JSON Schema is probably the most popular schema language. With origins dating back to 2010, JSON Schema was initially built for API validation. Since then, it has found its way into configuration systems across web, cloud, and robotics infrastructure.
Below is an example JSON Schema to give you a flavor of what JSON Schema looks like:
JSON Schema
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$schema: "https://json-schema.org/draft/2020-12/schema"title: Communication Configuration Schematype: objectrequired: - control_loop_rate_hz - watchdog_timeout_ms - network - logging - error_handlingproperties: control_loop_rate_hz: type: integer description: Control loop frequency in Hertz minimum: 1 maximum: 1000 default: 50 watchdog_timeout_ms: type: integer description: Watchdog timeout duration in milliseconds minimum: 100 maximum: 5000 default: 500 network: type: object required: - max_latency_ms - connection_timeout_ms - reconnect_attempts - reconnect_interval_ms - heartbeat_interval_ms properties: max_latency_ms: type: integer description: Maximum acceptable network latency in milliseconds minimum: 10 maximum: 1000 default: 100 connection_timeout_ms: type: integer description: Connection timeout duration in milliseconds minimum: 100 maximum: 10000 default: 2000 reconnect_attempts: type: integer description: Number of reconnection attempts minimum: 1 maximum: 10 default: 3 reconnect_interval_ms: type: integer description: Interval between reconnection attempts in milliseconds minimum: 100 maximum: 5000 default: 1000 heartbeat_interval_ms: type: integer description: Interval between heartbeat messages in milliseconds minimum: 50 maximum: 1000 default: 250 logging: type: object required: - enable_packet_logging - log_level - max_log_size_mb - retain_logs_days properties: enable_packet_logging: type: boolean description: Enable or disable packet logging default: true log_level: type: string description: Logging level enum: ["debug", "info", "warn", "error"] default: "info" max_log_size_mb: type: integer description: Maximum log file size in megabytes minimum: 1 maximum: 1024 default: 100 retain_logs_days: type: integer description: Number of days to retain log files minimum: 1 maximum: 90 default: 30 error_handling: type: object required: - max_consecutive_failures - failure_timeout_ms - enable_auto_recovery properties: max_consecutive_failures: type: integer description: Maximum number of consecutive failures allowed minimum: 1 maximum: 20 default: 5 failure_timeout_ms: type: integer description: Timeout duration for failure handling in milliseconds minimum: 100 maximum: 30000 default: 5000 enable_auto_recovery: type: boolean description: Enable or disable automatic recovery from failures default: true
Although many of JSON Schema’s capabilities are omitted in this example, you’ll find some of the most common keywords, including:
$schema - the JSON Schema draft version
type - the data type of a property
required - the property must exist
properties - the sub-fields of an object
default - the default value of a property
description - a human-readable description of a property
enum - a constrained list of values a property can take
minimum - the minimum value of a property
maximum - the maximum value of a property
For a comprehensive list of JSON Schema keywords, visit the official JSON Schema website. We also find the official test suite highly useful, as it contains a large number of simple JSON Schema examples.
While JSON Schema has multiple drafts, only Draft 2020-12, the most recent stable draft, is supported.When specifying the $schema keyword in a schema, it must be set to the following value:
While JSON Schema was originally built for JSON data, it is not exclusive to JSON. JSON Schema may be uploaded to Miru in the following formats:
JSON (.json)
YAML (.yaml, .yml)
The format of a schema does not need to match the format of the config instance it validates. For example, a YAML-formatted JSON Schema can validate a JSON-formatted config instance.JSON Schemas can validate config instances in the following formats:
