feat(standard-json-openapi): add package for Standard JSON Schema OpenAPI

[gusanthiago]

Hey everyone, this supersedes #2042 based on the review there, and should close #1763.

Summary

@hono/zod-openapi takes Zod and nothing else today. This new package, @hono/standard-json-openapi, takes schemas from any library implementing Standard JSON Schema — ArkType, Valibot once wrapped with toStandardJsonSchema(), and Zod 4, which ships it natively. A route can mix them.

import { OpenAPIHono, createRoute } from '@hono/standard-json-openapi'
import { type } from 'arktype'

const app = new OpenAPIHono()

app.openapi(
  createRoute({
    method: 'post',
    path: '/users',
    request: {
      body: {
        required: true,
        content: { 'application/json': { schema: type({ name: 'string' }) } },
      },
    },
    responses: { 200: { description: 'Created' } },
  }),
  (c) => c.json({ name: c.req.valid('json').name }, 200)
)

Solution

@asteasolutions/zod-to-openapi reads Zod internals, so a foreign schema cannot go to it directly. Non-Zod schemas are hidden inside a Zod carrier (z.string().openapi(jsonSchema)) — the generator merges .openapi() metadata over whatever it generated, so the output comes entirely from ~standard.jsonSchema. Zod schemas are never converted and behave exactly as before.

Test

pnpm test in packages/standard-json-openapi — 18 pass. They cover ArkType and mixed routes: validation, parameters, input vs output, response headers and sub-apps.

The author should do the following, if applicable

• Add tests
• Run tests
• pnpm changeset at the top of this repo and push the changeset
• Follow the contribution guide

[changeset-bot]

🦋 Changeset detected

Latest commit: 981c521

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hono/standard-json-openapi	Minor

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[KTrain5169]

Please just don't try and force Zod into the package here

[gusanthiago]

Hey @KTrain5169, thanks for the review

• I dropped Zod as a runtime dependency so we can decouple that part;
• Simplified some logic around the module to avoid excessive implementations;
• Adjusted other points about README.md.

Let me know if it is okay now

[KTrain5169]

I haven't been able to take a proper look at the code myself yet as I don't really have time to experiment to the level required to have a thorough code review

[KTrain5169]

Any reason why this is the case?

[gusanthiago]

No reason; that was gap — the array never reached a validator, so nothing was validated. Now each schema validates. Only the typing stays limited, since Hono has a single header target. Adjusted the Limitation and added a test.

[KTrain5169]

@yusukebe Should middlewares be published as ESM-only?

[gusanthiago]

@KTrain5169

I did adjustments mentioned in the PR. Let me know if I need to work on anything more.

Thanks for the review