Schemato

Browser-only schema converter for JSON, JSON Schema, OpenAPI, GraphQL, SQL DDL, Protobuf, Prisma, Mongoose, Avro, and TypeScript.

Live: https://www.schemato.top

Schemato turns 10 input formats into typed code for 15 target languages. It is built for developers who need a quick type, validator, or DTO from a sample payload or schema without installing a CLI or uploading data to an API.

• 149 live converter pages generated from one format registry
• Multi-sample JSON inference: paste NDJSON samples to capture optional fields
• 100% client-side conversion: pasted payloads stay in the browser
• No signup, no backend, no API cost
• Open source under the MIT license

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Quick examples

Need	Try
Runtime validation for a JSON API response	JSON -> Zod
FastAPI models from a JSON Schema	JSON Schema -> Pydantic
TypeScript interfaces from GraphQL SDL	GraphQL -> TypeScript
Go DTOs from SQL DDL	SQL DDL -> Go struct
Compare with quicktype	Schemato vs quicktype

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Supported formats

Inputs

Input format	Status	Notes
JSON	Live	Infers a shared Shape from one sample, arrays, or NDJSON samples
JSON Schema	Live	Supports common object, array, enum, and primitive schema shapes
OpenAPI 3.x	Live	Reads schema objects from JSON or YAML-like specs
GraphQL SDL	Live	Parses object types into typed output models
SQL DDL	Live	Covers a practical Postgres / MySQL / SQLite subset
Protobuf	Live	Parses message fields
Prisma schema	Live	Parses model blocks
Mongoose schema	Live	Parses new Schema({...})-style definitions
Avro	Live	Parses records, enums, arrays, maps, and unions
TypeScript interfaces	Live	Converts TypeScript shapes into other targets

Outputs

TypeScript, Zod, Pydantic, Go struct, Rust struct, Swift, Kotlin, Java, C#, Dart, PHP, Ruby, Yup, Joi, and Python dataclass.

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Why?

I work across TypeScript, Go, and Python and got tired of:

• Writing types by hand for every new API response
• Tools that only support one or two output languages
• Tools that require installing something or paying a subscription
• Existing options that don't cover Zod, Pydantic, or modern serde-friendly Rust

Schemato fills the gap. One page per conversion, 149 statically generated converter pages, zero backend.

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What makes it different?

• One converter matrix, not one-off tools: the parser -> Shape -> renderer architecture keeps the project extensible.
• Practical defaults: optional fields from multi-sample JSON, json tags for Go, serde derives for Rust, Codable for Swift, validation-first output for Zod and Pydantic.
• Static and cheap to host: every converter page is generated at build time with output: "export".
• Privacy-friendly by design: conversion logic runs in the browser; there is no conversion API receiving pasted schemas.
• Easy to extend: one new parser unlocks all output languages; one new renderer unlocks all input formats.

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Tech stack

Next.js 16 (App Router) + TypeScript + TailwindCSS
output: "export" → fully static, deploys anywhere
Custom JSON-shape inferrer (~150 LOC, no quicktype dependency)
Input parsers → shared Shape model → per-language renderers

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Architecture

Instead of writing one adapter per conversion pair, Schemato uses a small intermediate Shape model:

flowchart LR
  A["Input text<br/>JSON / OpenAPI / GraphQL / SQL / ..."] --> B["Parser<br/>one per input format"]
  B --> C["Shape<br/>small shared contract"]
  C --> D["Renderer<br/>one per output language"]
  D --> E["Generated code<br/>Zod / Pydantic / Go / Rust / ..."]

Loading

That keeps the project linear:

• New input format: write one parser, get every output language.
• New output language: write one renderer, get every input format.
• New converter page: generated automatically from the format registry.

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Project layout

app/
  layout.tsx              # global header/footer
  page.tsx                # homepage with the matrix
  [slug]/page.tsx         # dynamic route /<from-slug>-to-<to-slug>
  sitemap.ts              # sitemap.xml generator
  robots.ts
components/
  ConverterShell.tsx      # left input / right output UI (client)
lib/
  formats.ts              # 24 format registry (slug, sample, blurb)
  url.ts
  site.ts
  seo-copy.ts             # per-pair SEO copy generator
  converters/
    index.ts              # registry + bridge (parser → renderer)
    json-shape.ts         # internal Shape type + JSON inferrer
    *-shape.ts            # input parsers → Shape
    renderers.ts          # all 15 language renderers (Shape → code)
    json-to-*.ts          # custom JSON adapters (one per language)

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Run locally

npm install
npm run dev          # http://localhost:3000
npm run build        # generates the static export in out/

Privacy

Conversions run in the browser. Schemato does not upload pasted schemas or payloads to a conversion API.

The site uses aggregate analytics to understand product usage, but conversion input and generated output are not sent as analytics event data.

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For directory and awesome-list maintainers

• Category: developer tool, schema converter, code generator, typed API tooling
• License: MIT
• Pricing: free
• Source: open source on GitHub
• Account required: no
• Hosted demo: https://www.schemato.top
• Primary use cases: JSON -> Zod, JSON Schema -> Pydantic, OpenAPI -> TypeScript, SQL DDL -> Go struct, multi-format schema conversion
• Privacy posture: browser-only conversion; pasted schemas are not sent to a conversion API

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Useful links

• Live site: https://www.schemato.top
• Changelog: https://www.schemato.top/changelog
• Guides: https://www.schemato.top/guides
• Privacy: https://www.schemato.top/privacy
• Security: https://github.com/weitaishan/schemato/blob/main/SECURITY.md
• Issues: https://github.com/weitaishan/schemato/issues

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How to add a new input format

1. Create lib/converters/<name>-shape.ts exporting:

   export function nameToShape(input: string, rootName?: string):
     | { ok: true; shape: Shape }
     | { ok: false; error: string }

2. In lib/converters/index.ts:

   import { nameToShape } from "./name-shape";
   for (const t of ALL_TARGETS) {
     register("name", t, bridge(nameToShape, t));
   }

3. Make sure lib/formats.ts has the format registered with a slug + sample.

That's it — 15 new pages light up automatically.

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How to add a new output language

1. Open lib/converters/renderers.ts

2. Add function fooType(shape: Shape): string and export const renderFoo: Renderer = (root, rootName) => { ... }

3. Register it in RENDERERS:

   export const RENDERERS = {
     ...,
     foo: renderFoo,
   };

4. Add foo to OUTPUT_FORMATS in lib/formats.ts with a slug + sample.

All input formats now produce the new output for free.

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Roadmap

• JSON input → 15 outputs
• NDJSON / multi-sample JSON inference for optional fields
• JSON Schema input → 15 outputs
• OpenAPI 3.x input → 15 outputs
• GraphQL SDL input → 15 outputs
• SQL DDL input → 15 outputs
• Protobuf input → 15 outputs
• Prisma schema input → 15 outputs
• Mongoose schema input → 15 outputs
• Avro input → 15 outputs
• TypeScript input → 14 outputs
• Discriminated union output for oneOf JSON Schema
• CLI version (npx schemato json-to-zod < schema.json)
• VS Code extension

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Contributing

PRs welcome. The project is small and the architecture rewards adding one renderer / parser at a time:

• Want Elixir / Scala / Haskell as an output language? Add a renderer.
• Want another schema language as input? Add a parser.
• Found an incorrect conversion? Open a bug report with a reduced input sample.
• Want a new converter pair prioritized? Open a converter request.

Each adapter is independent; nothing else needs to change.

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License

MIT