JSON to Flow Converter

JSON is a lightweight, human-readable key-value format — widely used for REST API responses, configuration files, NoSQL documents. Converting it to strongly-typed Flow structures eliminates runtime surprises and speeds up development. This tool does it in one click, entirely in your browser.

How to use this converter

1. Paste your JSON into the left editor panel
2. Click Generate
3. Copy the generated Flow code from the right panel

No account. No upload. No tracking. Runs entirely in your browser.

The problem with manual JSON-to-Flow mapping

Flow is a gradual static typing for JavaScript language — typed data models are central to how it works. Yet copying fields from JSON payloads into Flow type / interface definitions introduces subtle errors:

• Mistyped field names cause silent deserialization failures
• Missing optional fields trigger runtime panics or null errors
• Schema drift between API and model goes undetected until production

Flow uses structural typing with exact object types ({| |}) to catch unexpected property access at compile time.

This converter eliminates the manual step entirely.

Flow and JSON: what you need to know

Flow is a gradual static typing for JavaScript language, used in Meta/Facebook codebases and React Native projects. It uses type alias and object type based for structured data — making it a natural fit for JSON-driven applications.

What the converter generates

The output consists of Flow type definitions with exact object types and nullable annotations. This is the idiomatic pattern for Flow data models, compatible with popular Flow serialization libraries.

A common gotcha

Flow's ?Type (nullable) differs from TypeScript's Type | null | undefined — make sure your runtime handles both null and undefined.

JSON input characteristics

JSON supports nested objects, arrays, strings, numbers, booleans, and null. Tools like jq, Postman, and browser DevTools make JSON the most developer-friendly data exchange format.

Common use cases

• Validating JSON contract compatibility with Flow type definitions
• Generating Flow models from React Native codebases API responses
• Creating typed DTOs for Meta-ecosystem JavaScript
• Rapid prototyping with real JSON payloads
• Keeping Flow structs in sync when JSON schemas evolve
• Onboarding new team members by auto-generating the data layer

Frequently asked questions

What serialization library does the generated Flow code assume?

The generated code is compatible with the standard Flow serialization ecosystem — Flow type definitions with exact object types and nullable annotations. No unusual dependencies required.

What version of Flow does the output target?

The converter targets modern Flow conventions — Flow type definitions with exact object types and nullable annotations. If you need output for an older version, the generated code can typically be adapted with minor changes.

Is my JSON data sent to a server?

No. All conversion runs locally in your browser using client-side JavaScript. Your JSON data never leaves your machine.

What JSON inputs does this converter accept?

Paste any valid JSON — including REST API responses, configuration files, NoSQL documents. The converter infers types and generates a matching Flow model.

Related tools on LangStop

• JSON Formatter & Validator — https://langstop.com/json-formatter
• JSON to Python Converter — https://langstop.com/json-to-python
• JSON to Go Converter — https://langstop.com/json-to-go
• JSON to Java Converter — https://langstop.com/json-to-java
• JSON to JSON Schema — https://langstop.com/json-to-json-schema

If you work frequently with JSON and Flow, bookmark this page to skip the manual model-writing step entirely.