Given JSON object, get its schema definition

[rsinohara]

Hi, I am just starting with zod, looks amazing.

The one tool I am missing and would dearly need is something that can generate a schema from a given json object. Doesn't have to be extra smart (but some intelligence would be great).

Is there any such tool around? I will eventually be using this so much that it might save time if I have to do a rudimentary one.

To be clear, I don't need that dynamically, just static conversion to get started on the schema.

[scotttrinh]

Are you picturing a command-line tool that outputs a Zod schema given some arbitrary JSON input?

$ cat input.json
{
  "a": "a string",
  "b": 42,
  "c": true,
  "d": null,
  "xs": ["x", "y", "z"]
}
$ cat input.json | some-zod-cli-tool
z.object({
  a: z.string(),
  b: z.number(),
  c: z.boolean(),
  d: z.null(),
  xs: z.array(z.string()),
});

Something like that? I'm not aware of anything like that, but there are projects output JSON schemas so perhaps you could use something like https://github.com/StefanTerdell/zod-to-json-schema as inspiration for making such a tool?

[StefanTerdell]

Here you go :)

import { format } from "prettier";

const jsonToZod = (obj: any): string => {
  const parse = (obj: any): string => {
    switch (typeof obj) {
      case "string":
        return "z.string()";
      case "number":
        return "z.number()";
      case "bigint":
        return "z.number().int()";
      case "boolean":
        return "z.boolean()";
      case "object":
        if (Array.isArray(obj)) {
          const options = obj
            .map(parse)
            .reduce(
              (acc, curr) => (acc.includes(curr) ? acc : [...acc, curr]),
              []
            );
          if (options.length === 1) {
            return `z.array(${options[0]})`;
          } else if (options.length > 1) {
            return `z.array(z.union([${options}]))`;
          } else {
            return "z.array(z.unknown())";
          }
        }

        return `z.object({${Object.entries(obj)
          .map(([k, v]) => `${k}:${parse(v)}`)
          }})`;
      case "undefined":
        return "z.undefined()";
      case "function":
        return "z.function()";
      case "symbol":
      default:
        return "z.unknown()";
    }
  };

  return format(`const schema=${parse(obj)}`, { parser: "babel" });
};

[StefanTerdell]

Clone and run locally :)

https://github.com/StefanTerdell/json-to-zod-react

[StefanTerdell]

Probably too lazy to maintain it though. Let me know if I should transfer the repos/npm package rights to you and you can go from there.

[StefanTerdell]

Turns out Github Pages is insanely easy to work with :D

https://stefanterdell.github.io/json-to-zod-react/

[rsinohara]

Yes, it's incredibly easy, that's what I was going for :)

[rsinohara]

Amazing!!

[StefanTerdell]

Reposting my answer so it doesn't get buried in the thread

Here's a page where you can paste your JSON or JS objects (JSON5)

Or if you prefer a package/CLI

If anyone wants to maintain it, let me know and I'll transfer the repos.

[edit: borken link]

[StefanTerdell]

@rsinohara Nah, I'll transfer them completely. I have no use for them so it's better you own them. Just one thing, you have to delete your fork before I can transfer the package repo to you. You should already have gotten the website repo, though.

[rsinohara]

@StefanTerdell fork deleted. I got the mail for the page repo, but it expired before I could use the link.

[StefanTerdell]

@rsinohara Ok, I'll try and send both again now

[rsinohara]

Got them. I just need to put github page up again. Thanks for the work! I'll add you, if not already there.

[StefanTerdell]

Cool! Looks online to me https://rsinohara.github.io/json-to-zod-react/

You might want to PR the URL change to the Zod repo.

npm run deploy to update it.

GLHF! :)