JSON to Go

How fields and types are inferred

Each nested object becomes its own exported struct, named after the key that holds it (address → Address). Keys inside an array are named from the singular form, so projects: [{…}, {…}] produces a single Project struct rather than one type per element.

Optional fields become omitempty

A key that appears in one element of an array but not in its siblings is optional. Optional and nullable fields get ,omitempty on the tag, which is what lets Go round-trip a payload where a field is simply absent:

type Project struct {
	ID       int64  `json:"id"`
	Title    string `json:"title"`
	Archived bool   `json:"archived,omitempty"`
}

Uncheck Add omitempty to optional fields if you want every key marshalled unconditionally — for instance when an API expects the field to always be present.

Nullable values and pointers

JSON has three states for a field: present with a value, present as null, and absent. A plain string can only represent the first two of these ambiguously. With Nullable scalars as pointers enabled, a value that was null in the sample becomes *string, so a nil pointer tells you the API explicitly said null. Slices and structs skip the pointer, since a nil slice already carries the same meaning.

Using the generated structs

var payload Root
if err := json.Unmarshal(body, &payload); err != nil {
	log.Fatal(err)
}
fmt.Println(payload.Address.City)

Edge cases worth knowing

• Method names beat tags on export. A key has to survive as an exported Go identifier, so it is converted to PascalCase: isActive becomes IsActive, and well-known initialisms are preserved (id → ID, url → URL). The original spelling always lives on in the json tag, so marshalling stays exact.
• Keys starting with a digit ("2fa") cannot be Go identifiers. They get a leading underscore and become unexported — the tag still works, but you may want to rename them by hand.
• Mixed arrays. [1, "two"] has no single Go type; the element becomes any.
• An empty array carries no element type, so it becomes []any. Uncheck Use any instead of interface{} if your module targets Go 1.17 or earlier.

FAQ