vercel.json schema declares draft-04 but uses draft-06+ keywords, so strict validators reject it #17639

The schema at https://openapi.vercel.sh/vercel.json declares draft-04 but uses keywords that do not exist in draft-04, so it fails validation against the metaschema it names. Tools that honour $schema reject the document rather than applying it.

Reproduce

curl -sO https://openapi.vercel.sh/vercel.json

import json, jsonschema
s = json.load(open("vercel.json"))
print(s["$schema"])                      # http://json-schema.org/draft-04/schema#
jsonschema.Draft4Validator.check_schema(s)

jsonschema.exceptions.SchemaError: {'type': 'object', 'additionalProperties': False,
 'required': ['root'], 'properties': {'root': {'description': 'Path to the servic...

Behaviour across metaschemas (jsonschema 4.26.0), same file, unchanged:

Keywords that force this

Counting occurrences in the served file:

exclusiveMinimum is the one worth pausing on: in draft-04 it is a boolean modifier on minimum; from draft-06 it is a number. It is not merely unrecognised here, it means something different.

Why it matters

Editors resolve this URL from $schema and from schema catalogues, and apply it while you type. A strict loader refuses the whole document at that point, which means no completion and no diagnostics — a config file with a typo looks exactly like a config file without one. Ajv in strictSchema mode is in the same position, and so is every Go/Java/Rust validator that reads $schema to pick its dialect.

Two things make this easy to miss from the inside: the file is consumed by Vercel's own tooling through a purpose-built reader (packages/config/scripts/generate-types.ts parses it by hand for code generation) rather than a general validator, and Vercel's TypeScript reader already assumes the newer keywords.

Suggested fix

Change the dialect declaration to the one the content already uses:

-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",

No other change is required. draft-07 accepts everything currently in the file, and it accepts the $data references only as opaque annotations, which is the same treatment they receive today. If the intent is to keep $data functional, note that it is an Ajv extension rather than a spec keyword, so a $comment saying so would help other consumers.

How this came up

I wrote a small mutation tester for validators — it feeds a validator inputs that ought to be rejected and reports what it lets through. Pointing it at served JSON schemas surfaced this one as a special case: the schema does not merely accept something it should reject, it cannot load at all under the dialect it names. The tool is https://github.com/simin-yuan/greencheck (MIT, no dependencies); the reproduction above stands on its own without it.