JSON Schema Helper

A lightweight VS Code extension that validates JSON/JSONC files against a local JSON Schema and shows diagnostics (warnings) directly in the editor.

It can resolve a schema in two ways:

Per-file via $schema at the root of the JSON document
Via workspace mappings (glob → schema path), useful when files don’t embed $schema

This is designed for projects that keep schemas in-repo (e.g. ./schemas/*.schema.json) and want quick feedback without setting up a full schema association system.

Features

✅ Validate JSON and JSONC (comments + trailing commas supported)
✅ Uses local JSON Schema files (relative or absolute paths)
✅ Diagnostics for:
- Unknown properties (not in schema)
- Missing required properties
- Type mismatches (string, number, integer, boolean, object, array, null)
✅ Supports:
- $ref pointers (#/...)
- allOf merging
- oneOf / anyOf (currently validates using the first option)
✅ Schema caching (reloads automatically when schema file changes)

Quick start

1) Add `$schema` to your JSON

Given this schema:

schemas/user.schema.json

{
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "age": { "type": "number" },
    "tags": { "type": "array", "items": { "type": "string" } },
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "zip": { "type": "string" }
      },
      "required": ["street"]
    }
  },
  "required": ["name"]
}

Use it from a JSON file:

test.json

{
  "$schema": "./schemas/user.schema.json",
  "name": "Ada",
  "age": 30,
  "size": "medium"
}

You’ll get a warning like:

Unknown property "size" (not in schema).

Workspace schema mappings (recommended for larger projects)

Instead of adding $schema everywhere, you can map files to schemas in your VS Code settings.

Example: associate every *.user.json file with schemas/user.schema.json.

.vscode/settings.json

{
  "jsonSchemaHelper.schemaMappings": [
    {
      "pattern": "**/*.user.json",
      "schemaPath": "schemas/user.schema.json"
    }
  ]
}

How paths are resolved

schemaPath in mappings is resolved from the workspace folder
$schema values are resolved relative to the JSON document (unless absolute)
Absolute paths are supported
file://... URIs are supported
Remote schemas (http://, https://, etc.) are ignored (no network requests)

Extension settings