1<!--
2 Copyright 2018 The CUE Authors
3
4 Licensed under the Apache License, Version 2.0 (the "License");
5 you may not use this file except in compliance with the License.
6 You may obtain a copy of the License at
7
8 http://www.apache.org/licenses/LICENSE-2.0
9
10 Unless required by applicable law or agreed to in writing, software
11 distributed under the License is distributed on an "AS IS" BASIS,
12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 See the License for the specific language governing permissions and
14 limitations under the License.
15-->
16[](https://pkg.go.dev/cuelang.org/go)
17[](https://github.com/cue-lang/cue/actions/workflows/trybot.yml?query=branch%3Amaster+event%3Apush)
18[](https://golang.org/dl/)
19[]()
20[](https://hub.docker.com/r/cuelang/cue)
21
22# The CUE Data Constraint Language
23
24_Configure, Unify, Execute_
25
26CUE is an open source data constraint language which aims
27to simplify tasks involving defining and using data.
28
29It is a superset of JSON,
30allowing users familiar with JSON to get started quickly.
31
32
33### What is it for?
34
35You can use CUE to
36
37- define a detailed validation schema for your data (manually or automatically from data)
38- reduce boilerplate in your data (manually or automatically from schema)
39- extract a schema from code
40- generate type definitions and validation code
41- merge JSON in a principled way
42- define and run declarative scripts
43
44
45### How?
46
47CUE merges the notion of schema and data.
48The same CUE definition can simultaneously be used for validating data
49and act as a template to reduce boilerplate.
50Schema definition is enriched with fine-grained value definitions
51and default values.
52At the same time,
53data can be simplified by removing values implied by such detailed definitions.
54The merging of these two concepts enables
55many tasks to be handled in a principled way.
56
57Constraints provide a simple and well-defined, yet powerful, alternative
58to inheritance,
59a common source of complexity with configuration languages.
60
61
62### CUE Scripting
63
64The CUE scripting layer defines declarative scripting, expressed in CUE,
65on top of data.
66This solves three problems:
67working around the closedness of CUE definitions (we say CUE is hermetic),
68providing an easy way to share common scripts and workflows for using data,
69and giving CUE the knowledge of how data is used to optimize validation.
70
71There are many tools that interpret data or use a specialized language for
72a specific domain (Kustomize, Ksonnet).
73This solves dealing with data on one level, but the problem it solves may repeat
74itself at a higher level when integrating other systems in a workflow.
75CUE scripting is generic and allows users to define any workflow.
76
77
78### Tooling
79
80CUE is designed for automation.
81Some aspects of this are:
82
83- convert existing YAML and JSON
84- automatically simplify configurations
85- rich APIs designed for automated tooling
86- formatter
87- arbitrary-precision arithmetic
88- generate CUE templates from source code
89- generate source code from CUE definitions (TODO)
90
91
92### Download and Install
93
94#### Release builds
95
96[Download](https://github.com/cue-lang/cue/releases) the latest release from GitHub.
97
98#### Run with Docker
99
100The release binaries are published as a Docker image described by our [Dockerfile](Dockerfile):
101
102 docker run cuelang/cue version
103
104#### Install using Homebrew
105
106Using [Homebrew](https://brew.sh), you can install using the CUE Homebrew tap:
107
108 brew install cue-lang/tap/cue
109
110#### Install from Source
111
112You need Go 1.21 or later to build CUE from source; follow the instructions at https://go.dev/doc/install.
113
114To download and install the `cue` command line tool, run:
115
116 go install cuelang.org/go/cmd/cue@latest
117
118### Learning CUE
119
120The fastest way to learn the basics is to follow the
121[tutorial on basic language constructs](./doc/tutorial/basics/Readme.md).
122
123A more elaborate tutorial demonstrating how to convert and restructure
124an existing set of Kubernetes configurations is available in
125[written form](./doc/tutorial/kubernetes/README.md).
126
127### References
128
129- [Language Specification](./doc/ref/spec.md): official CUE Language specification.
130
131- [API](https://pkg.go.dev/cuelang.org/go/cue): the API on pkg.go.dev
132
133- [Builtin packages](https://pkg.go.dev/cuelang.org/go/pkg): builtins available from CUE programs
134
135- [`cue` Command line reference](./doc/cmd/cue.md): the `cue` command
136
137### Go release support policy
138
139As a general rule, we support the two most recent major releases of Go,
140matching Go's [security policy](https://go.dev/doc/security/policy).
141For example, if CUE v0.7.0 is released when Go's latest version is 1.21.5,
142v0.7.x including any following bugfix releases will require Go 1.20 or later.
143
144### Contributing
145
146To contribute, please read the [Contribution Guide](CONTRIBUTING.md).
147
148## Code of Conduct
149
150Guidelines for participating in CUE community spaces and a reporting process for
151handling issues can be found in the [Code of
152Conduct](https://cuelang.org/docs/contribution_guidelines/conduct).
153
154## Contact
155
156You can get in touch with the cuelang community in the following ways:
157
158- Ask questions via [GitHub Discussions](https://github.com/cue-lang/cue/discussions)
159- Chat with us on our [Slack workspace](https://join.slack.com/t/cuelang/shared_invite/enQtNzQwODc3NzYzNTA0LTAxNWQwZGU2YWFiOWFiOWQ4MjVjNGQ2ZTNlMmIxODc4MDVjMDg5YmIyOTMyMjQ2MTkzMTU5ZjA1OGE0OGE1NmE).
160- Subscribe to our [Community Calendar](https://cuelang.org/s/community-calendar) for community calls, demos, office hours, etc
161
162---
163
164Unless otherwise noted, the CUE source files are distributed
165under the Apache 2.0 license found in the LICENSE file.
166
View as plain text