize;

#[derive(Debug, Clone, PartialEq, Deserialize, oas3_gen_support::Default)]
pub struct Pet {
  pub id: i64,
  pub name: String,
  pub tag: Option<String>,
}

Key Features

Missing features

• Server Code generation
• OAS 3.1 Links and $dynamic-ref (oas3 doesn't support this yet)
• OAS 3.2 Event-stream support
• External schema references
• HTTP schema references and fetching

Command-Line Options

OpenAPI to Rust code generator

Usage: oas3-gen [OPTIONS] <COMMAND>

Commands:
  list      List information from OpenAPI specification
  generate  Generates idiomatic, type-safe Rust code from an OpenAPI v3.1 (OAS31) specification
  help      Print this message or the help of the given subcommand(s)

Options:
  -h, --help     Print help
  -V, --version  Print version

Terminal Output:
      --color <WHEN>   Coloring [default: auto] [possible values: always, auto, never]
      --theme <THEME>  Theme [default: auto] [possible values: dark, light, auto]

Generate Command

Generates idiomatic, type-safe Rust code from an OpenAPI v3.1 (OAS31) specification

Usage: oas3-gen generate [OPTIONS] --input <FILE> --output <FILE> [MODE]

Arguments:
  [MODE]  Sets the generation mode [default: types] [possible values: types, client, client-mod]

Required:
  -i, --input <FILE>   Path to the OpenAPI specification file
  -o, --output <PATH>  Path for generated output (file for types/client, directory for client-mod)

Code Generation:
  -C, --visibility <PUB>       Module visibility for generated items [default: public] [possible values: public, crate, file]
      --odata-support          Enable OData-specific field optionality rules (makes @odata.* fields optional on concrete types)
      --enum-mode <ENUM_MODE>  Specifies how to handle enum case sensitivity and duplicates [default: merge] [possible values: merge, preserve, relaxed]
      --no-helpers             Disable generation of ergonomic helper methods for enum variants
  -c, --customize <TYPE=PATH>  Custom serde_as type overrides (format: type_name=custom::Path)

Operation Filtering:
      --only <id_1,id_2,...>     Include only the specified comma-separated operation IDs
      --exclude <id_1,id_2,...>  Exclude the specified comma-separated operation IDs
      --all-schemas              Generate all schemas, even those unreferenced by selected operations

List Command

List information from OpenAPI specification

Usage: oas3-gen list <COMMAND>

Commands:
  operations  List all operations defined in the OpenAPI specification
  help        Print this message or the help of the given subcommand(s)

Options:
  -h, --help  Print help

Examples

# Basic usage to generate a client module from a json schema file
oas3-gen generate client-mod -i openapi.json -o generated

# Or generate types and client code individually ...

# Generate types with crate-level visibility
oas3-gen generate types -i openapi.json -o types.rs -C crate
oas3-gen generate client -i openapi.json -o client.rs -C crate

# Generate all schemas types including unused ones
oas3-gen generate -i openapi.json -o types.rs --all-schemas

# Generate code for specific operation types only
oas3-gen generate -i openapi.json -o types.rs --only create_user,get_user,update_user

# Generate code excluding certain operation types
oas3-gen generate -i openapi.json -o types.rs --exclude delete_user,list_users

# Generate all schemas but only specific operation types (includes unreferenced schemas)
oas3-gen generate -i openapi.json -o types.rs --all-schemas --only create_user

# Enable OData support for Microsoft Graph
oas3-gen generate -i graph-api.json -o types.rs --odata-support

# Enable relaxed (case-insensitive) enum deserialization
oas3-gen generate -i openapi.json -o types.rs --enum-mode relaxed

# Enable custom parsing through serde_as traits
oas3-gen generate client-mod -i openapi.json -o generated --customize datetime=MyCustomDateTime

# List all operations in the specification
oas3-gen list operations -i openapi.json

License

This project is licensed under the MIT License. See the LICENSE.md file for details.

Copyright (c) 2026 Individual contributors

Contribution

Contributions are welcome! Please see CONTRIBUTING.md for more details on how to get started.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be licensed as MIT, without any additional terms or conditions.

See [OpenAPI v3.1.2]: https://spec.openapis.org/oas/v3.1.2