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A JSON generator without a template language

Template-based generators ask you to learn a small language. This asks you to name your fields and pick their types. Each approach buys something the other does not.

Template language versus typed fields

A template generator hands you the whole JSON document and a placeholder syntax to fill it: you write the structure literally, with expressions where the values go. The structure is therefore anything you can type — arrays of arrays, objects whose keys differ per branch, values computed from a loop index.

A schema builder inverts that. You declare typed fields and the tool assembles records from them. You give up arbitrary structure and get three things back: the shape is data rather than a string, so it can be shared as a link, saved, diffed and re-exported in six other formats; every field carries a real type, so the same schema can emit a TypeScript interface or a CREATE TABLE; and there is nothing to learn before the first row appears.

Nesting without a template

The one structural thing most people actually need from a template is nesting, and that does not require one. A field named with dots becomes a nested object: 

Fields:  id, user.name, user.email, address.city

{
  "id": 1,
  "user":    { "name": "Ada", "email": "ada@example.test" },
  "address": { "city": "Kyoto" }
}

Nesting goes as deep as the dots do. What it will not produce is an array of nested objects of varying length inside each record — that is where a template is genuinely the better tool.

Side by side

Describing a shape as fields, or as a template
 Fun Data Playgrounda template-based JSON generator
How you describe the shapeTyped fields in a builderA JSON document with placeholder expressions
What you have to learn firstNothingA small template syntax
What the shape itself isData — shareable as a link, saved, diffedA string you author
Nested objectsDot-notation field names (user.email)Written out literally
Arrays of varying length inside a recordNot supportedSupported
Other outputs from the same shapeCSV, TSV, SQL, XML, TypeScript, Zod, PydanticUsually JSON only

Structural differences only — how each tool is used, not what it currently offers. Check the other tool's own documentation before deciding.

Where a template generator is the better answer

  • Arrays inside records — an order with a variable number of line items, a post with a list of comments.
  • Structure that varies between records, where different branches have different keys.
  • Values computed across the document, rather than per field.
  • A document you already have that you want to keep verbatim and only substitute values into.

Tools change. This page sticks to structural differences — how each one is used rather than what it currently offers — but check the current documentation of whichever you are comparing rather than trusting any comparison page, including this one.

Where a schema wins

  • Six formats from one definition. The same schema exports JSON, NDJSON, CSV, TSV, SQL, XML and a real spreadsheet — a template describes one document shape.
  • The schema is shareable and reviewable. It encodes into a link, so a colleague opens the exact setup rather than pasting a template.
  • Typed fields produce typed output. Numbers are numbers and booleans are booleans in JSON, and the same field types produce a matching SQL column type or code declaration.
  • Nothing to learn. The failure mode of a template DSL is a syntax error in a language you use twice a year.

Typed values, not stringly-typed ones

A common frustration with template output is that everything arrives as a string, because the template is text and the substitution is textual. Here the field type decides the JSON type: an Integer field emits 42, a Boolean emits true, and a field with a blank percentage emits null rather than "". That matters the moment the fixture meets a validator — which is exactly what a generated Zod schema or JSON Schema will do to it.

Common questions

Can it produce nested JSON?

Yes. A field named with dots becomes a nested object — user.name and user.email produce a user object with two keys — and nesting goes as deep as the dots do.

Can it produce an array inside each record?

No. A variable-length array of nested objects per record is the case where a template generator is genuinely the better tool.

Are numbers and booleans real JSON types?

Yes. The field type decides the JSON type, so an Integer field emits 42 rather than "42", a Boolean emits true, and a field with a blank percentage emits null rather than an empty string.

Do I have to learn a syntax?

No. You name fields and pick types from a list. The two places syntax appears are optional: a pattern field for shaped identifiers, and a formula field for values derived from other fields.

Can I share the setup with a colleague?

Yes — the schema encodes into the URL, so a link opens the exact setup. Signed in, you can also save named schemas and create revocable share links.

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