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`Schema.toStandardJSONSchemaV1` output has no `$schema`

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@gcanti is already working on this.

Since Oct 22, 2026.

  • #9772 by @MichaelDeBoey — open

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Description

What is the problem this feature would solve?

Schema.toStandardJSONSchemaV1 returns a schema without a root $schema for both supported targets ([email protected]):

import { Schema } from "effect"

const Point = Schema.Tuple([Schema.String, Schema.Boolean])
const { jsonSchema } = Schema.toStandardJSONSchemaV1(Point)["~standard"]

console.log(JSON.stringify(jsonSchema.input({ target: "draft-2020-12" })))
console.log(JSON.stringify(jsonSchema.input({ target: "draft-07" })))

{"type":"array","prefixItems":[{"type":"string"},{"type":"boolean"}],"maxItems":2,"minItems":2}
{"type":"array","maxItems":2,"minItems":2,"items":[{"type":"string"},{"type":"boolean"}]}

Code that receives one of these schemas later, such as a validator or a document generator that collects schemas from several libraries, can't tell from the schema itself which draft it is. That matters for keywords whose meaning changed between drafts: array-form items is a tuple in draft-07 but invalid in draft 2020-12, where prefixItems replaces it.

The other Standard JSON Schema implementations write $schema for both targets ([email protected], [email protected], [email protected] through toStandardJsonSchema from @valibot/[email protected], [email protected]), here for the same tuple:

arktype draft-2020-12 https://json-schema.org/draft/2020-12/schema
arktype draft-07 http://json-schema.org/draft-07/schema#
sury draft-2020-12 https://json-schema.org/draft/2020-12/schema
sury draft-07 http://json-schema.org/draft-07/schema#
valibot draft-2020-12 https://json-schema.org/draft/2020-12/schema
valibot draft-07 http://json-schema.org/draft-07/schema#
zod draft-2020-12 https://json-schema.org/draft/2020-12/schema
zod draft-07 http://json-schema.org/draft-07/schema#

Effect 3's JSONSchema.make writes it too ([email protected]):

import { JSONSchema, Schema } from "effect"

const Point = Schema.Tuple(Schema.String, Schema.Boolean)
console.log(JSON.stringify(JSONSchema.make(Point, { target: "jsonSchema7" })))
console.log(JSON.stringify(JSONSchema.make(Point, { target: "jsonSchema2020-12" })))

{"$schema":"http://json-schema.org/draft-07/schema#","type":"array","minItems":2,"items":[{"type":"string"},{"type":"boolean"}],"additionalItems":false}
{"$schema":"https://json-schema.org/draft/2020-12/schema","type":"array","minItems":2,"prefixItems":[{"type":"string"},{"type":"boolean"}],"items":false}

It does so in make:

https://github.com/Effect-TS/effect/blob/57b747f0cf4ddec47f23c08553c9e7011e31f8a4/packages/effect/src/JSONSchema.ts#L277-L281

In Effect 4, Schema.toJsonSchemaDocument keeps the draft in Document.dialect, so the information exists. It is lost in the Standard JSON Schema adapter, which returns only document.schema, in toBaseStandardJSONSchemaV1:

https://github.com/Effect-TS/effect/blob/110fd22e6555b86301d2e89997386b8c4b71fad3/packages/effect/src/internal/schema/standardSchema.ts#L96-L109

What is the feature you are proposing to solve the problem?

Set the root $schema in toBaseStandardJSONSchemaV1, using the URIs effect/JsonSchema already exports as META_SCHEMA_URI_DRAFT_07 and META_SCHEMA_URI_DRAFT_2020_12.

Setting it once on the draft 2020-12 schema may be enough, because JsonSchema.toDocumentDraft07 already rewrites a root draft 2020-12 $schema to the draft-07 URI in convertMetaSchemaKeyword:

import { JsonSchema, Schema } from "effect"

const doc = Schema.toJsonSchemaDocument(Schema.Tuple([Schema.String, Schema.Boolean]))
const withUri = { ...doc, schema: { $schema: JsonSchema.META_SCHEMA_URI_DRAFT_2020_12, ...doc.schema } }
console.log(JSON.stringify(JsonSchema.toDocumentDraft07(withUri).schema))

{"$schema":"http://json-schema.org/draft-07/schema#","type":"array","maxItems":2,"minItems":2,"items":[{"type":"string"},{"type":"boolean"}]}
What alternatives have you considered?

The caller of input / output knows which target it asked for and can add $schema itself. That only helps when the same code later reads the schema; once the schema is passed on, the target is gone.

The Standard JSON Schema spec doesn't require $schema, so this is a request for consistency with Effect 3 and the other implementations rather than a spec violation.

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