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0.9.2 • Public • Published

Salty Dog

salty-dog is a tool to validate JSON and YAML data using JSON schema rules. It can filter elements and validate select parts of the document, supports multiple documents in the same stream or file, and can insert defaults during validation.

Check out the getting started guide.



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salty-dog is written in Typescript and requires make, node, and yarn to build. It can be built locally or in a container.

Please see the build docs for more details.


salty-dog is distributed as a docker container and an npm package.

While the container is the preferred way of running salty-dog, it has one limitation: docker run combines stdout and stderr, making it impossible to separate logs and the output document. Writing either the logs or dest to a file works around this.

Using The Container

To run the Docker container: docker run --rm ssube/salty-dog:master

The latest semi-stable image is published to ssube/salty-dog:master. Containers are published based on both Alpine Linux and Debian (currently Stretch). All of the available tags are listed here.

Rules are provided in the image at /salty-dog/rules. To use custom rules in the container, mount them with -v $(pwd)/rules:/salty-dog/rules:ro and load them with --rules /rules/foo.yml.

The ssube/salty-dog container image can be run normally or interactively.

To validate a file or input normally:

> docker run --rm ssube/salty-dog:master --help

You can also launch a shell within the container, using local rules:

> docker run \
    --rm \
    -it \
    --entrypoint bash \

Using The Package

salty-dog is also published as an npm package with a binary, so it can be used as a CLI command or programmatically.

Project Package

To install salty-dog for the current project:

> yarn add -D salty-dog
> $(yarn bin)/salty-dog --help

Global Package

It is also possible to install salty-dog globally, rather than within a project. However, this is not recommended.

> yarn global add salty-dog
> export PATH="${PATH}:$(yarn global bin)"
> salty-dog --help

Usage Modes

salty-dog can run in a few different modes: check mode will report errors, fix mode will attempt to modify the input document, and list mode will print the active set of rules.

Check Mode

By default, salty-dog will validate the structure and contents of the --source document. If all rules pass, the document will be printed to --dest.

> cat examples/kubernetes-resources-pass.yml | salty-dog \
    --rules rules/kubernetes.yml \
    --tag kubernetes

[2019-06-15T23:53:34.223Z]  INFO: salty-dog/19839 on cerberus: all rules passed

> cat examples/kubernetes-resources-fail.yml | salty-dog \
    --rules rules/kubernetes.yml \
    --tag kubernetes

[2019-06-15T23:56:04.764Z] ERROR: salty-dog/22211 on cerberus: some rules failed (errors=1)

The --source and --dest default to stdin and stdout, respectively, but a path may be provided:

> salty-dog \
    --rules rules/kubernetes.yml \
    --tag kubernetes \
    --source examples/kubernetes-resources-pass.yml \
    --dest /tmp/kubernetes-resource.yml

[2019-06-15T23:53:34.223Z]  INFO: salty-dog/19839 on cerberus: all rules passed

Fix Mode

salty-dog can also add default values to missing properties in fix mode. If a rule does not immediately pass with the --source document, but defaults are provided in the schema, the defaults will be inserted before printing to --dest.

> salty-dog fix \
    --source examples/kubernetes-resources-some.yml \
    --rules rules/kubernetes.yml \
    --tag kubernetes
Default Values

Properties that appear in the schema with a default provided will be added to each element as it is checked. Rules apply in order, as do their defaults.

Coercing Values

Properties that appear in the document with a different type than they have in the schema may be coerced, if the value is compatible with the schema type. The full matrix of valid type coercions is documented by Ajv.

List Mode

salty-dog can list the active set of rules, to help debug tags and inclusion. Both --source and --dest are ignored in list mode.

> salty-dog list \
    --rules rules/kubernetes.yml \
    --tag kubernetes

[2019-06-30T18:39:11.930Z]  INFO: salty-dog/26330 on cerberus: listing active rules
    rules: [
        "desc": "resource limits are too low",
        "level": "debug",
        "name": "kubernetes-resources-minimum-cpu",


Formatting Logs

salty-dog uses node-bunyan for logging and prints structured JSON output. Logs can be pretty-printed by redirecting stderr through bunyan itself or jq, both of which are installed in the salty-dog container:

> cat resource.yml | salty-dog --rules rules/kubernetes.yml --tag kubernetes 2> >(bunyan)

[2019-06-15T23:53:34.223Z]  INFO: salty-dog/19839 on cerberus: all rules passed

> cat resource.yml | salty-dog --rules rules/kubernetes.yml --tag kubernetes 2> >(jq)

  "name": "salty-dog",
  "hostname": "cerberus",
  "pid": 19839,
  "level": 30,
  "msg": "all rules passed",
  "time": "2019-06-15T23:53:34.223Z",
  "v": 0

Using jq allows for additional filtering and formatting. For example, jq 'select(.level > 30)' will only print warnings and errors (the minimum log level to print can be set in the configuration file).

To print the last line's message and error messages: tail -1 | jq '[.msg, try (.errors[] | .msg)]'

> cat test/examples/kubernetes-resources-high.yml | salty-dog \
    --rules rules/kubernetes.yml \
    --tag kubernetes 2> >(tail -1 | jq '[.msg, try (.errors[] | .msg)]')

  "all rules passed"

> cat test/examples/kubernetes-resources-some.yml | salty-dog \
    --rules rules/kubernetes.yml \
    --tag kubernetes 2> >(tail -1 | jq '[.msg, try (.errors[] | .msg)]')

  "some rules failed",
  ".resources.limits should have required property 'memory' at $.spec.template.spec.containers[*] for kubernetes-resources",
  ".metadata should have required property 'labels' at $ for kubernetes-labels"


Rules combine a jsonpath expression and JSON schema to select and validate the document.

The rule's select expression is used to select nodes that should be validated, which are filtered, then checked.

The structure of rule files and the rules within them are documented here.

Loading Rule Sources

Rules can be loaded from a file, module, or path.

To load a file by name, --rule-file foo.yml. This will accept any extension.

To load a module, --rule-module foo. The required module exports are documented here.

To load a path, --rule-path foo/. This will recursively load any files matching *.+(json|yaml|yml).

Using Rule Tags

All rules are disabled by default and must be enabled by name, level, or tag.

To enable a single rule by name, --include-name foo-rule.

To enable a group of rules by level, --include-level warn.

To enable a group of rules by tag, --include-tag foo.

Validating Rules

To validate the rules in the rules/ directory using the meta-rules:

> make test-rules

{"name":"salty-dog","hostname":"cerberus","pid":29403,"level":30,"msg":"all rules passed","time":"2019-06-16T00:56:55.132Z","v":0}


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