4.6JSON Schema

Type: json_schema. Checks: the whole JSON response against a JSON Schema. A JSON Schema is a standard way to describe JSON data: which fields it has, what type each one is, and which are required. It catches a renamed field, a number that became text, or a missing field. It works on URL, API and multi-step API monitors only. On other types it is refused: json_schema assertions apply to URL and API monitors only.

Operator: none. The value is the schema itself, as JSON text.

In the dashboard#

1. In assertions, select + add assertion and choose json_schema.
2. The operator and value boxes change to the text the JSON body must match this schema and a large text box.
3. Paste your schema and save.

• If the text is not JSON, the form shows Not valid JSON: with the reason.
• The hint under the box reads: A $ref must point inside the schema. The schema is checked when you save.
• On the monitor page, the assertion reads json_schema body matches schema. Select it to see the schema.

{
  "type": "object",
  "required": ["id", "items"],
  "properties": {
    "id": {"type": "integer"},
    "items": {
      "type": "array",
      "items": {
        "type": "object",
        "required": ["sku", "price"],
        "properties": {
          "sku": {"type": "string"},
          "price": {"type": "number"}
        }
      }
    }
  }
}

What you can use#

• JSON Schema has versions, called drafts. obsrvly supports drafts 4, 6, 7, 2019-09 and 2020-12. Name your draft in $schema. Without it, obsrvly uses 2020-12.
• format (for example, a date or an email address) is checked in draft 7 and earlier only.
• $ref lets one part of a schema reuse another part. It must point inside the same schema, such as #/$defs/item. obsrvly does not fetch other files.
• pattern uses the same regular expressions as matches (4.1).
• Whole numbers larger than 2^53 are not compared exactly.

Limits#

obsrvly checks the schema when you save. If it cannot use it, saving fails with the reason. Examples: schema is not valid JSON, schema must be a JSON object, schema has more than 2000 objects, or schema refers to "...", which is outside the document; only references inside the schema are allowed.

When it fails: the message lists up to three problems, each with its place in the response. More problems end with ; and N more. For example, assertion json_schema: $.items[0].price: expected number, got string means the first item's price is text, not a number.