CUE (Configure, Unify, Execute) is another well-regarded schema language, useful for defining valid fields, types, and values for a config.CUE was developed at Google by Marcel van Lohuizen, one of the original creators of Go. The original motivation stemmed from Google’s internal struggles in managing complex, large-scale configurations for infrastructure and applications. JSON and YAML were too weak for expressing constraints, logic, or composition, so CUE set out to solve that.Instead of building and managing external tools to validate, patch, or generate configs, CUE itself is a fully programmable config engine. This means CUE wholly encapsulates the configuration data, the schema, and the logic (how to derive those config values).
@miru(config_type="communication")control_loop_rate_hz: number & >=1 & <=1000 | *50watchdog_timeout_ms: number & >=100 & <=5000 | *500network: { max_latency_ms: number & >=10 & <=1000 | *100 connection_timeout_ms: number & >=100 & <=10000 | *2000 reconnect_attempts: number & >=1 & <=10 | *3 reconnect_interval_ms: number & >=100 & <=5000 | *1000 heartbeat_interval_ms: number & >=50 & <=1000 | *250}logging: { enable_packet_logging: bool | *true log_level: "debug" | "info" | "warn" | "error" | *"info" max_log_size_mb: number & >=1 & <=1024 | *100 retain_logs_days: number & >=1 & <=90 | *30}error_handling: { max_consecutive_failures: number & >=1 & <=20 | *5 failure_timeout_ms: number & >=100 & <=30000 | *5000 enable_auto_recovery: bool | *true}
Although many of CUE’s capabilities are omitted in this example, you’ll find some of the most commonly used features, including:
type specification - number, string, bool, etc.
numeric constraints- >=, <=, ==, !=, =~, !~, etc.
default values - | *value
enumerations - | "value1" | "value2" | "value3"
intersection of constraints - &
As you can see, CUE inlines constraints directly with type definitions, making schemas significantly more concise than JSON Schema. For more information on the supported features of CUE, check out the CUE tour on the official CUE website.
