@willh/quicktype

quicktype generates strongly-typed models and serializers from JSON, JSON Schema, TypeScript, and GraphQL queries, making it a breeze to work with JSON type-safely in many programming languages.

• Try quicktype in your browser.
• Read 'A first look at quicktype' for more introduction.
• If you have any questions, check out the FAQ first.

Supported Inputs

JSON	JSON API URLs	JSON Schema

TypeScript	GraphQL queries

Target Languages

Ruby	JavaScript	Flow	Rust	Kotlin

Dart	Python	C#	Go	C++

Java	TypeScript	Swift	Objective-C	Elm

JSON Schema	Pike	Prop-Types	Haskell

Missing your favorite language? Please implement it!

Installation

There are many ways to use quicktype. app.quicktype.io is the most powerful and complete UI. The web app also works offline and doesn't send your sample data over the Internet, so paste away!

For the best CLI, we recommend installing quicktype globally via npm:

npm install -g quicktype

Other options:

• Homebrew (infrequently updated)
• Xcode extension*
• VSCode extension*
• Visual Studio extension*

* limited functionality

Using quicktype

# Run quicktype without arguments for help and options
quicktype

# quicktype a simple JSON object in C#
echo '{ "name": "David" }' | quicktype -l csharp

# quicktype a top-level array and save as Go source
echo '[1, 2, 3]' | quicktype -o ints.go

# quicktype a sample JSON file in Swift
quicktype person.json -o Person.swift

# A verbose way to do the same thing
quicktype \
  --src person.json \
  --src-lang json \
  --lang swift \
  --top-level Person \
  --out Person.swift

# quicktype a directory of samples as a C++ program
# Suppose ./blockchain is a directory with files:
#   latest-block.json transactions.json marketcap.json
quicktype ./blockchain -o blockchain-api.cpp

# quicktype a live JSON API as a Java program
quicktype https://api.somewhere.com/data -o Data.java

Generating code from JSON schema

The recommended way to use quicktype is to generate a JSON schema from sample data, review and edit the schema, commit the schema to your project repo, then generate code from the schema as part of your build process:

# First, infer a JSON schema from a sample.
quicktype pokedex.json -l schema -o schema.json

# Review the schema, make changes,
# and commit it to your project repo.

# Finally, generate model code from schema in your
# build process for whatever languages you need:
quicktype -s schema schema.json -o src/ios/models.swift
quicktype -s schema schema.json -o src/android/Models.java
quicktype -s schema schema.json -o src/nodejs/Models.ts

# All of these models will serialize to and from the same
# JSON, so different programs in your stack can communicate
# seamlessly.

Generating code from TypeScript (Experimental)

You can achieve a similar result by writing or generating a TypeScript file, then quicktyping it. TypeScript is a typed superset of JavaScript with simple, succinct syntax for defining types:

interface Person {
  name: string;
  nickname?: string; // an optional property
  luckyNumber: number;
}

You can use TypeScript just like JSON schema was used in the last example:

# First, infer a TypeScript file from a sample (or just write one!)
quicktype pokedex.json -o pokedex.ts --just-types
# Review the TypeScript, make changes, etc.
quicktype pokedex.ts -o src/ios/models.swift

Calling quicktype from JavaScript

You can use quicktype as a JavaScript function within node or browsers. First add the quicktype-core package:

$ npm install @willh/quicktype-core

In general, first you create an InputData value with one or more JSON samples, JSON schemas, TypeScript sources, or other supported input types. Then you call quicktype, passing that InputData value and any options you want.

const {
  quicktype,
  InputData,
  jsonInputForTargetLanguage,
  JSONSchemaInput,
  FetchingJSONSchemaStore,
} = require("@willh/quicktype-core");

async function quicktypeJSON(targetLanguage, typeName, jsonString) {
  const jsonInput = jsonInputForTargetLanguage(targetLanguage);

  // We could add multiple samples for the same desired
  // type, or many sources for other types. Here we're
  // just making one type from one piece of sample JSON.
  await jsonInput.addSource({
    name: typeName,
    samples: [jsonString],
  });

  const inputData = new InputData();
  inputData.addInput(jsonInput);

  return await quicktype({
    inputData,
    lang: targetLanguage,
  });
}

async function quicktypeJSONSchema(targetLanguage, typeName, jsonSchemaString) {
  const schemaInput = new JSONSchemaInput(new FetchingJSONSchemaStore());

  // We could add multiple schemas for multiple types,
  // but here we're just making one type from JSON schema.
  await schemaInput.addSource({ name: typeName, schema: jsonSchemaString });

  const inputData = new InputData();
  inputData.addInput(schemaInput);

  return await quicktype({
    inputData,
    lang: targetLanguage,
  });
}

async function main() {
  const { lines: swiftPerson } = await quicktypeJSON(
    "swift",
    "Person",
    jsonString
  );
  console.log(swiftPerson.join("\n"));

  const { lines: pythonPerson } = await quicktypeJSONSchema(
    "python",
    "Person",
    jsonSchemaString
  );
  console.log(pythonPerson.join("\n"));
}

main();

The argument to quicktype is a complex object with many optional properties. Explore its definition to understand what options are allowed.

Contributing

quicktype is Open Source and we love contributors! In fact, we have a list of issues that are low-priority for us, but for which we'd happily accept contributions. Support for new target languages is also strongly desired. If you'd like to contribute, need help with anything at all, or would just like to talk things over, come join us on Slack.

Setup, Build, Run

quicktype is implemented in TypeScript and requires nodejs and npm to build and run.

First, install typescript globally via npm:

Clone this repo and do:

macOS / Linux

npm install
script/quicktype # rebuild (slow) and run (fast)

Windows

npm install --ignore-scripts # Install dependencies
npm install -g typescript # Install typescript globally
tsc --project src/cli # Rebuild
node dist\cli\index.js # Run

Edit

Install Visual Studio Code, open this workspace, and install the recommended extensions:

code . # opens in VS Code

Live-reloading for quick feedback

When working on an output language, you'll want to view generated output as you edit. Use npm start to watch for changes and recompile and rerun quicktype for live feedback. For example, if you're developing a new renderer for fortran, you could use the following command to rebuild and reinvoke quicktype as you implement your renderer:

npm start -- "--lang fortran pokedex.json"

The command in quotes is passed to quicktype, so you can render local .json files, URLs, or add other options.

Test

quicktype has many complex test dependencies:

• crystal compiler
• dotnetcore SDK
• Java, Maven
• elm tools
• g++ C++ compiler
• golang stack
• swift compiler
• clang and Objective-C Foundation (must be tested separately on macOS)
• rust tools
• pike interpreter
• Bundler for Ruby
• haskell stack

We've assembled all of these tools in a Docker container that you build and test within:

# Build and attach to Docker container
script/dev

# Run full test suite
npm run test

# Test a specific language (see test/languages.ts)
FIXTURE=golang npm test

# Test a single sample or directory
FIXTURE=swift npm test -- pokedex.json
FIXTURE=swift npm test -- test/inputs/json/samples