How to Convert JSON to TypeScript, Go, Java & More (Free, 2026 Guide)

Turn any JSON sample into TypeScript interfaces, Go structs, Java POJOs, Python dataclasses, Kotlin data classes, C# classes or Rust serde structs — free in your browser, nothing uploaded. Plus how the converters handle nested objects, mixed-shape arrays, and optional vs. nullable fields.

By ToolkitLife Team·October 11, 2026·

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Why Convert JSON to Code?

Every API integration starts with the same chore: a JSON response lands in your lap and you need typed structures around it. Hand-writing them is slow and error-prone — miss one field and your compiler or runtime finds out at the worst possible time. And when the API evolves, hand-maintained models drift from reality.

A converter solves both problems: it reads the actual sample you give it and emits idiomatic type declarations for your language, so your models match real payloads from day one and can be regenerated whenever the API changes.

What a Good Converter Detects

Nested objects become named types. A user.address.city structure produces a separate Address type instead of one unreadable inline blob, and shared shapes are reused by name.

Arrays merge their shapes. Real-world arrays are messy: not every object carries every key. A good converter unions the keys across all items and marks fields that are missing in some entries as optional — so your types stay honest about what the API actually returns.

Optional vs. nullable are kept apart. A key that is sometimes absent is not the same as a key that is present but null. These map to different constructs in every language (? vs. T | null in TypeScript, pointers vs. zero values in Go, Option<T> in Rust), and the generated code preserves the distinction.

Depth is bounded. Pathologically deep JSON produces unreadable output, so generation stops at a sane depth and falls back to generic maps — a deliberate trade of completeness for usability.

Pick Your Language

All seven converters share the same inference engine, so the same sample produces consistent output everywhere:

TypeScript — nested interfaces, ? for optional fields, union types for nullables. Strict-mode friendly: JSON to TypeScript.
Go — structs with json tags, pointers for nullable fields so unmarshal can represent "absent": JSON to Go struct.
Java — POJOs with getters and setters, ready for Jackson or Gson: JSON to Java POJO.
Python — @dataclass definitions with type hints: JSON to Python dataclass.
Kotlin — data classes with nullable types as T?: JSON to Kotlin data class.
C# — property classes for System.Text.Json or Newtonsoft: JSON to C# class.
Rust — serde-compatible structs with Option<T>: JSON to Rust serde struct.

JSON to TypeScript Converter

Paste a JSON sample, get nested TypeScript interfaces with optional and nullable fields handled correctly. Runs entirely in your browser — free and private.

Try JSON to TypeScript Converter →

Convert in Three Steps

1. Paste a representative sample. The output is only as accurate as the input: include the items with missing fields, the nulls, the nested lists — not just the happy path.

2. Name the root type. Rename Root to something meaningful (User, OrderResponse) before copying; nested types are named automatically from their keys.

3. Copy and review. Scan the optional and nullable markers first — they are where converters and APIs disagree most — then paste into your project.

Tips for Cleaner Generated Types

Feed it the weird cases. If one array item lacks a field, convert a sample that includes that item — otherwise the field comes out required and your parser will crash on it later.

Regenerate when the API changes. Treat the generated types as build artifacts: cheap to recreate, never hand-edited.

Deeply nested payloads: consider maps. If the API returns an arbitrary-keyed dictionary, a generated Record<string, T>-style map is more honest than twenty one-shot interfaces.

Nothing leaves your machine. Every converter on ToolkitLife parses and generates inside your browser tab. That matters when the JSON contains customer data, tokens, or anything confidential — there is no server to leak it to.

FAQ

Is it safe to paste API responses or customer data into a JSON converter?+

Yes, when the tool runs entirely client-side. ToolkitLife's converters parse the JSON and generate code inside your browser tab with no network requests and no storage, so sensitive payloads never leave your machine.

How are arrays with inconsistent fields handled?+

The converter merges the shapes of all objects in an array: it takes the union of keys and marks any field that is missing from some items as optional, so the generated type reflects what the API actually returns.

What is the difference between optional and nullable fields?+

Optional means the key may be absent entirely; nullable means the key is present but can be null. They map to different constructs — e.g. ? versus T | null in TypeScript, pointers versus zero values in Go, Option<T> in Rust — and the converter preserves the distinction.

Is there a size or depth limit for the input JSON?+

Large samples of several megabytes are fine because parsing happens locally. Extremely deep nesting is capped at a fixed depth: generation falls back to generic map types there to keep the output readable.