Standard Library

Pkl's standard library is the set of pkl: modules and built-in types that make the language useful beyond raw object literals. This page is a reading map, not a replacement for exhaustive signatures in the official package docs.

Reading Map

Area	Start With	Use For
Core types	`pkl:base`	strings, numbers, booleans, collections, conversions
Math	`pkl:math`	numeric helpers and constants
Reflection	`pkl:reflect`	inspecting modules, classes, and values
Formats	`pkl:json`, `pkl:yaml`, `pkl:xml`	format-specific helpers and render behavior
Testing	`pkl:test`	assertions, examples, and package checks
Versions	`pkl:semver`	version parsing and compatibility rules

Base Module

pkl:base is where primitive values and common collection behavior become practical. When a method feels like it should exist on String, Int, Listing, or Mapping, look in the base module before writing a helper.

pkl

name = "api"labels = new Listing {  "public"  "stable"}

Keep examples conservative when teaching the language model. Reach for standard library methods after the object shape is already clear.

Format Modules

Format modules matter when output has to line up with another system. Use Output Formats for renderer behavior, then consult the relevant pkl: module when values need format-specific construction or escaping.

Testing Module

Use pkl:test to turn package expectations into executable documentation.

bash

pkl test tests/*.pkl

Tests are especially useful for templates because they show which amendments are supported and which constraints are intentionally enforced.

Reflection

Reflection is for tools and package authors. Use it when generating documentation, checking package contracts, or writing helpers that need to inspect declarations rather than only evaluate values.

Versioning

pkl:semver belongs near package boundaries. Use semantic version logic when a package must compare dependency ranges, release channels, or generated artifact versions.

Documentation Rule

For this unofficial site:

teach the language concept in Learn pages
summarize the module family here
link to package documentation when exhaustive function signatures matter
keep runnable examples small enough to evaluate