GoTyper

Generate Go structs from JSON samples or JSON Schema. GoTyper reads files, stdin, or URLs and writes formatted Go code with JSON tags. Configuration adds YAML/XML tags, field naming, type mappings, and validation tags.

Install

With Go 1.27 or later:

go install github.com/mcncl/gotyper@latest

Or download a binary from GitHub releases.

Quick start

echo '{"id": 1, "name": "Ada"}' | gotyper -r User -p models

Output:

// Code generated by gotyper. DO NOT EDIT.

package models

type User struct {
	Id   int64  `json:"id"`
	Name string `json:"name"`
}

Usage

# Read a file and write Go code
gotyper -i user.json -o user_generated.go -p models -r User

# Fetch JSON from an API
gotyper --url https://api.github.com/users/octocat -r GitHubUser

# Merge multiple samples into one model
gotyper --sample first.json --sample second.json -r Response -o response.go

# Read newline-delimited JSON
gotyper --ndjson -i responses.ndjson -r Response

# Generate from JSON Schema instead of samples
gotyper --schema user.schema.json -p models -r User

Run gotyper without arguments to paste JSON interactively. Finish with Ctrl+D on Unix/macOS, or Ctrl+Z followed by Enter on Windows. Run gotyper --help for all flags and defaults.

Each ordinary input contains one JSON value. Use repeated --sample flags for multiple files, or --ndjson for one value per nonblank line. --sample cannot be combined with --input, --url, --schema, or --interactive; --ndjson cannot be combined with --schema.

How types are inferred

• Object samples merge their fields, including objects inside arrays.
• Integers use int64; decimal/exponent numbers and integers outside that range use float64. Mixed numeric samples use float64.
• Missing or null fields use pointers by default. Incompatible types fall back to interface{}.
• Valid RFC3339 timestamps use time.Time. Other date strings and UUIDs stay strings.

See the reference for merging rules, nullable arrays, date handling, and the supported JSON Schema subset. Schema validation tags are metadata for a separate validator, not checks performed by encoding/json.

Configuration

Save a .gotyper.yml in your project directory:

package: models
root_name: User

naming:
  field_mappings:
    id: ID

json_tags:
  additional_tags: [yaml, xml]

GoTyper searches the current directory and its parents for .gotyper.yml, .gotyper.yaml, gotyper.yml, or gotyper.yaml. Select another file with --config path/to/config.yml.

Explicit --package, --root-name, and --format flags override configuration, even when set to CLI defaults. Unknown keys and unsupported settings return errors.

See the example configuration for supported settings, and the configuration reference for matching rules and legacy compatibility.

Repeatable generation and CI

Commit your input and configuration alongside the generated file. Install the same GoTyper version and Go toolchain locally and in CI, with gotyper on PATH.

For a models directory containing user.json, add generate.go:

package models

//go:generate gotyper --input user.json --output user_generated.go --package models --root-name User

Run go generate ./models from the project root. Paths in the directive are relative to the package directory. Unchanged input, options, configuration, and toolchain produce identical output, with no timestamps.

In CI, run the same command from the models directory with --check:

gotyper --input user.json --output user_generated.go --package models --root-name User --check

--check requires --output. It compares the full file byte for byte without writing files or generated code to stdout. It exits 0 when current and 1 when stale, missing, or unreadable. Rerun without --check to update the file.

Contributing

See CONTRIBUTING.md for development and testing instructions.

License

MIT