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Build with Smithy.

Define your API once in a clear, protocol-agnostic language. Smithy generates type-safe clients, servers, and docs across ten languages from a single model, and it powers the APIs and SDKs at AWS.

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Open source, Apache 2.0
Created and used at AWS
10+ languages

weather.smithy

$version: "2"namespace example.weather service Weather {    version: "2006-03-01"    resources: [City]} resource City {    identifiers: { cityId: CityId }    read: GetCity    list: ListCities} @readonlyoperation GetCity {    input := {        @required        cityId: CityId    }    output := {        @required        name: String    }}

Write your API once. Generate everything.

One model in. SDKs, servers, docs, and OpenAPI out. smithy build does the rest.

Smithy model weather.smithy

smithy build

Client SDKs 10 languages
Servers TypeScript, Java
Documentation API reference
OpenAPI & JSON Schema

Client SDKs ship in ten languages

TypeScript

Python

Rust

Kotlin

Swift

Java

Scala

Ruby

Dafny

Protocol-agnostic by design

One model describes the shapes; the protocol decides the wire format. The same service serves REST JSON, RPC v2 CBOR, AWS JSON, and query/XML, so you can adopt new protocols without touching the model.

Explore protocols

GET /cities/sea-01

content-type: application/json

{
  "name": "Seattle",
  "coordinates": {
    "latitude": 47.6062,
    "longitude": -122.3321
  }
}

POST /service/Weather/operation/GetCity

smithy-protocol: rpc-v2-cbor

// CBOR is binary; shown decoded
{
  name: "Seattle",
  coordinates: { latitude: 47.6062, longitude: -122.3321 }
}

POST /

x-amz-target: Weather.GetCity

content-type: application/x-amz-json-1.0

{
  "name": "Seattle",
  "coordinates": { "latitude": 47.6062, "longitude": -122.3321 }
}

POST / · application/x-www-form-urlencoded

Action=GetCity&cityId=sea-01

<!-- XML response -->
<GetCityResult>
  <name>Seattle</name>
  <coordinates>
    <latitude>47.6062</latitude>
  </coordinates>
</GetCityResult>

Declarative API governance

Your standards live in the model, not in an external linter, so they are validated by smithy build itself and cannot be bypassed. Share the rules org-wide and catch design and quality issues before your customers do.

Read the guides

zsh: smithy build

$smithy build

Validating model (142 shapes)…

✓RestJson1 protocol traits resolved

✓All operations have documentation

✓Pagination tokens type-checked

✕ ERRORMissingPaginatedTrait

ListCities returns a list but is not @paginated

at example.weather#ListCities (weather.smithy:24)

1 error, 0 warnings. Build failed.

Backward-compatible evolution

Extend the meta-model through traits to capture more about your services without breaking changes. Smithy checks every revision for backward compatibility.

Explore traits

weather.smithy · diff

@error("client") @retryable structure ThrottlingError { @required message: String }

✓ Backward-compatible. No breaking change.

Resource-based modeling

Model your API as resources and operations. Smithy uses that structure to generate richer artifacts, from CloudFormation schemas to type-safe SDKs and docs.

Model resources

model explorer

service Weather
resource City
read · GetCity
list · ListCities
operation GetCurrentTime

Smithy is the cornerstone of cross-team collaboration in our organization. The simplicity of the base language, rich extensibility, and the ease of writing correct tooling make it a must-try for organizations that want to evolve their APIs safely and efficiently.

SiriusXM

Supported languages

Clients and servers, in your language.

One model compiles to idiomatic, type-safe code. No hand-written glue.

Clients · 10

Servers · 5

Build your first SDK in minutes.

Start with the quickstart, or read the full specification.

Get Started Read the specification

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