# SDK generator comparisons

> Eight SDK generators compared with Voxgig on licensing, language targets, customization, cross-cutting behavior and cost. One page per tool. Published by Voxgig, which makes one of the tools compared. Every page links first-party sources and carries the date its facts were checked. Corrections go to info@voxgig.com. Facts checked 7 September 2026.

## Method

- **Who publishes this.** Voxgig publishes these pages and makes one of the tools compared on them. The sources are linked on every page so the claims can be checked against the vendors' own documentation.
- **Capabilities, not verdicts.** Each page describes what a tool does and what it does not do. Where the two tools differ, the difference is stated and the reader decides which side of it they are on. No tool is scored, and no overall winner is declared.
- **No asterisks in the table.** If a tool has a feature, the table says it has it. No partial ticks and no footnoted almosts. Where a row would need a paragraph to be accurate, it is a paragraph in the page instead of a row in the table.
- **Dated facts, first-party sources.** Every page carries the date its facts were last checked and links the vendor's own pages, including their comparisons of Voxgig. Pricing and tier limits move fastest, so the pages describe the shape of the pricing and link the vendor for the numbers.
- **Sources are named, including their limits.** Claims come from published documentation, public repositories of generated output, and direct use. Each page's caveats say which, and name what has not been tested. No generator here has been benchmarked against a large specification.
- **Corrections are made and dated.** A correction changes the page and moves its checked date. Corrections from maintainers and other vendors carry the most weight, because they come from the people with the best information about the product.

## The field at a glance

| Tool | What it is | Licence | Languages | Cost |
| --- | --- | --- | --- | --- |
| Voxgig | Open-source generator, six output surfaces | MIT | 22 bundled, more from packages | Free |
| OpenAPI Generator | Open source, community governed | Apache 2.0 | 40+ client, 20+ server | Free |
| Speakeasy | Commercial, CLI plus platform | Proprietary | About 10, plus Terraform | Free tier, then paid per language |
| Fern | Open-source CLI, commercial docs platform | Apache 2.0 plus commercial | 9 | Free to generate, paid docs |
| Stainless | Commercial, winding down | Proprietary | 9, including Terraform | No longer sold |
| APIMatic | Commercial platform and portal | Proprietary | 7 | Low entry tier, then paid |
| liblab | Commercial, pipeline focused | Proprietary | 6, plus Terraform | Tiered subscription |
| Kiota | Open source, from Microsoft | MIT | 8, at varying maturity | Free |
| Hey API | Open source, TypeScript only | MIT | TypeScript | Free |

Language counts are targets a tool ships, not a quality measure: a target existing says nothing about how well it is maintained or how idiomatic its output is. Voxgig's 22 is the number of language targets the generator bundles, listed in https://github.com/voxgig/sdkgen.

## The comparisons

- [OpenAPI Generator](https://voxgig.com/sdk/comparisons/openapi-generator): The community generator most APIs have shipped an SDK from at least once. Apache 2.0, community governed, and broader than everything else here put together: 40+ client languages, 20+ server frameworks, plus docs, Postman collections and Protobuf. Breadth is the whole point, and the cost of it.
- [Speakeasy](https://voxgig.com/sdk/comparisons/speakeasy): Commercial SDK generation with the widest non-SDK output in this comparison. A closed-source generator behind a CLI you run in your own CI, sold per language. Generates Terraform providers and MCP servers as well as SDKs, and expresses customization as OpenAPI Overlays rather than a private config format.
- [Fern](https://voxgig.com/sdk/comparisons/fern): SDKs and a documentation site from one definition. Part of Postman since January 2026. An Apache 2.0 CLI and generator set with a commercial hosted documentation platform on top. Takes OpenAPI, AsyncAPI, gRPC and OpenRPC, or its own definition format, and is the best integrated docs and SDK story in this comparison.
- [Stainless](https://voxgig.com/sdk/comparisons/stainless): The generator behind many of the best-known AI SDKs. Its hosted product is winding down. Stainless generated the official client libraries for OpenAI, Anthropic, Cloudflare and several hundred other providers, and set the quality bar this whole field now aims at. Anthropic acquired it in May 2026 and is winding down the hosted generator.
- [APIMatic](https://voxgig.com/sdk/comparisons/apimatic): The longest-running commercial generator here, and the only one that converts between description formats. SDKs in seven languages, a developer portal, spec validation, and API Transformer, which converts API descriptions between more than fifteen formats. The lowest entry price of the commercial tools on this site.
- [liblab](https://voxgig.com/sdk/comparisons/liblab): SDK generation shaped as a release pipeline. Part of Postman since November 2025. Commercial SDK generation whose centre of gravity is publishing rather than generating: version, changelog and push packages to npm, PyPI, Maven and NuGet on every spec change. Acquired by Postman in November 2025.
- [Kiota](https://voxgig.com/sdk/comparisons/kiota): Microsoft's client generator, built so you do not need a separate SDK per API. MIT, from Microsoft, and pointed at the other side of the API. Kiota is for the team calling somebody else's API, with one shared HTTP stack and fluent request builders across every API you consume.
- [Hey API](https://voxgig.com/sdk/comparisons/hey-api): The TypeScript ecosystem's generator. One language, done properly. MIT, TypeScript only, millions of weekly npm downloads. A plugin architecture that generates exactly what you ask for: types, a client, Zod schemas, TanStack Query hooks. On TypeScript specifically it is the more specialised tool.

