jsonnet

data templating language that generates JSON

TLDR

Evaluate Jsonnet file

$ jsonnet [file.jsonnet]

Output to file

$ jsonnet [file.jsonnet] -o [output.json]

Evaluate with external variable

$ jsonnet --ext-str [name=value] [file.jsonnet]

Multi-file output

$ jsonnet -m [output_dir] [file.jsonnet]

Evaluate expression

$ jsonnet -e "[{a: 1, b: 2}]"

Format Jsonnet file

$ jsonnetfmt [file.jsonnet]

Jsonnet is a data templating language that generates JSON. It adds variables, conditionals, functions, and imports to JSON, making configuration files more maintainable.Jsonnet is used for generating Kubernetes manifests, Prometheus configurations, and other JSON/YAML configs. It evaluates to pure JSON.

PARAMETERS

-o file

Output file.

-m dir

Multi-file output directory.

-e code

Evaluate expression.

--ext-str name=value

External string variable.

--ext-code name=code

External code variable.

-J dir

Add library search path.

-S, --string

Output as string.

--tla-str name=value

Top-level argument string.

EXAMPLE

$ local person(name, age) = {
  name: name,
  age: age,
};

{
  people: [
    person("Alice", 30),
    person("Bob", 25),
  ]
}

INSTALL

sudo apt install jsonnet

sudo dnf install jsonnet

sudo apk add jsonnet

brew install jsonnet

nix profile install nixpkgs#jsonnet

CAVEATS

Output is always JSON (use for YAML via conversion). No side effects; pure functional. Libraries need -J path. Not for runtime config.

HISTORY

Jsonnet was developed at Google by Dave Cunningham around 2014. It addressed the need for DRY configuration in cloud infrastructure, gaining adoption in the Kubernetes ecosystem.