JSON to Elm Converter

Working with JSON data and need Elm models fast? JSON is natively parsed by all major runtimes — no schema required to begin parsing. This free, browser-based converter parses your JSON and generates clean, production-ready Elm code — no account required.

How to use this converter

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

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

The problem with manual JSON-to-Elm mapping

Elm is a purely functional, strongly typed language — typed data models are central to how it works. Yet copying fields from JSON payloads into Elm type alias / type 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

Elm decoders are composable and explicit — this converter generates type-safe Decoder pipelines that handle missing fields gracefully.

This converter eliminates the manual step entirely.

Elm and JSON: what you need to know

Elm is a purely functional, strongly typed language, used for reliable frontend applications with no runtime exceptions. It uses record and custom type based with elm/json decoders for structured data — making it a natural fit for JSON-driven applications.

What the converter generates

The output consists of Elm type alias records with explicit Decoder definitions. This is the idiomatic pattern for Elm data models, compatible with popular Elm serialization libraries.

A common gotcha

Elm decoders must be explicitly composed — any missing field decoder causes a compile error, not a runtime crash.

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

• Keeping Elm structs in sync when JSON schemas evolve
• Onboarding new team members by auto-generating the data layer
• Validating JSON contract compatibility with Elm type definitions
• Generating Elm models from reliable SPAs API responses
• Creating typed DTOs for data-driven frontends
• Rapid prototyping with real JSON payloads

Frequently asked questions

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 Elm model.

What serialization library does the generated Elm code assume?

The generated code is compatible with the standard Elm serialization ecosystem — Elm type alias records with explicit Decoder definitions. No unusual dependencies required.

What version of Elm does the output target?

The converter targets modern Elm conventions — Elm type alias records with explicit Decoder definitions. 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.

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 Elm, bookmark this page to skip the manual model-writing step entirely.