## What the decision usually turns on

Five questions, and only one of them is about generated code.

1. Who owns the generator. A vendor tool means a subscription, a roadmap and someone to escalate to. An open-source generator in your repository means maintenance you take on yourself.
2. How many languages you will genuinely ship. Two languages makes per-language subscription pricing cheap. Seven makes it the largest line on the page.
3. What happens on the fortieth change to your API description. This is where hand-written and AI-written SDKs stop being comparable to generated ones, and where a generator that cannot preserve customizations starts costing more than it saves.
4. Whether agents need to call your API. An MCP server generated from the same description as the SDK cannot drift from it; a hand-written one drifts on the next release. Of the tools compared here, Speakeasy and Voxgig generate one. Stainless did too, and its hosted generator is winding down.
5. What you do when the vendor is bought. In the ten months to May 2026, three of the tools compared here changed hands: liblab to Postman in November 2025, Fern to Postman in January 2026, and Stainless to Anthropic in May 2026, with its hosted generator winding down the day it was announced.

## The risk of choosing Voxgig

Point five applies to Voxgig as well. Voxgig Ltd is a small independent company trading since 2018, with no external owner and no support contract on offer. If development stopped, the generator is MIT on npm and GitHub and the generated code is already in the consuming repository, so builds continue and regeneration continues; what stops is development. A smaller project also means a smaller community: fewer answered questions in public, fewer engineers who have hit a given edge case before. A commercial vendor offers a support contract and an SLA against that.

## The wider field

Tools without a page of their own, with a line each. Each is here because it solves an adjacent problem, or because there is not enough direct experience of it here to compare it in detail.

- [Swagger Codegen](https://github.com/swagger-api/swagger-codegen): The ancestor of most of this field, still maintained by SmartBear. OpenAPI Generator forked from it in 2018 and took most of the community. Worth knowing which one you are actually running, because plenty of build files still say this one.
- [AutoRest](https://github.com/Azure/autorest): Microsoft's older generator, built around Azure's needs and still used across the Azure SDKs. Superseded by Kiota for general client generation, and a lot of production code depends on it.
- [NSwag](https://github.com/RicoSuter/NSwag): The .NET ecosystem's long-running toolchain: C# and TypeScript clients, plus server-side specification generation from ASP.NET controllers. Generating the description from the code rather than the other way round is a legitimate workflow that none of the tools above serve.
- [openapi-typescript and openapi-fetch](https://openapi-ts.dev): Types straight from the specification, plus a tiny typed fetch wrapper. Not really a generator: no client class, no features, almost no output. For a lot of TypeScript projects that is exactly the right amount of tool.
- [orval and Kubb](https://orval.dev): Two more TypeScript generators aimed at frontend data layers, with React Query, SWR and MSW mock output. Same territory as Hey API, different opinions about it.
- [openapi-python-client](https://github.com/openapi-generators/openapi-python-client): A single-language generator for Python that produces markedly more idiomatic output than a general-purpose tool aiming at forty languages. The same argument Hey API makes for TypeScript, made for Python.
- [Progenitor](https://github.com/oxidecomputer/progenitor): Oxide's Rust generator, emitting a client as a procedural macro or a build step. Narrow, sharp, and the reference for what generated Rust should look like.
- [Smithy](https://smithy.io): AWS's protocol-agnostic interface definition language, designed for code generation rather than adapted to it, and the model behind the AWS SDKs. The closest thing in the industry to Voxgig's semantic model argument, arrived at independently and at a much larger scale. It converts to OpenAPI, so it can feed the tools above.
- [TypeSpec](https://typespec.io): Microsoft's language for describing APIs concisely and emitting OpenAPI, Protobuf and JSON Schema from one definition. Solves the same authoring problem as Fern Definition, in the open, with an emitter model. Increasingly the front end other people's generators are pointed at.
- [Sideko and Konfig](https://sideko.dev): Smaller commercial entrants in the same shape as Speakeasy and Fern: SDKs plus documentation, per-seat or per-language. For any vendor of this size, including Voxgig, check it is still trading before building a release pipeline on it.
- [Buf and Connect](https://buf.build): If your API is gRPC or Protobuf, generation is already the normal way of life and the toolchain is mature. Worth knowing that the whole argument on this site, that clients should be generated from a machine-readable description, was settled years ago in that world.

## Corrections

Corrections go to info@voxgig.com with a subject of "Comparison correction", or as an issue on the generator repository at https://github.com/voxgig/sdkgen/issues. The most useful correction names the page, the sentence, what is wrong, and where the correct answer is published. A correction changes the page and moves its checked date.

## Where to go next

- [Voxgig SDK Generator](https://voxgig.com/sdk)
- [SDK features](https://voxgig.com/sdk/features)
- [SDK customization](https://voxgig.com/sdk/custom)
- [SDK Catalog, 600+ worked examples](https://voxgig.com/voxgig-sdk)
- [Contact](https://voxgig.com/contact)