schemify-cli

Build JSON Schemas interactively, and fill JSON data from them, from the command line.

Source: github.com/aaltatan/schemify-cli

A web version runs at schemify.surge.sh (source): the same questions as fields, with the schema updating as you type.

Install

uv tool install schemify-cli

Usage

schemify generate -t Person -o person.schema.json   # ask for the properties, write the schema
schemify fill person.schema.json -o person.json     # ask for one object matching it
schemify list person.schema.json -f python          # ask for a list of them

generate: a Person with a full_name computed by joining first and last

fill: one object, full_name is computed, not asked

list: several objects, printed as Python

• -o, --output saves to a file (asks before overwriting); without it the result is printed.
• -f, --format picks the output of fill and list: json, python or javascript.

Types: string, integer, number, boolean, date, datetime, enum, array, object, each with its constraints (length, pattern, format, range, items, ...) and an optional default.

Computed properties

A property with x-compute is not asked in fill, it is computed from the other values:

"full_name": {"type": "string", "x-compute": {"fn": "join", "from": ["first", "middle?", "last"]}}

• fn: the computer, from: source paths (a list, or an {alias: path} object for template and expr), options: extra arguments, default: the value when a source is missing.
• Paths are relative to the owning object (address.city, items[0]), or to the root ($.company). items[*].price gives every price; a trailing ? makes a source optional.

Built-in computers:

• Text: join, concat, template, upper, lower, title, capitalize, trim, replace, slice, initials, slug, length, pad, mask
• Numbers: sum, subtract, multiply, divide, average, min, max, abs, round, percent, percent_of, expr
• Dates: today, now, add_days, add_months, add_years, days_between, age, year, month, day, weekday, format_date, start_of_month, end_of_month (a date left out or missing with ? is today, computed each run)
• Number to words: words (options: lang, prefix, suffix)
• Logic, lookup and misc: coalesce, if_else, equals, lookup, constant, count, count_if, unique, uuid

Reusing it in a typer app

schemify.cli.dependencies.schema exposes typer-di dependencies that load a schema file and ask for its data: FilledDataArgumentDI and FilledListArgumentDI take the path as an argument, FilledDataOptionDI and FilledListOptionDI as --js. When the path is optional or comes from elsewhere, call load_schema(path) and ask_or_abort(schema, ask_data) directly: both report failures as typer errors.

Development

uv sync
uv run pytest
uv run ruff check . && uv run mypy src

The demo GIFs are recorded with VHS (scoop install vhs or brew install vhs) and PowerShell (pwsh), from the repository root, generate first since the others use its schema:

vhs docs/demo/generate.tape && vhs docs/demo/fill.tape && vhs docs/demo/list.tape

After changing generators.py, validators.py or computers.py, run pnpm sync && pnpm check in the schemify editor so it stays in step.