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 and specify an output file for the generated Rust code.

oas3-gen generate --input <path/to/openapi.json> --output <path/to/generated_types.rs>

Example

Consider the following OpenAPI schema definition in schemas/pet.json:

{
  "Pet": {
    "type": "object",
    "description": "Represents a pet in the store.",
    "required": ["id", "name"],
    "properties": {
      "id": {
        "type": "integer",
        "format": "int64",
        "description": "The unique identifier for the pet."
      },
      "name": {
        "type": "string",
        "description": "The name of the pet."
      },
      "tag": {
        "type": "string",
        "description": "An optional tag for the pet."
      }
    }
  }
}

Executing oas3-gen produces the corresponding Rust types.

// src/generated_types.rs

use serde::{Deserialize, Serialize};

/// Represents a pet in the store.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Pet {
    /// The unique identifier for the pet.
    pub id: i64,
    /// The name of the pet.
    pub name: String,
    /// An optional tag for the pet.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tag: Option<String>,
}

Key Features

• Comprehensive OpenAPI 3.1 Support: Parses schemas, parameters, request bodies, and responses from the latest OpenAPI specification.
• Idiomatic Code Generation: Creates Rust structs and enums that follow common language conventions.
• Serde Integration: Automatically derives serde::Serialize and serde::Deserialize for immediate use with JSON and other data formats.
• Documentation Generation: Converts OpenAPI schema descriptions directly into Rust documentation comments.
• Complex Schema Resolution: Correctly handles allOf, oneOf, and anyOf compositions to generate accurate and complex type definitions.
• Cycle Detection: Intelligently detects and manages cyclical dependencies between schemas, preventing infinite recursion in type definitions.
• Convention-Aware Naming: Detects camelCase and snake_case in the source schema and applies the appropriate #[serde(rename_all = "...")] attribute.
• Operation Scaffolding: Generates types for API operation parameters, request bodies, and responses.
• Validation Support: Translates OpenAPI constraints (e.g., minLength, maxLength, pattern, minimum, maximum) into validation attributes.
• Enhanced CLI Experience: Provides colored, timestamped output with automatic theme detection for improved readability in various terminal environments.
• Operation Filtering: Selectively generate code for specific operations using --only or exclude operations with --exclude for fine-grained control.

Command-Line Options

OpenAPI to Rust code generator

Usage: oas3-gen [OPTIONS] <COMMAND>

Commands:
  list      List information from OpenAPI specification
  generate  Generate Rust code from OpenAPI specification
  help      Print this message or the help of the given subcommand(s)

Options:
      --color <COLOR>  Control color output [default: auto] [possible values: always, auto, never]
      --theme <THEME>  Terminal theme (dark or light background) [default: auto] [possible values: dark, light, auto]
  -h, --help           Print help
  -V, --version        Print version

Generate Command

Generate Rust code from OpenAPI specification

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

Options:
  -i, --input <FILE>             Path to the OpenAPI JSON specification file
  -o, --output <FILE>            Path where the generated Rust code will be written
      --visibility <VISIBILITY>  Visibility level for generated types [default: public]
  -v, --verbose                  Enable verbose output with detailed progress information
  -q, --quiet                    Suppress non-essential output (errors only)
      --all-schemas              Generate all schemas defined in the spec, including unreferenced schemas.
                                 When combined with --only or --exclude, this includes all schemas even if
                                 they are not referenced by the filtered operations (default: only schemas
                                 reachable from included operations)
      --only <IDS>               Include only specific operations for generation (comma-separated stable IDs)
      --exclude <IDS>            Exclude specific operations from generation (comma-separated stable IDs)
  -h, --help                     Print help

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 with automatic color and theme detection
oas3-gen generate -i openapi.json -o generated.rs

# Verbose output showing detailed statistics
oas3-gen generate -i openapi.json -o generated.rs --verbose

# Force dark theme with always-on colors
oas3-gen generate -i openapi.json -o generated.rs --theme dark --color always

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

# Quiet mode (errors only)
oas3-gen generate -i openapi.json -o generated.rs --quiet

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

# Generate code for specific operations only
oas3-gen generate -i openapi.json -o generated.rs --only createUser,getUser,updateUser

# Generate code excluding certain operations
oas3-gen generate -i openapi.json -o generated.rs --exclude deleteUser,listUsers

# Generate all schemas but only specific operations (includes unreferenced schemas)
oas3-gen generate -i openapi.json -o generated.rs --all-schemas --only createUser

# 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.

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.x]: https://spec.openapis.org/oas/v3.1.1