The CUE Data Constraint Language
Configure, Unify, Execute
CUE is an open source data constraint language which aims to simplify tasks involving defining and using data.
It is a superset of JSON, allowing users familiar with JSON to get started quickly.
What is it for?
You can use CUE to
- define a detailed validation schema for your data (manually or automatically from data)
- reduce boilerplate in your data (manually or automatically from schema)
- extract a schema from code
- generate type definitions and validation code
- merge JSON in a principled way
- define and run declarative scripts
CUE merges the notion of schema and data. The same CUE definition can simultaneously be used for validating data and act as a template to reduce boilerplate. Schema definition is enriched with fine-grained value definitions and default values. At the same time, data can be simplified by removing values implied by such detailed definitions. The merging of these two concepts enables many tasks to be handled in a principled way.
Constraints provide a simple and well-defined, yet powerful, alternative to inheritance, a common source of complexity with configuration languages.
The CUE scripting layer defines declarative scripting, expressed in CUE, on top of data. This solves three problems: working around the closedness of CUE definitions (we say CUE is hermetic), providing an easy way to share common scripts and workflows for using data, and giving CUE the knowledge of how data is used to optimize validation.
There are many tools that interpret data or use a specialized language for a specific domain (Kustomize, Ksonnet). This solves dealing with data on one level, but the problem it solves may repeat itself at a higher level when integrating other systems in a workflow. CUE scripting is generic and allows users to define any workflow.
CUE is designed for automation. Some aspects of this are:
- convert existing YAML and JSON
- automatically simplify configurations
- rich APIs designed for automated tooling
- arbitrary-precision arithmetic
- generate CUE templates from source code
- generate source code from CUE definitions (TODO)
Download and Install
Install using Homebrew
Using Homebrew, you can install using the CUE Homebrew tap:
brew install cuelang/tap/cue
Install From Source
If you already have Go installed, the short version is:
go get -u cuelang.org/go/cmd/cue
This will install the
cue command line tool.
For more details see Installing CUE.
The fastest way to learn the basics is to follow the tutorial on basic language constructs.
A more elaborate tutorial demonstrating of how to convert and restructure an existing set of Kubernetes configurations is available in written form.
Language Specification: official CUE Language specification.
API: the API on godoc.org
Builtin packages: builtins available from CUE programs
cueCommand line reference: the
Our canonical Git repository is located at https://cue.googlesource.com.
To contribute, please read the Contribution Guide.
To report issues or make a feature request, use the issue tracker.
Changes can be contributed using Gerrit or Github pull requests.
You can get in touch with the cuelang community in the following ways:
- Chat with us on our Slack workspace.
Unless otherwise noted, the CUE source files are distributed under the Apache 2.0 license found in the LICENSE file.
This is not an officially supported Google product.
There is no documentation for this package.
|cue||Package cue creates, evaluates and manipulates CUE configurations.|
|cue/ast||Package ast declares the types used to represent syntax trees for CUE packages.|
|cue/build||Package build defines data types and utilities for defining CUE configuration instances.|
|cue/encoding||Package encoding provides support for managing data format files supported by CUE.|
|cue/errors||Package errors defines shared types for handling CUE errors.|
|cue/format||Package format implements standard formatting of CUE configurations.|
|cue/literal||Package literal implements conversions to and from string representations of basic data types.|
|cue/load||Package load loads CUE instances.|
|cue/parser||Package parser implements a parser for CUE source files.|
|cue/scanner||Package scanner implements a scanner for CUE source text.|
|cue/token||Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates).|
|cuego||Package cuego allows using CUE constraints in Go programs.|
|encoding||Package encoding contains subpackages to convert CUE to and from byte-level and textual representations.|
|encoding/gocode||Package gocode defines functions for extracting CUE definitions from Go code and generating Go code from CUE values.|
|encoding/gocode/gocodec||Package codec converts Go to and from CUE and validates Go values based on CUE constraints.|
|encoding/json||Package json converts JSON to and from CUE.|
|encoding/jsonschema||Package jsonschema converts JSON Schema to CUE JSON Schema data is presented in CUE, so any of the supported encodings that can represent JSON Schema data can be used as a source.|
|encoding/openapi||Package openapi provides functionality for mapping CUE to and from OpenAPI v3.0.0.|
|encoding/protobuf||Package protobuf defines functionality for parsing protocol buffer definitions and instances.|
|encoding/yaml||Package yaml converts YAML encodings to and from CUE.|
|internal||Package internal exposes some cue internals to other packages.|
|internal/cmd/qgo||qgo builds CUE builtin packages from Go packages.|
|internal/copy||Package copy provides utilities to copy files and directories.|
|internal/source||Package source contains utility functions that standardize reading source bytes across cue packages.|
|internal/str||Package str provides string manipulation utilities.|
|internal/task||Package task provides a registry for tasks to be used by commands.|
|internal/third_party/yaml||Package yaml implements YAML support for the Go language.|
|internal/walk||Package walk allows walking over CUE values.|
|pkg||Package pkg define CUE standard packages.|
|pkg/encoding/base64||Package base64 implements base64 encoding as specified by RFC 4648.|
|pkg/list||Package list contains functions for manipulating and examining lists.|
|pkg/net||Package net provides net-related type definitions.|
|pkg/strings||Package strings implements simple functions to manipulate UTF-8 encoded strings.package strings.|
|pkg/struct||Package struct defines utilities for struct types.|
|pkg/time||Package time defines time-related types.|
|pkg/tool||Package tool defines statefull operation types for cue commands.|
|pkg/tool/cli||Package cli provides tasks dealing with a console.|
|pkg/tool/exec||Package exec defines tasks for running commands.|
|pkg/tool/file||Package file provides file operations for cue tasks.|
|pkg/tool/http||Package http provides tasks related to the HTTP protocol.|
|pkg/tool/os||Package os defines tasks for retrieving os-related information.|
|tools/fix||Package fix contains functionality for writing CUE files with legacy syntax to newer ones.|
|tools/trim||Package trim removes definitions that may be inferred from templates.|