What is Jsonnet?

Jsonnet is a small programming language designed to make writing JSON data easier and more reusable. It lets you use variables, functions, and imports so you can generate complex JSON files without copying and pasting.

Let's break it down

  • small programming language: a simple set of rules you can write code in, not a huge, complicated language.
  • designed to make writing JSON data easier: its main job is to help you create JSON (the text format many apps use) with less effort.
  • variables, functions, and imports: tools that let you store values, reuse pieces of code, and bring in other files, just like in other programming languages.
  • generate complex JSON files: automatically produce big or intricate JSON structures that would be hard to type by hand.
  • without copying and pasting: you avoid repeating the same text over and over, which reduces mistakes.

Why does it matter?

Because JSON is everywhere-from configuration files to API responses-being able to create it programmatically saves time, reduces errors, and makes it simple to keep many related files consistent.

Where is it used?

  • Configuring large cloud services (e.g., Kubernetes manifests) where many similar files are needed.
  • Defining infrastructure-as-code templates for tools like Terraform or Pulumi.
  • Generating test data or mock responses for software testing.
  • Building UI component libraries where component props are stored as JSON.

Good things about it

  • Concise syntax: less typing than raw JSON.
  • Reusability: variables and functions let you share logic across files.
  • Strong typing: catches mistakes early before the JSON is produced.
  • Easy to integrate: works with existing JSON tools and pipelines.
  • Human-readable output: the generated JSON is clean and formatted.

Not-so-good things

  • Learning curve: beginners need to grasp basic programming concepts first.
  • Limited ecosystem: fewer libraries and IDE plugins compared to mainstream languages.
  • Debugging can be tricky: errors may point to generated JSON rather than the source Jsonnet code.
  • Not ideal for tiny, one-off JSON files where the overhead isn’t worth it.