OpenAPI Nexus

OpenAPI 3.0 / 3.1 / 3.2 to multi-language code generator

OpenAPI Nexus transforms OpenAPI specifications into type-safe client libraries. Generated output is deterministic, compile-checked in CI, and tested byte-for-byte via golden tests.

Language Support

Quick Start

Install

Download a binary from the releases page, or build from source:

cargo install openapi-nexus

Requires Rust 1.90+.

Generate

# TypeScript client
openapi-nexus generate -i spec.yaml -o output -g typescript-fetch

# Go client
openapi-nexus generate -i spec.yaml -o output -g go-http

# Rust client (reqwest)
openapi-nexus generate -i spec.yaml -o output -g rust-reqwest

# Python client (httpx)
openapi-nexus generate -i spec.yaml -o output -g python-httpx

# Java client
openapi-nexus generate -i spec.yaml -o output -g java-okhttp

# Multiple generators at once
openapi-nexus generate -i spec.yaml -o output -g typescript-fetch,go-http,rust-reqwest

Configuration

Configuration resolves in order: CLI args > environment variables (OPENAPI_NEXUS_*) > config file (openapi-nexus-config.toml) > defaults.

# Environment variables
export OPENAPI_NEXUS_INPUT="spec.yaml"
export OPENAPI_NEXUS_OUTPUT="generated"
export OPENAPI_NEXUS_GENERATOR="typescript-fetch"

Generator-specific options go in the config file:

[generators.go-http]
module_path = "github.com/myorg/myproject/sdk"

[generators.rust-reqwest]
workspace_mode = true
workspace_deps = "workspace_version"

[generators.rust-reqwest.extra_derives.structs]
derives = ["PartialEq"]

[generators.rust-reqwest.extra_derives.enums]
derives = ["Hash"]

[generators.rust-reqwest.utoipa]
enabled = true
dependency = '{ version = "5" }'

[generators.typescript-fetch]
emit_enum_constants = true
emit_type_guards = true

How It Works

OpenAPI YAML/JSON → parse → lower to IR → CodeGenerator::generate(&IrSpec) → write

Parsing auto-detects OAS version (3.0, 3.1, 3.2). Lowering produces a version-agnostic IrSpec. Each generator receives the pre-lowered IR and uses sigil-stitch for type-safe code emission.

Documentation

Full documentation is available at the project docs site.

Development

# Run all tests
cargo test

# Clippy (required before commit)
cargo clippy --all-targets --all-features -- -D warnings

# Update golden files after intentional output changes
UPDATE_GOLDEN=1 cargo test

# Compile-check generated output for all languages
just golden-build-all

License

Dual-licensed under MIT or Apache-2.0 at your option.